Brief Review
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The Acute Effects From the Use of Weighted
Implements on Skill Enhancement in Sport: A
Systematic Review
Sam Jermyn, Cian O’Neill, and Edward K. Coughlan
Department of Sport, Leisure & Childhood Studies, Munster Technological University, Cork Campus, Cork, Ireland
Abstract
Jermyn, S, Neill, CO, and Coughlan, EK. The acute effects from the use of weighted implements on skill enhancement in sport: A
systematic review. J Strength Cond Res 35(10): 2922–2935, 2021—Weighted implements are used before competitive performance with the aim of enhancing motor skill execution on return to the standard implement. The purpose of this review was to
analyze the existing literature pertaining to the acute effects of weighted implements on respective sporting performance. Following
a systematic screening process, 25 studies were identified. This review highlighted the effects of (a) weighted balls and bats on
throwing and batting performance and (b) indoor weight throw implements on indoor weight throw performance. Studies reported
conflicting effects on immediate performance post–warm-up with the respective implements. Notably, although overweighted bats
and overweight attachments are a prominent preparatory tool in baseball, this review found consistent and repeated evidence of
degraded batting performance in striking-based studies. Decreased bat velocity, altered swing patterns, subjective-objective
mismatches of bat speed and weight, temporal accuracy errors, and inadequate recalibration to the standard bat were identified as
acute effects. This review identified an obvious dearth of research into the acute effects of weighted implements on motor skills in
other sports with equally complex perceptual motor patterns, such as football (soccer), golf, rugby, basketball, and American
football. Future weighted implement research should investigate the acute effects of respective implements on motor skill performance in other sports, such as those aforementioned, with the purpose of exploring relevant implications for preparatory
strategies and immediate performance on return to the standard implement.
Key Words: weighted implement training, warm-up, overload, underload, skill acquisition
Introduction
The development and improvement of motor skills is an integral
factor in the attainment of sporting success (16,38). Consequently, athletes, coaches, and researchers are on a constant quest
to explore and identify the most effective means of enhancing
sport-specific motor skills. In particular, because of recent research and programming trends placing greater emphasis on
specificity and efficient training modalities, a substantial volume
of empirical research has been conducted on the acute and chronic
effects of weighted implements over the past 3 decades (4).
Weighted implement training involves exercising with modified
sporting implements while duplicating the force-velocity output
and full range of motion of the respective motor skill (6,7). This
includes swinging a baseball bat that is heavier or lighter than
regulation weight or throwing an overweighted or underweighted
baseball to prime the accelerative properties of a desired action in
preparation to compete. As weighted implement training maintains high specificity between the weighted movement and the
original movement (9), it has been categorized as a form of specific resistance training, in which the principle of speed overload
(underweighted implements) or force overload (overweighted
implements) can be applied (10,46).
Research assessing the efficacy of weighted implement training
as a means of performance enhancement dates back to the early
Address correspondence to Sam Jermyn, sam.jermyn@mycit.ie.
Journal of Strength and Conditioning Research 35(10)/2922–2935
ª 2021 National Strength and Conditioning Association
1960s (50). The aim of this seminal research, as well as the subsequent research to date, has been to investigate the potential of
weighted implement training to enhance key variables underlying
the successful outcome of sport-specific motor skills, with a
prevalence for assessing their effects on pitching and batting velocity (4,9,12,43,46,47). Some studies have also assessed the effects of a weighted football on kick distance (1) and a weighted
cricket ball on speed of bowling (51). However, these studies
collectively report inconsistencies pertaining to the effectiveness
of chronic weighted implement training programs at enhancing
motor skills. Therefore, although various studies since the turn of
the 21st century have investigated the training effects of weighted
implements (4), the aforementioned inconsistencies pertaining to
the effectiveness of weighted implement training programs have
resulted in a considerable portion of weighted implement training
research investigating its acute effects (26). These studies that
have investigated the acute effects of weighted implement training
have, therefore, investigated the efficacy of using weighted implements as a warm-up strategy. A prominent purpose of these
studies has been to investigate the acute effects of underweighted
and overweighted balls and bats on baseball pitching and batting
velocity. Studies have investigated the acute effects of multiple
readily available implements of varying mass and moments of
inertia on baseball pitching and batting, with pitching accuracy
and pitching and batting velocity, being the most commonly
assessed performance variables. In many throwing and pitching
sports, enhancing throwing velocity and accuracy is considered
integral to competitive success. For example, the development of
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speed and accuracy among baseball players may result in less time
for opponents to react to an on-target pitch, therefore enhancing
the pitcher’s potential to strike out the batter (4). Similarly, increasing cricket or softball outfield players’ ability to throw at
higher speeds with greater accuracy may increase the likelihood of
completed passes to teammates and enhance the chances of
eliminating an opponent. With regard to batting performance,
enhancement of bat velocity is considered integral to performance
as increased velocity values result in a faster swing time. This
provides batters with greater time to obtain information from ball
flight due to the affordance of delaying swing onset times, subsequently producing greater batted-ball distances and velocities (46).
Several research studies have compared motor skill performance with regulation and weighted implements (14,22,49,51).
Although these studies have not included follow-up measures of
performance on return to the regulation implement, their findings provide an insight into the potential implications of using
the respective implement immediately before competitive performance. Consequently, athletic performance stakeholders,
such as strength and conditioning (S&C) coaches and skill acquisition specialists, are provided with substantial evidence
pertaining to the acute effects of weighted implements. Such
studies have also made varying suggestions as to the optimal
programming of weighted implement training to induce immediate enhancements of motor skill performance. Therefore,
S&C coaches and skill acquisition specialists are provided with
an abundance of findings, and corresponding suggestions pertaining to their programming, which need to be synthesized.
Because of the importance of sport-specific motor skill proficiency in sporting success (25), identifying and using effective
preparatory tools and routines is a priority for practitioners and
athletes, leading to this comprehensive analysis of the existing
literature. To date, the weighted implement training literature
has been of greater interest to baseball; however, there is also a
need to identify sports that require investigation into the acute
effects of weighted implement training on respective motor skill
performance. Therefore, the purpose of this systematic review is
2-fold: (a) to assess the acute effects of weighted implement
training on sports performance, providing a comprehensive
overview of the research to-date, and (b) to provide recommendations to guide future research in the weighted implement
training field.
Methods
Experimental Approach to the Problem
A systematic review was conducted in accordance with the
PRISMA (Preferred Recording Items for Systematic MetaAnalyses) guidelines (28). Terms including “weighted implement,” “modified implement,” “weighted football,” “heavy
bat,” “weighted club,” “weighted racquet,” and “weighted
baseballs” were searched across 6 databases including Google
Scholar, EBSCOhost, MEDLINE, SPORTDiscus, Science Direct, and Academic Search Complete. The search focused on
the literature from inception to November 2019 to allow for
the potential inclusion of all relevant studies.
Procedures
Following the online systematic screen outlined in Figure 1, duplicate studies were removed with a subsequent screen of the
remaining studies’ abstracts. The full-text articles were retrieved,
and a comprehensive review was conducted to ensure that all
inclusion criteria were adhered to. Additional analyses of reference lists of included articles were conducted, with direct contact
established with authors of identified studies that were not accessible online. From each identified study, the following experimental features were extracted and analyzed: the subject
population, standard implement weight, weight deviation of the
modified implement from standard weight, and subsequent effect
on all performance variables with standard implements. The inclusion criteria for this review were set a priori, requiring studies
to (a) include an investigation into the acute effects of a sportspecific weighted implement on immediate sport-specific motor
skill performance with the regulation implement, (b) be published
in a peer-reviewed journal or relevant conference proceedings, (c)
include a weighted implement warm-up protocol and immediate
post-test, (d) have an adult or youth subject cohort, and (e) be
written in English. Studies were excluded if only a comparative
analysis of motor skill performance between the weighted implement and regulation implement was performed, and also if the
conditioning activity used conventional resistance training
equipment including barbells, dumbbells, manual and air resistance machines, cable machines, medicine balls, and kettlebells.
Results
A total of 1,653 articles were retrieved on initial searches, of
which 116 were selected for further review. Following the removal of duplicates, 75 studies remained, of which 48 were excluded following the screening of abstracts. This resulted in a total
of 27 studies. The full texts of these articles were reviewed. Six of
these articles were subsequently excluded for reasons that included a case study design (n 5 2), an uneven sample of experimental trials per weighted implement condition due to invalid
data (n 5 1), not stating the weight of the implements used (n 5
1), the inclusion of a non–sport-specific motor skill (n 5 1), and
absence of a post–warm-up test (n 5 1). Four additional studies
were identified on screening of the included studies’ reference
lists. Subsequently, 25 studies, meeting the inclusion criteria of
this review, were included (Figure 1). In the Discussion section of
this review, all selected studies are categorized based on the type
of respective implement used: underweighted and overweighted
balls (n 5 5), weighted indoor weight throw implements (n 5 2),
and underweighted and overweighted bats (n 5 18). Studies that
used weighted bats are categorized into further subsections.
Four weighted ball studies involved the use of under and
overweighted baseballs, with 1 study investigating the effects of
weighted cricket balls on bowling performance. Seventeen dependent variables were reported, of which throwing/pitching
velocity was most frequently investigated. The 2 studies investigating the acute effects of weighted indoor weight throw
implements involved the use of overweighted indoor weight
throw implements. Three dependent variables were reported in
each study. Of the 18 studies that used a weighted bat, 17 included the use of underweighted and overweighted baseball bats
and overload attachments, whereas 1 study investigated the use of
underweighted and overweighted softball bats and overload attachments among a softball cohort. Forty-six dependent variables
were examined across these studies, with bat velocity being the
most frequently investigated marker of batting performance. The
results of this review process highlight a clear paucity of research
investigating the acute effects of other weighted implements, such
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Figure 1. Flowchart summarizing the screening and selection process (28).
as weighted footballs, rugby balls, basketballs, golf clubs, hockey
sticks, and racquet implements. The authors acknowledge that
several included studies are relevant to multiple sections within
the discussion (for example, Weighted Ball Studies and Underlying Mechanisms).
Discussion
Table 1 illustrates the included studies that investigated the acute
effects of underweighted and overweighted balls on pitching and
bowling performance with respective regulation implements (n 5
5). The greatest decrease in ball weight from the respective study’s
regulation ball was 20% (40), with the greatest increase being
200% (42). All 5 studies investigated the effects of such implements on ball velocity, with additional variables measured including pitch/bowling accuracy, muscular activation, and
perception of throwing speed and ball weight.
Although all included studies investigated the effects of
weighted balls on throwing velocity following a weighted ball
warm-up, 4 studies also assessed the impact of such protocols on
throwing accuracy with a regulation ball. Two baseball studies
reported a significant increase in pitching velocity following a
weighted baseball throwing protocol (30,50). Only 1 study
reported a subsequent improvement in accuracy (50). However,
as accuracy improvements were not statistically significantly
different between groups, it is advised that the observed
improvements in accuracy following pitches with the weighted
baseball should be interpreted with caution.
Van Huss et al. (50) reported a significant improvement (p 5
0.01) in pitching velocity from pre–warm-up to post-test following a weighted ball warm-up among 50 collegiate freshman
baseball players (each serving as their own control). Velocity of
throws in the post–overload warm-up consistently increased until
the sixth post-trial before plateauing. Pitching velocity was
measured with a chronoscope (product manufacturer details not
specified). Although accuracy diminished in the first 7 trials
post–weighted ball warm-up in comparison to the standard ball,
accuracy of the final 3 post-test trials was greater than that of the
standard warm-up. Accuracy was measured based on the ball’s
contact with a target in which various rectangular segments were
arranged. A 1–5 scoring system based on the point of contact
determined pitching accuracy.
Later in the decade, Straub (42) investigated the acute effects of
a standard baseball and 2 overweighted baseballs on the velocity
and accuracy of the overarm throw. Based on an initial velocity
assessment, 60 high school subjects were equally divided into
“high-velocity” (n 5 30) and “low-velocity” (n 5 30) groups,
with each group comprising of 3 subgroups of 10 subjects. Results
demonstrated that the overload warm-ups did not result in significant improvements (p . 0.05) in throwing velocity at either
velocity levels, with the regulation warm-up resulting in similar
velocities. Pitching velocity was measured with the use of a
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Table 1
Acute effects of underweighted and overweighted balls on throwing performance.*
Reference
Sport
Subjects
Implements (% increase/
decrease from standard)
#WU trials; rest period
between WU and post-WU;
post-WU intertrial rest
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OB significantly ↑ V
OB did not significantly ↑ A but
gradually ↑ A
No significantly ↑ V
No significantly change to A
6 or 18; minimal; N/A
Significantly ↑ V following 6 and
18 throws with UB and 18
combined throws
No significant changes in A
“Lightness” and “ease of pitching”
after OB warm-up
“Heaviness” and “difficult to pitch”
after UB warm-up
No significant differences in ball V
following each warm-up protocol
but each ball caused varying
muscular activation
No significant difference in V
OB condition significantly ↓ A vs.
RB
R 142 g (5 oz) OB 312 g (11 oz,
120% ↑)
Straub (42)
Baseball 60 male high school
students
Morimoto, Ito, Kawamura, and
Muraki (30)
Baseball 8 male university
baseball players
R 142 g (5 oz)
OB 284 g (10 oz, 100% ↑)
OB 425 g (15 oz, 200% ↑)
R 142 g (5 oz)
UB 128 g (4.5 oz, 10% ↓)
OB 156 g (5.5 oz, 10% ↑)
Shin and Choi (40)
Baseball 12 high school and
university pitchers
R 142 g (5 oz)
UB 113 g (4 oz. 20% ↓)
OB 227 g (8 oz, 60% ↑)
Feros, Young, and O’Brien (13)
Cricket
R 156 g (5.5 oz)
18; 3 min; post-test 5 4 overs
OB 300 g (10.6 oz, 92.31% ↑) and (4 3 6 throws)–3 min between
OB 250 g (8.8 oz, 60.26% ↑)
overs, 30 s between trials
17 male community-level
pace bowlers
Results and conclusions
25 (15 submaximal and 10
maximal effort throws); minimal;
N/A
20; N/A; N/A
Van Huss, Albrecht, Nelson, and Baseball 50 university freshman
Hagerman (50)
baseball players
10; 10 min; N/A
*V 5 velocity; A 5 accuracy; R 5 regulation ball; OB 5 overweight ball; UB 5 underweight ball; RB 5 regulation ball; N/A 5 not available; ↑ 5 weight increase; ↓ 5 weight decrease.
chronoscope (product manufacturer details not specified). The
overweighted implement conditions, and regulation implement
condition, did not produce any significant changes (p . 0.05) in
pitching accuracy for any group. Pitching accuracy was measured
based on the ball’s contact point with a target, in which concentric
circles on the target indicated various accuracy zones. A scoring
system was used to depict accuracy.
The aforementioned studies (42,50) exclusively used overweighted baseballs of substantially greater mass than a regulation baseball ($100% weight increase). In contrast, Morimoto
et al. (30) assessed the immediate effects of overweighted and
underweighted balls that were slightly different from the standard weight on ball speed and accuracy. Eight male university
players were required to pitch 128 g (4.5 oz), 142 g (5 oz), or 156
g (5.5 oz) baseballs. Each ball was pitched 6 or 18 times. A
combination condition, which required 6 or 18 pitches with all 3
balls (order of 156 g/5.5 oz, 142 g/5 oz, and 128 g/4.5 oz), was
also performed. Post-test velocities of the regulation baseball
were significantly faster (p , 0.01) following 6 and 18 throws
with the light ball and 18 throws under the combined condition.
However, it was reported that ball speeds following the 18
combined conditions were similar to velocity values measured
following 6 throws with the light ball, suggesting that there may
have been minimal effect from the heavy or standard ball before
pitching the light ball. Morimoto et al. (30) suggested that the
number of throws is of great importance as the 6-trial combined
condition, which concluded with 2 throws with the underweighted ball, resulted in no significant improvement (p . 0.05)
in pitch velocity. Pitching velocity was measured with a speed
gun (Mizuno, PSK-DSP; full product manufacturer details not
reported by authors). Similar to the findings of Straub (42),
accuracy scores revealed no significant difference (p . 0.05)
among all conditions. Pitching accuracy was determined based
on the ball’s contact point with a target in which an “X” was
marked in the center. Video analysis of the coordinates of this
contact point and the target center were used to determine the
displacement of each pitch (i.e., accuracy). Subjects reported
sensations of “heaviness” and “difficult to pitch” during post–
warm-up throws following the underweighted ball and feelings
of “lightness” and “ease of pitching” during post–warm-up
pitches following the overweighted ball. Thus, although slight,
the 28.35 g (1 oz) difference in weight between the underweighted and overweighted baseballs may induce altered kinesthetic perceptions of pitching performance on return to the
regulation baseball weight.
More recently, Shin and Choi (40) found no significant differences (p . 0.05) in post–warm-up pitching velocity of a regulation baseball following warm-up throws with a standard,
underweighted, or overweighted baseball. Pitching velocity was
measured with a radar gun (Sport radar, 24.7 GHZ, SP78585,
Applied Concepts, Inc., Northbrook, IL). Muscle activation of the
internal and external shoulder rotators of the pitching arm was
also measured using a wireless electromyography (EMG) device
(SENIAM Guide Line; full product manufacturer details not
reported by authors). Electromyographic activity of the biceps
brachii and triceps brachii was also assessed. Although no significant differences (p . 0.05) in pitching velocity were found,
activation of various muscles surrounding the shoulder slightly
varied dependent on warm-up condition. As shoulder internal
rotational velocity and elbow extension velocity account for 67%
of ball velocity at release (48), it was surprising that increased
activation in the muscles responsible for these variables (for example, anterior deltoid, latissimus dorsi, and triceps brachii)
following weighted ball warm-ups was not matched by significantly greater pitching velocity in post-test trials. Therefore, the
authors attributed such activation increases to compensations
from decreased pitching velocities that were exhibited when
warming up with the weighted ball. It was concluded that the
weight of the ball used in warm-ups should be selected based on
individual status, with the variation in muscular activity
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Weighted Implement Training (2021) 35:10
Table 2
Acute effects of weighted bats on batting performance with an 850 g/30 oz bat.*
Reference
Sport
Subjects
Implements (% weight
increase/decrease from
standard)
#WU trials; rest period between
WU and post-WU; post-WU
intertrial rest
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DeRenne (5)
Baseball 23 male college, ex-college, and
ex-professional players
L 5 652 g (23 oz), 709 g (25 oz), 3; immediate; minimal (rotational
765 g (27 oz)
basis within group)
H 5 S1: 794 g (28 oz) donut, “ondeck power swing,” H
DeRenne and
Branco (8)
Baseball 20 male college players
12 devices from 652 g (23 oz,
4; immediate; immediate
23.33% ↓)–1,446 g (51 oz, 70% ↑)
DeRenne et al.
(11)
Baseball 60 male high school
varsity players
13 devices from 652 g (23 oz,
23.33% ↓)–1,758 g (62 oz,
106.66% ↑)
4; minimal; 20 s
Higuchi et al. (15) Baseball 24 collegiate players
S 850 g (30 oz)
H 1,531 g (54 oz, 80% ↑)
Swing-specific isometric
contraction condition (iso)
3 (included isometric contraction
condition); 1 min; 10 s
Szymanski et al.
(45)
10 devices from 624 g (22 oz,
3; 20 s; 20 s
26.66% ↓)–2,722 g (96 oz, 220%
↑)
5 devices ranging from L 737 g (26 5; post-trials at 1, 2, 4 and mins
oz, 13.33% ↓)–H 1,417 g (50 oz, post-WU
66.66% ↑)
Baseball 22 Division 1 collegiate players
Wilson et al. (53) Baseball 16 Division II intercollegiate
players
Williams et al.
(52)
Baseball 15 varsity players
S 850 g (30 oz)
L 301 g (10.6 oz, 64.67% ↓)
H 1,576 g (55.6 oz, 85.33% ↑)
donut condition
Weighted glove condition
5; 1 min; 20 s
Results and conclusions
765 g (27 oz) bat and slightly
overweighted bat produced greatest
BV; 652 g (23 oz) bat and donut
attachment had adverse effects on
BV
709 g (25 oz) bat produced greatest
BV with donut, power sleeve, and
power swing resulting in greatest
↓BV
Approximately 610% of 850 g (30
oz) S produced greatest BV
Bats .964 g (34 oz) and ,765 g
(27 oz) produced significantly slower
BV vs 765–964 g (27–34 oz) bats;
652 g (23 oz), 1,446 g (51 oz) and
donut produced slowest BV
S did not significantly change
standard bat BV
1,531 g (54 oz) bat produced a
significant ↓ in standard bat BV; iso
acutely ↑BV
No significant difference in BV
following WU with any of the 10 bats
No significant weight effects on any
of the velocity or acceleration
variables, but pooled data revealed
PV, PA, and PVPA significantly ↑
between 4 and 8 min
No significant differences between
bats for effects on MRV, RVBC, time
between MRV and RVBC, and bat
angle at MRV and RVBC
73.3% of subjects preferred donut
condition
*L 5 light bat; H 5 heavy bat; S 5 standard bat; BV 5 bat velocity; WU 5 warm-up; MRV 5 maximal resultant velocity; RVBC 5 resultant velocity at ball contact; PVPA 5 peak bat velocity at peak
acceleration; PV 5 peak bat velocity; PA 5 peak bat acceleration; ↓ 5 decrease; ↑ 5 increase.
dependent on the weight of the ball having potential implications
for the design of long-term weighted ball training programs.
In the only cricket study included in this review, Feros et al. (13)
found no significant difference (p . 0.05) in velocity and perception of effort following standard ball and overweighted ball
warm-ups among 17 community-level bowlers. Bowling velocity
was measured with a radar gun (Stalker Pro; Applied Concepts,
TX). Although each condition did not affect bowling velocity, it
was found that the weighted warm-up condition resulted in significantly lower mean accuracy (p 5 0.049) as subjects experienced a 10.9% decrease in accuracy compared with that of the
control condition. The effect size (ES) of this difference was d 5
0.581, which indicates a medium ES (34). Bowling accuracy was
assessed by use of a vertical target sheet, which was placed in line
with the stumps at the batsman’s end of the pitch. With the use of
Dartfish Connect Version 6 (Dartfish, Australia), the distance
between ball strike and the crosshair of the target was calculated
to determine accuracy.
This review process illuminated a dearth of research into the
acute effects of underweighted and overweighted balls on
throwing and kicking performance in sports such as soccer,
rugby, Gaelic football, Australian rules football, American football, basketball, and Olympic handball. Of the existing weighted
implement training literature regarding weighted balls, the current review process highlighted multiple studies assessing the
chronic effects of weighted ball throwing programs, as only a
small proportion of the respective literature has investigated the
acute effects of this training modality on overarm throwing and
pitching. Of these studies, an overriding prevalence of investigations into the acute effects of weighted baseball implements is
apparent. Within the existing literature, there are conflicting reports of the acute effects of weighted baseballs on pitching velocity. Although it has been demonstrated that warm-ups with
127.58 g (4.5 oz) and 311.85 g (11 oz) baseballs result in significant improvements in pitching velocity, it has also been shown
that warm-ups with 113.40 g (4 oz), 155.92 g (5.5 oz), 226.80 g (8
oz), 283.50 g (10 oz), and 425.24 g (15 oz) baseballs do not lead
to significant improvements. Because of substantial differences in
methodological design, including total throws, ball weight, and
subject playing levels, comparison between studies is a complex
process. Therefore, this accentuates the need for future research to
specify optimal programming to induce immediate improvements
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Table 3
Acute effects of weighted bats on batting performance with alternative standard bats.*
Reference
Sport
Subjects
Implements (% weight
increase/decrease from
standard)
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Miller et al. (26)
Baseball
32 male recreational
players
Kim and Hinrichs
(21)
Baseball
20 male experienced players S 885 g (31.2 oz)
5; 2 minutes; 20 s
H 1,452 g (51.2 oz, 64.1% ↑) donut
condition
Arm weight condition
Montoya et al. (29) Baseball
Kim and Hinrichs
(20)
Baseball
Southard and
Groomer (41)
Baseball
Szymanski et al.
(44)
Softball
Otsuji et al. (33)
Baseball and
softball
S 822 g (29 oz)
L 181 g (6.4 oz, 77.93% ↓)
H 1,616 g (57 oz, 96.55% ↑)
#WU trials; rest period between
WU and post-WU; post-WU
intertrial rest
19 male recreational players S 893 g (31.5 oz)
L 272 g (9.6 oz, 69.52% ↓)
H 1,565 g donut condition (55.2 oz,
75.24% ↑)
13 subjects
S 909 g (32.1 oz)
L 113 g (4 oz, 87.5%↓)
H 1,477 g donut condition (52.1 oz,
62.5% ↑)
10 experienced players
S 964 g (34 oz)
H 1,588 g donut condition (56 oz,
64.71% ↑)
L 340 g (12 oz, 64.71% ↓)
19 Division 1 intercollegiate S 652 g (23 oz)
players
8 devices from 510 g to 2,722 g (18
oz, 21.74% ↓–96 oz, 317.39%↑)
8 university softball and
S 920 g (32.5 oz)
baseball players
H 1,720 g bat ring condition (60.7
oz, 86.68% ↑
3; 2–3 min; 30 s
5; 30 s; N/A
5; 2 min; N/A
5; 2 min; 15 s
3; 20 s; 20 s
5; 15 s; 15 s
Results and conclusions
S and L produced significantly
faster post-WU BV vs H
Light significantly ↑ BV pre-post and
heavy significantly ↓ BV pre-post
No significant difference in the
effects of WU bats on post-WU BV,
but a transient BV ↑ from first postWU swing to fourth post-WU swing
following S and H warm-ups
Rest period of 3-min recommended
S and L produced significantly
faster post-WU BV (vs H)
No significant differences in BV after
using any of the WU bats
Post-WU swings felt “significantly
faster” after H WU
Donut condition significantly ↓ BV
vs S and L WU’s
Weighted bats (bats of ↑MOI)
change swing patterns
No significant differences in BV after
using any of the WU bats
Donut produced lowest post–WU BV
No significant BV difference
pre–weighted and post–weighted
WU.
BV significantly ↓ during first swing
post–weighted WU, but perceived S
to be lighter and faster during this
first post–weighted swing
*L 5 light bat; H 5 heavy bat; S 5 standard bat; BV 5 bat velocity; WU 5 warm-up; ↓ 5 decrease; ↑ 5 increase; N/A 5 not available; MOI 5 moment of inertia.
in performance. However, as indicated by Morimoto et al. (30),
the amount of warm-up trials with a weighted implement seems to
have an effect on the magnitude of pitching velocity improvement,
a variable that should be further investigated. With specific regard
to throwing accuracy, the collective findings of included studies
investigating the effects of weighted balls on this variable imply
that 6 differently weighted balls have a negative effect on, or
induce no significant changes to, post–warm-up pitching accuracy. With the use of a wireless EMG device, it was also shown
that weighted balls induce varying muscular activation rates on
return to a regulation baseball (40), an effect that should be
closely considered in the design of chronic weighted baseball
throwing programs. Future research should also assess the impact
of various rest intervals post–weighted implement training
warm-up.
Two studies investigated the acute effects of weighted indoor
weight throw implements on indoor weight throw performance.
The indoor weight throw is an indoor track and field event,
similar to that of the hammer throw event that is performed in
the outdoor setting (19). These studies investigated the acute
effects of these implements, with both incorporating a control
condition (standard implement warm-up), on mean and peak
throw distance with the standard implement, and post–warmup fatigue. The procedure of both studies required subjects to
perform 5 one-heel turn throws with the randomly assigned
implement, followed by 3 maximal effort throws with the
standard implement. A 3-minute rest was completed between
each post–warm-up attempt.
Judge et al. (18) found that 5 throws with an overweighted
indoor weight throw implement weighing 1.37 kg (p 5 0.004) or
2.27 kg (p 5 0.027) heavier than standard male (11.4 kg) and
female (9.1 kg) implements significantly improved peak throw
distance compared with that of a standard implement condition.
Peak throw distance was the greatest distance thrown from 3
maximal effort throws with the standard implement, whereby a 3minute time interval elapsed between the intervention trials and
the postintervention trials, as well as between each postintervention trial. The 11.37 kg condition meant that the male
implement weight was 12.77 kg (12.02% weight increase),
whereas the female weight was 10.47 kg (15.05% weight increase). The 12.27 kg condition meant that the male implement
weight was 13.67 kg (19.91% weight increase), whereas the female weight was 11.37 kg (24.95% weight increase). The subject
cohort comprised of high school indoor weight throw athletes (n
5 10). There were no significant differences in peak distance
between the 2 overweighted conditions (p . 0.05). No significant
differences (p . 0.05) in mean throwing distance were evident
following throws with both overweighted conditions, although
mean distance was greatest following the 11.37 kg condition.
Although Judge et al. (18) found that the 11.37 kg (p 5 0.025)
2927
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Weighted Implement Training (2021) 35:10
Table 4
Acute effects of weighted bats on batting performance against a moving target.*
Reference
Sport
Subjects
Reyes and Dolny Baseball 19 collegiate players
(36)
Implements (% weight increase/
decrease from standard)
#WU trials; rest period between WU
and post-WU; post-WU intertrial rest
18 (3 sets 3 6 swings); 30 s; 30 s
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Nakamoto et al.
(31)
Baseball 8 male college
players
S 850 g (30 oz)
L 794 g (28 oz, 6.66% ↓)
H 1,531 g (54 oz, 80% ↑)
S 850 g (30 oz)
H 1,200 g (42.3 oz, 41%↑)
Ohta et al. (32)
Baseball 7 male college
players
S 850 g (30 oz)
H 1,200 g (42.3 oz, 41%↑)
Scott and Gray
(39)
Baseball E1: 30 experienced
players
E2: 20 experienced
players
E1: S 1,077 g (38 oz); L 794 g (28 oz, 30 (2 blocks of 15 swings); 5 min;
26.32% ↓); H 1,361 g (48 oz, 26.32% ↑) immediate
E2: S 794 g (28 oz); H 1,077 g (38 oz,
35.71% ↑)
3 or 6; 5 s; minimal
3; 5 s; minimal
Results and conclusions
No WU protocol significantly ↑ BV vs. all
other WU protocols but order of S-L-H
resulted in greatest BV↑
H produced marginally (p , 0.10)
significant ↑ in post-BV but ↓ temporal
accuracy; KA of bat weight but not bat
speed post–weighted warm-up
Performers cannot adequately exert
perceptual-motor control solely on the
basis of practice swings when interacting
with moving objects
Weighted tools are not recommended in
actual athletic situations
H produced greater bat speed during Vchanged condition
H induced greater timing errors in Vchanged condition (vs S), likely caused
by a decline in the ability to sufficiently
adjust or inhibit muscle activity to
correspond with altered target V
H ↓ the adjustment ability associated
with inhibition of muscle activation under
movement correction conditions
E1: Recalibration occurs between 5 and
10 “live” swings following a switch in
weighted bats; temporal accuracy
degraded
E2: Switching to H significantly ↑ timing
errors and significantly ↓ BV vs control
condition. Recalibration dependent on
the subjects’ own individual constraints
Overall: a sudden change in bat weight
negatively affects batting; recalibration of
perceptual-motor control cannot occur
solely on the basis of dry swings
*BV 5 bat velocity; WU 5 warm-up; S 5 standard bat; L 5 light bat; H 5 heavy bat; V 5 velocity; KA 5 kinesthetic aftereffect; ↑ 5 weight increase compared with study’s standard bat; ↓ 5 weight decrease
compared with study’s standard bat; E1 5 Experiment 1; E2 5 Experiment 2.
and 12.27 kg (p 5 0.007) resulted in significantly greater sensations of fatigue post–warm-up, resultant throw distance indicated that this did not degrade performance. Indeed, the lighter
of the 2 overweighted implements induced a 0.9-m increase in
peak throw distance compared with the standard implement. As
peak throw distance following throws with the standard implement was 14.15 m, the 0.9-m increase (6.36%) following the
lighter of the 2 overweighted implements may have considerable
performance implications in competition.
Bellar et al. (2) also found overweighted indoor weight
throw implements weighing 1.37 and 2.27 kg heavier than
standard male (15.87 kg) and female (9.07 kg) implements
significantly improved peak throw distance. The 11.37 kg
condition meant that the male implement weight was 17.24 kg
(8.63% weight increase), whereas the female weight was 10.44
kg (15.1% weight increase). The 12.27 kg condition meant
that the male implement weight was 18.14 kg (14.3% weight
increase), whereas the female weight was 11.34 kg (25.03%
weight increase). This study comprised of collegiate and elite
indoor weight throw athletes (n 5 17). The authors reported
that mean throw distance following the 11.37 kg condition (p
# 0.01, ES 5 1.49) and the 12.27 kg condition (p # 0.01, ES 5
1.09), compared with the standard warm-up, was significantly
greater during the first post–warm-up throw. The authors
reported an ES calculated in accordance with partial eta
squared (h2p ), which indicates the proportion of variance of the
dependent variable that is explained by the independent variable. A partial eta squared output (percentage of variance
explained) of $0.01–,0.06, $0.06–,0.138, or $0.138 indicates a small, medium, or large ES, respectively (34). Mean
throw distance of the second post–warm-up throw was also
significantly greater (p 5 0.007, ES 5 0.762) following the
11.37 kg implement warm-up condition compared with that
of the standard condition. Mean distance of all post–warm-up
throws was significantly lower (p , 0.02, ES . 0.8) following
the standard implement than the other conditions, with peak
post–warm-up throw distance being significantly greater than
the standard condition following the 11.37 kg (p , 0.002, ES
5 1.01) and 12.27 kg (p , 0.044, ES 5 0.619). No significant
differences were evident between the 2 overload warm-ups for
peak (p 5 0.768, ES 5 0.08) and mean (p . 0.05) throw
distance.
The findings of these studies imply that an overweighted implement warm-up enhances indoor weight throw performance
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among high school (18), and collegiate and elite (2), indoor
weight throwing athletes. Collectively, these studies imply that
the 11.37 kg implement (i.e., a 12.02 and 15.05% weight increase for male and female high school athletes, respectively, and
a 8.63 and 15.1% weight increase for male and female collegiate
and elite athletes, respectively) may induce greater performance
compared with the other implements, although the increases
following both overweighted warm-ups may result in significant
changes in the competitive setting.
Table 2 presents the included studies that investigated the acute
effects of underweighted and overweighted bats on performance
with a standard 30 oz bat (n 5 7). These studies included warmup implements ranging from 300 g (10.6 oz, 64.67% weight decrease) to 2,722 g (96 oz, 220% weight increase). All 7 studies
investigated the effects of such implements on bat velocity, with
additional variables measured including bat kinematic variables
such as peak bat acceleration and peak velocity (PV) at peak
acceleration (PA). Subjects were required to perform dry swings
or swings at a stationary target when performing swings post–
weighted bat warm-up.
DeRenne et al. (5,8,11) investigated the acute effects of a variety of overweighted and underweighted baseball bats on immediate bat velocity of a standard bat. The 1982 and 1992 studies
measured bat velocity with a photosensing computerized timer
(product manufacturer details not specified), whereas the 1986
study measured bat velocity with an accelerometer device
(product manufacturer details not specified) that was attached to
the barrel of the bat and an accompanying Bat Swing Profile
Computer. These studies consistently found the addition of a
donut ring to the standard bat produced the lowest bat velocity,
with said findings having implications for the addition of a weight
at the distal end of the bat. In addition, it was consistently found
that bats of minimal deviation from the standard bat weight
produced greatest bat velocities, leading to the recommendation
that slightly underweighted and overweighted bats (i.e., 612% of
a standard 850 g/30 oz baseball bat) may be optimal to immediately enhance bat velocity.
Higuchi et al. (15) found no significant change (p . 0.05) in
bat velocity following a standard bat warm-up condition
among 24 collegiate baseball players. Bat velocity was also
measured with a computerized photosensing timer device
(BatMaxx 5500; Technasport, MN). However, a significant
decrease in bat velocity (p , 0.05) was evident following an
overweighted bat warm-up (680 g/24 oz Pow’r Wrap). Although this finding of a negative impact of an overweighted bat
aligns with the work of DeRenne et al., numerous studies have
reported dissimilar results that contrast the recommendation
that bats should be 612% of a standard bat weight to enhance
bat velocity.
Szymanski et al. (45) found no significant differences (p .
0.05) in bat velocity of a standard bat following warm-up swings
with 10 differently weighted bats. In this study, bat velocity was
measured with a Setpro SPRT5A chronograph (Setpro; Westbrook, CT). Interestingly, Szymanski et al. found that the bats
that resulted in the greatest increases and decreases in bat velocity
were almost identical to that of DeRenne et al. Consequently,
because of a smaller subject cohort relative to the research of
DeRenne et al. (11), and consistent reports relating to the donut
producing the lowest bat velocities, Szymanski et al. concluded
that baseball players should avoid using distal loaded bats during
warm-ups. The authors also suggested that baseball batters
should abide by the guideline of using bats 612% of a standard
baseball bat weight.
Williams et al. (52) also found no statistically significant differences (p . 0.05) between standard, underweighted, and
overweighted warm-up conditions on various bat kinematics
among 15 National Collegiate Athletic Association (NCAA) Division 1 baseball players. A Vicon Nexus 3D motion capture
system (Oxford, United Kingdom) was used to record kinematics.
Bat kinematics included maximum resultant velocity (MRV),
resultant velocity at ball contact (RVBC), time difference between
MRV and RVBC, and bat angles at MRV and RVBC. The authors suggest that bats ranging from 301 g/10.6 oz to 1,576 g/
55.6 oz (64.66% weight decrease–85.33% weight increase) do
not alter bat swing kinematics. The authors also reported that
73.3% of subjects preferred warming up with the donut
attachment.
The study of Wilson et al. (53) exhibited similar findings to that
of Williams et al. (52) among 16 NCAA Division II baseball
players. Wilson et al. used a SwingProPlus chronograph (Athnetix, Inc., Arcade, New York, NY) to record various measures of
bat velocity and acceleration. The authors found no significant
effect (p . 0.05) of bat weight (standard, underweighted, and
multiple overweighted bats) on PV, PV at PA (PVPA), PA, and
time to PA of the standard bat. However, following pooling of the
data, a significant time effect was found (p # 0.05) for PV, PVPA,
and PA at certain time points post–warm-up. Peak velocity at
peak acceleration and PA were not significantly higher (p . 0.05)
1-minute post–warm-up but were significantly greater at 2 minutes (p # 0.05), with both values increasing significantly again at
4 and 8 minutes compared with 2 minutes (p # 0.05). Peak velocity significantly increased at 1 and 2 minutes post–warm-up (p
# 0.05), with further significant increases at 4 and 8 minutes
compared with 1-minute post–warm-up (p # 0.05). Peak velocity
at 8 minutes was also significantly greater than PV at 2 minutes (p
# 0.05). The authors concluded that batting performance peaked
between 4 and 8 minutes post–warm-up with various weighted
bats. This implies that batters should complete their warm-up
swings immediately on stepping into the on-deck circle and then
use the remaining time until at bat to analyze pitching patterns.
However, it is recommended that the reader remains aware of
existing criticisms within the literature relating to data pooling.
Jenkins (17) states that the pooling of data does not attribute
appropriate attention to the existence of variation within and
among individuals and likely increases the risk of a type 1 error;
that is, rejecting the null hypothesis when the null hypothesis is
true (i.e., stating that there is a difference when there is no
difference).
As the previous section detailed studies that used a standard
850 g (30 oz) bat, this section details the studies (n 5 7) that
investigated the acute effects of underweighted and overweighted
bats on batting performance with standard bats of different
weight (i.e., 822 g/29 oz–964 g/34 oz, excluding 850 g/30 oz)
(Table 3). These studies included warm-up implements ranging
from 113.40 g (4 oz, 87.5% weight decrease from the study’s 907
g/32 oz standard bat) to 2,722 g (96 oz, 317.39% weight increase
from the study’s 652 g/23 oz standard bat). All 7 studies investigated the effects of such implements on bat velocity, with
additional variables measured including resultant swing patterns
and subjects’ perceptions of bat weight and swing speed on return
to the standard bat.
Similar to DeRenne et al., Southard and Groomer (41) also
found the addition of a donut to a standard bat degraded bat
velocity (p , 0.001) of 10 experienced baseball players on return
to a standard bat. Bat velocity and joint kinematics were measured with a Watsmart Motion Analysis System (Northern
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Digital, Inc., Waterloo, ON, Canada). A reduced lag between the
lead elbow and wrist was revealed, corresponding to a lack of
velocity transfer from elbow to wrist. The authors suggest that
this alteration resulted in less effective organization of the kinetic
chain leading to a greater push motion that potentially contributed to the observed decrease in batting performance. This
formed the suggestion that bats with greater moments of inertia
alter swing patterns and degrade bat velocity, bolstering the
original recommendations of DeRenne et al. (5,8,11). Similar
findings were also reported by Montoya et al. (29), whereby an
underweighted bat and a standard bat produced significantly
faster bat velocities compared with an overweighted bat (p ,
0.05). Bat velocity was measured with a custom bat measurement
device consisting of 2 vertical photoelectric sensors (Model E3Z;
Omron Electronics, Schaumburg, IL).
Similarly, Miller et al. (26) found that bat velocity was significantly slower (p , 0.001) following an overweight condition
compared with that of a standard bat condition and an underweighted bat condition. Bat velocity was recorded with a Qualisys
3D motion analysis system (Oqus 210c; Qualisys Motion Technology, Göteborg, SE). No significant differences (p . 0.05) were
revealed between the effects of the standard and light bats on
post-test bat velocity. Bat velocity of swings post–heavy bat
conditions was significantly slower than pre–warm-up swings (p
, 0.05), with bat velocity following the light bat significantly
increasing from pre–warm-up to post–warm-up swings (p ,
0.001).
Kim and Hinrichs (21) found no main effect (p . 0.05) for any
of their warm-up conditions (standard bat, overweighted bat, and
arm weight condition) on bat velocity of a standard bat, which
was measured with an Advanced Motion Measurement–3D system (AMM-3D, Phoenix, AZ). However, the mean bat velocity of
the 20 baseball players (high school or college playing experience)
participating in the study decreased 0.203 6 3.83% following the
overweighted condition compared with pretest measures, a similar finding to that of Southard and Groomer (41). On further
analysis, it was found that bat velocity of the fourth trial following the overweighted bat condition was significantly higher
than the first post–warm-up trial (p , 0.05), suggesting that a rest
period of 3 minutes is necessary to observe an increase in bat
velocity above pre–warm-up velocity measures. The standard bat
warm-up also induced a similar immediate decrease in bat velocity (i.e., trial 1–trial 3) followed by a subsequent increase above
pre–warm-up values at trial 4. Bat velocity increases at this time
were greater than those exhibited at the same time point following
the weighted bat condition.
Szymanski et al. (44) reported no significant differences (p .
0.05) in bat velocity following warm-ups with 8 differently
weighted bats among a softball cohort, a similar finding to the
same research team’s aforementioned study with baseball
players (45). However, as per the conclusion of their previous
study, the authors concluded that softball players should avoid
adding the donut to their bat during warm-up swings as the
donut condition produced the slowest bat velocity in this
study. As in their previous study (45), bat velocity was measured with a Setpro SPRT5A chronograph (Setpro, Westbrook, CT).
In addition to investigating the acute effects of overweighted
bats on batting performance, 2 included studies also analyzed
subjects’ perceptions of bat speed and bat weight post–weighted
warm-up. Kim and Hinrichs (20) assessed the effects of various
weighted bats (standard, underweighted, and overweighted bats)
on standard bat velocity, as well as batters’ perceptions of swing
weight and swing speed on return to the standard bat. Bat velocity
was measured with a Vicon Nexus motion capture system (Oxford, United Kingdom). Although the 13 subjects (8 males and 5
females) experienced no significant differences in bat velocity
from pre-test to post-test following the overweighted bat warmup, subjects’ perceived bat speed during the post–warm-ups
swings to be faster following the overweighted condition compared with the other conditions.
Similar findings were also reported by Otsuji et al. (33). By
measuring bat velocity with 2 photoelectric switches (Model:
E3S-3L and EE3S-3D; Omron Ltd., Kyoto, Japan) and a digital
data recorder (Model: DR-M3a MK2; TEAC Ltd., Tokyo, Japan), the authors found no significant difference (p . 0.05) in
post–warm-up swing velocity following a standard bat condition
and an overweighted donut condition. However, bat velocity of
the first post-trial following the weighted warm-up was significantly slower (3.3%) than that of the standard condition (p ,
0.05) but returned to a similar level as the standard condition in
subsequent post-trials. Although such an absence of bat velocity
increases was exhibited, subjects perceived post–weighted bat
swing speed to be faster and bat weight to be lighter compared
with pre-test trials. The findings of these 2 studies indicate the
presence of a kinesthetic after effect (KA) following a weighted
bat warm-up. A kinesthetic after effect has been defined as the
perception of modification to a tool’s kinetic properties or perceptual distortion of limb position, movement, or intensity of
muscular contraction following the use of the previous implement
(31). A kinesthetic after effect has traditionally been considered
advantageous to batting performance and potentially gave rise to
the popularity of overweighted implements, such as the donut,
with the belief that its existence may lead to enhanced performance (11).
Table 4 details the studies that investigated the acute effects of
underweighted and overweighted bats on interceptive striking
performance with a moving target (n 5 4). The dynamic target of
these studies included a pitched baseball or the simulation of an
oncoming target, with weighted implements ranging from 794 g/
28 oz (6.66 and 26.32% weight decrease from the respective
studies’ standard implement) to 1,531 g/54 oz (80% weight increase from the respective study’s standard implement). All 4
studies investigated the effects of respective weighted implements
on bat velocity, with additional dependent variables including
temporal accuracy, spatial accuracy, swing onset time, subjects’
perceptions of bat speed and bat weight on return to the standard
bat, and upper limb muscular activity.
In a simulated baseball batting task involving a moving
target, Scott and Gray (39) investigated perceptual-motor
recalibration when switching between bats of varying weight.
The authors reported that although dynamic wielding of a new
tool following a change in implement results in immediate
recalibration when interacting with a stationary target, the
spatiotemporal demands of interacting with a moving target
may further diminish the efficacy of using weighted bats immediately before batting performance. Thus, as per the methodologies of the studies in the previous 2 subsections, Scott and
Gray (39) imply that the omission of a moving target in previous experimental designs does not sufficiently indicate how a
sudden change in bats of differing weight affects batting performance and the perceptual-motor system. Although many of
the 18 weighted bat studies included in this section were conducted at a time whereby technology may have not facilitated
the presentation of a moving target to subjects akin to those
that will be discussed in the current section, 14 of these studies
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required subjects to perform dry swings or strike a stationary
baseball during experimental trials (i.e., absence of a moving
target). Therefore, in their dual-experiment study, Scott and
Gray (39) had subjects face a computerized batting environment, which simulated a pitcher throwing an oncoming baseball toward the subject. A Fastrak positional tracker sensor
was placed on the end of the bat (Polhemus, VT) to determine
performance characteristics of each swing. Scott and Gray (39)
concluded that switching between bats of different weight results in an inability to recalibrate perceptual-motor control
solely on the basis of practice swings (i.e., the absence of batball contact and subsequent performance outcome) due to the
persistence of temporal errors. Although subjects recalibrated
within 5 (standard to underweighted), 10 (standard to overweighted), or 15 (underweighted to standard) “live” trials
(interaction with moving target) post–bat change, the inability
of the batter to perform live swings before approaching the
plate would result in timing errors of the initial pitches based
on this study’s results. The authors state that this is due to the
fact that until the action begins, the required adjustments on
return to the standard bat are variable and unknown, with
successful performance dependent on the athlete’s ability to
recalibrate the relationship between control (force and velocity
variables) and perceptual (timing and directional variables)
variables. The findings accentuated the importance of performance outcome feedback in the recalibration process when
switching between bats of different weight and the dependence
of the recalibration process on the subjects’ own individual
constraints or intrinsic dynamics (i.e., recommended bat
weight).
Similarly, Nakamoto et al. (31) investigated the influences of
subjective-objective mismatches in bat swings induced by the KA on
immediate batting performance against a simulated approaching
object. A horizontal trackway with 200 light emitting diodes simulated the continuous motion of the approach target, i.e., a baseball
(AO-5N model; Applied Office Co. Ltd., Tokyo, Japan). Kinematic
data of the bat were collected with a twentieth-camera digital 3dimensional motion analysis system (Motion Analysis Corporation,
Santa Rosa, CA). Although a KA of increased bat speed has traditionally been considered advantageous, the authors propose that due
to consistent reports of decreased bat velocity following overweighted bat warm-ups, subsequent performance with the standard
bat may be degraded as a result of actual and perceptual mismatches
of bat velocity. Such effects may result in delayed swing onset due to
the perception of enhanced bat velocity, mismatching actual decreases of this performance variable. Following a warm-up comprising of 3 swings with a standard bat, 3 swings with an
overweighted bat, or a recalibration warm-up comprising of 3
swings with the weighted bat before 3 swings with the standard bat,
subjects’ batting performance with the standard bat was analyzed
when interacting with a simulated oncoming target. Velocity of the
bat was collected with a 3D motion analysis system, with interceptive
timing performance being determined from the crossover point between the bat and the edge of the trackway. Citing the relatively
short-term effect of the KA, Nakamoto et al. used a shorter rest
period between weighted bat swings and standard bat swings (,5
seconds) than that of Scott and Gray (39) (5 minutes). Findings
indicated a KA of bat weight, but not of bat speed (i.e., actual and
perceptual measures of bat speed post–weighted bat increased), with
the recalibration warm-up resulting in no change to said perceptions.
Although the recalibration warm-up induced smaller absolute temporal errors (ATE) compared with the weighted (p , 0.05) and
normal (p , 0.01) conditions in an unchanged-velocity condition;
the use of a weighted bat induced significantly greater timing errors
(p , 0.05) in a target velocity-changed condition compared with a
standard bat warm-up, similar to that of Scott and Gray (39). As no
spatial errors were evident, results indicated that the use of a
weighted bat had a selective effect on perceptual-motor control requiring movement timing correction.
In reference to the claims in previous studies that weighted
bat warm-ups may increase intrinsic muscle contractile
properties (e.g., 36), Nakamoto et al. (31) state that the observed selective effect diminishes the efficacy of these prior
suggestions as such performance improvements resulting from
increased contractile capabilities would be evident regardless
of stimulus condition (i.e., spatial or temporal changes of the
oncoming target). The authors, therefore, postulated that
weighted bat warm-ups affect the central nervous system
(CNS), but not the peripheral system, in interceptive striking
actions with a moving target. In reference to computational
theory, and the reliance on predictive mechanisms to correct
movement due to the rapid nature of interceptive striking
tasks, Nakamoto et al. (31) suggest that weighted bat warmups result in the inability of batters to correctly alter swing
performance during a velocity-changed task due to inadequate
error detection contributing to the distortion of the efference
copy. As evident in their results, this produces faster swings
and larger timing errors, as well as inducing motor programming errors resulting in such movements that could not
be adjusted online. Thus, the authors conclude that weighted
bat warm-ups negatively affect the performance of motor
skills that greatly rely on anticipation and that practice swings
alone are not sufficient to recalibrate and exert effective
perceptual-motor control during a dynamic interceptive
striking action.
With the same experimental design as their previous study
(31), the same research team (32) completed a follow-up study
that investigated the effects of a weighted bat warm-up on bat
velocity, subjects’ perceptions of bat weight and speed, temporal and spatial accuracy, as well as upper limb muscle activity during post–warm-up swings with a standard bat.
Muscle activity was measured with an EMG device (SynaAct
MT-11; NEC Sanei Inc., Japan), whereby bipolar surface
electrodes were placed parallel to muscle fibers on the muscle
belly of the right and left pectoralis major, biceps brachii, triceps brachii, flexor carpi radialis, and the extensor carpi
ulnaris. Subjects performed 3 maximal effort swings with either a standard bat or an overweighted bat. This study supported the previous findings (31) as the weighted bat resulted
in the perception of increased bat velocity and decreased bat
weight, with neither warm-up implement degrading spatial
accuracy (i.e., location-changed condition). Swing velocity for
both warm-up conditions was significantly lower in the
velocity-changed condition compared with the unchanged
condition (p 5 0.019, d 5 3.18). However, in line with subjects’ perceptions of bat speed, bat velocity in each of the 3
conditions was faster following the weighted bat warm-up,
replicating the finding of the previous study (31). Although
there were no significant differences (p . 0.05) in ATE in the
velocity-changed condition following either the weighted or
normal warm-up, the greater ES (d 5 1.61) pertaining to ATE
following the weighted condition illuminated a negative effect
of the use of the overweighted bat during warm-up swings
(i.e., decreased temporal accuracy). The authors used an ES
index calculated in accordance with Cohen’s d index. Following the weighted warm-up, significantly greater ATE was
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evident in the velocity-changed condition compared with the
unchanged condition (p 5 0.024, d 5 3.48) and the locationchanged condition (p 5 0.001, d 5 2.79). There was no significant effect (p . 0.05) of the weighted bat warm-up on
muscle activity before ball impact during the velocity or spatial
changed conditions compared with the unchanged condition.
In the velocity-changed condition post–weighted warm-up,
subjects coordinated decreased bat velocity to accommodate the
change in target velocity by inhibiting extensor carpi ulnaris
(ECU) activity. This muscle functions in ulnar flexion of the wrist,
thus aiding bat velocity. However, a lower degree of difference in
ECU activity between the velocity-changed and unchanged condition was evident following the weighted warm-up (5.9% 6
7.40) compared with the standard warm-up (12% 6 4.16). These
findings suggest that overweighted bats result in an acute decline
in the adjustment ability of muscle activity as ECU activity is
insufficiently inhibited to correspond to a change in target velocity. Although this supports their previous findings that suggested weighted bat warm-ups affect the CNS (31), the authors
state that they were unable to dismiss the potential of inducing a
potentiation effect due to the use of an overweighted bat warmup. However, corresponding to the absence of significant increases of muscle activity post–weighted bat warm-up, it was
postulated that the spatiotemporal demands and accompanying
uncertainty of oncoming target trajectory and velocity likely
resulted in submaximal effort swings, thus decreasing the likely
expression of potentiated neuromuscular performance. Consequently, the authors conclude that weighted bat warm-ups affect
coincident timing performance in tasks involving a velocity
change due to CNS interference as indicated by a decline in the
ability to sufficiently adjust or inhibit muscle activity. Such implements do not result in peripheral system interference as indicated by an absence of significant differences in EMG measures,
a potential result of subsequent submaximal effort swings to
correspond with the spatiotemporal demands of an oncoming
target.
With the inclusion of a moving target in post–weighted bat
trials, Reyes and Dolny (36) assessed the acute effects of various
warm-up procedures comprising a standard bat, an underweighted bat, and an overweighted bat. Interestingly, this study
found a warm-up protocol following the order of standard-lightheavy produced the greatest bat velocity increase (6.03%), followed by a protocol comprising solely of heavy bat swings
(15.08%). Bat velocity was measured with 2 infrared photocell
control boxes (Model #63504, Lafayette Instrument, Lafayette,
IN) and a multifunction timer (Model #54035A; Lafayette Instrument, Lafayette, IN). However, as per the acknowledgment of
Scott and Gray (39), performance accuracy was not measured
with no reports of experimental trial swing errors included. The
findings of Nakamoto et al. (31), Ohta et al. (32), and Scott and
Gray (39) collectively imply that although overweighted bats
potentially increase bat velocity, temporal accuracy reductions
leading to degraded performance are likely to occur.
This review process identified that studies investigating the
acute effects of weighted implements on interceptive striking
are conducted almost exclusively in the baseball domain. Of
the 18 included studies in this section, 17 investigated the effects of weighted bats on baseball batting performance. This
emphasizes an absence of research into the acute effects of
other weighted implements that may aid interceptive striking
actions, such as weighted golf clubs, weighted hockey sticks,
and weighted racquets. In relation to studies included in this
section, this review provides further support to the
recommendations of DeRenne et al. (11) to use bats within
612% of a standard 30 oz bat. In particular, distal loaded
tools (for example, the donut) and bats with increased moments of inertia consistently resulted in decreased bat velocity,
altered swing patterns, and inaccurate perceptions of bat velocity and weight on return to the standard bat. There are a
limited number of studies investigating the acute effects of
overweighted bats that have exhibited the potential to increase
bat velocity; in contrast, such tools negatively impact interceptive striking of a dynamic target due to the creation and
persistence of temporal accuracy errors that are not modulated
by dynamic wielding of the standard tool. Because of the range
of included weighted implements, and variation in weight of
regulation bats permitted among baseball populations, results
of these studies warrant careful consideration. As per the cohorts of the respective studies, some subjects may have been
using a standard bat that was overweighted compared with
their respective bat in competition. Therefore, it is recommended that, if feasible, practitioners determine the effects of
respective weighted bats on each individual’s batting performance. However, because of the inability of batters to practice
live performance before taking the field, the ineffectiveness of
dynamic wielding as shown in this review sheds light on the
potential negative effects of overweighted bats. These studies
(31,32,39) highlight the implications of previous studies that
did not include a moving target and the subsequent effects of
these implements on markers of performance beyond bat velocity, muscular activation, and batters’ perceptions of bat
properties and speed. However, future research is warranted
that further investigates the acute effects of underweighted bats
on interceptive striking of a dynamic target.
Multiple studies included in this review have made suggestions as to the underlying mechanisms responsible for the
justification of using weighted implements as a warm-up
strategy and the observed effects on return to the standard
implement. Based on their findings, Van Huss et al. (50) suggested the use of overweighted implements increases motor
unit activation, with Morimoto et al. (30) suggesting the use of
underweighted implements results in enhanced neuromuscular
activity. Wilson et al. (53) suggested that Banister Fitness Fatigue Model may sufficiently explain their findings as the
greatest increases in batting performance were observed between 4 and 8 minutes. This model proposes that performance
is a balance between fitness and fatigue, whereby changes to
the former outlast those of the latter following recent contractile activity (23). This implies that maximal performance
does not occur immediately following the training stimulus,
thus explaining the delayed enhancement of performance following a weighted implement protocol as exhibited in the
study of Wilson et al. (53). This model may also explain the
findings of other included studies who experienced similar
delayed performance enhancements (21,50).
Wilson et al. (53) also referred to the possible elicitation of
postactivation potentiation (PAP) following the use of overweighted bats as a potential mechanism for subsequent performance. Indeed, Judge et al. (18) and Bellar et al. (2) attributed
observed performance increases to this phenomenon following
their investigations into the acute effects of overweighted indoor
weight throw implements. Postactivation potentiation is defined
as the transient increase in short-duration contractile force capabilities of a high-velocity, short-duration competitive movement as a result of previous contractile activity of relatively higher
intensity (27). This phenomenon has been suggested as the most
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appropriate physiological evidence of the acute effects of the
fitness-fatigue model (23). Specifically, the realization of PAP
is a function of the net balance between potentiation and fatigue, subsequent to the imposed conditioning activity (37). In
reference to previous studies (29,45), Wilson et al. identified
the studies’ short rest periods as a likely factor in the absence of
improved performance following the weighted implement
warm-up protocols. Had these aforementioned studies included greater rest times such as those of Wilson et al. (53) (4–8
minutes) and Kim and Hinrichs (21) ($3 minutes), improved
performance may have been observed. Wilson et al. (53) state
that the #1-minute rest periods of these studies would have
resulted in any existing potentiation being dominated by fatigue within the respective time frame as per the fitness-fatigue
model. In the performance environment, however, predicting
when the respective individual’s at-bat will take place to begin
weighted bat warm-up swings may not be practical due to the
unpredictable nature of the preceding batter’s at-bat situation.
As highlighted by Wilson et al., coaches often advise batters to
initially take some pitches during their at-bat to identify the
types of pitches the pitcher is throwing. This, therefore, adds to
the variability in time the preceding batter may spend at-bat,
and varies the time the subsequent batter may spend in the ondeck circle. As a result of this, exploring different time periods
in which to begin weighted bat swings in the on-deck circle,
within the time frame of the time periods that facilitate improved performance as identified by Wilson et al. (53) and Kim
and Hinrichs (21) (i.e., $3 minutes or 4–8 minutes), is suggested (53).
As verification of PAP requires observation of increased peak
twitch force/torque and increased rate of twitch force/torque development, which are verified via electrical stimulation of single
muscles/muscle groups (3,24,35), it may, however, be suggested
that Banister model (23) and postactivation performance enhancement (PAPE) (35) are the most appropriate explanations of
the acute effects of weighted implements based on the recommended mechanisms of the included studies. However, although
these models may sufficiently explain reports of enhanced batting
performance following a weighted bat warm-up in studies using a
stationary target, the findings of studies assessing such effects
when intercepting a dynamic target potentially diminish the efficacy of attaining such potentiated peripheral states. Ohta et al.
(32) state that because of the spatiotemporal demands in live
batting environments (i.e., with a moving target), it is likely that
batters correspondingly perform submaximal effort swings, thus
alleviating the likelihood of expressing such potentiated efforts.
The conclusions of the included studies collectively highlight
varying suggestions as to the underlying mechanisms of
weighted implement training and accompanying effects on immediate performance. Therefore, future research is necessary to
identify these underlying mechanisms and the efficacy of their
elicitation in representative task designs, particularly in interceptive striking sports. An investigation into the interaction of
such mechanisms and various rest periods should also be conducted to aid weighted implement warm-up design and further
the field’s understanding of their acute effects on sports
performance.
This systematic review highlights an overriding, and almost
exclusive, prevalence for investigating the acute effects of
weighted baseball implements on the sport’s respective motor
skills (i.e., batting and pitching). This highlights a need for future
research to investigate the acute effects of weighted balls on respective motor skills in other sports such as soccer, rugby,
basketball, golf, and American football. It also revealed a need for
future research to assess the acute effects of weighted implements
on interceptive striking performance in other sports, such as golf,
field hockey, ice hockey, and all racket-based sports. Such insights
will inform and expand weighted implement training literature, as
well as potentially facilitate the design of preparatory strategies to
enhance immediate performance with the respective standard
competitive implement.
Although the use of weighted implements in preparation for
competition has traditionally been considered advantageous,
this review highlights both positive and negative implications
of their use immediately before competitive performance.
From the limited number of studies investigating the acute
effects of weighted balls on pitching and bowling performance, findings indicate that, in certain conditions (consideration of weight of modified implement, volume of
repetitions performed, and time interval between weighted
and standard implement repetitions), there is potential for
enhanced pitching velocity. However, consideration for the
effect of weighted implements on pitching accuracy is required. The 4 studies that assessed the acute effects of
weighted implements on pitching and bowling accuracy
reported an absence of significant change or a detrimental
effect on throwing accuracy. The 2 studies investigating the
acute effects of weighted indoor weight throw implements on
indoor weight throw performance imply that positive effects
on subsequent standard implement throw distance may be
realized. However, there is a need for future research to expand the weighted implement training research among the
track and field events and to identify the optimal programming of these implements indicating the optimal weight,
repetitions, and rest times needed to realize significant improvements in performance. In contrast, research investigating the acute effects of weighted bats on batting
performance is more ambiguous with various studies inferring
negative effects of such implements. The use of overweighted
bats has consistently been demonstrated to negatively impact
bat velocity and overall batting performance, with further
suggestions that bats of greater moments of inertia (distal
loaded) negatively affect bat velocity and swing patterns (41).
Furthermore, their effects on immediate motor skill performance may not be isolated to objective measures of performance but may also influence batters’ perceptions of
regulation bat swing speed and heaviness, potentially resulting in an objective-subjective mismatch (a kinesthetic after
effect) that has been shown to have detrimental effects on
batting success. Existing literature has identified the need for
live swings to immediately recalibrate to the standard bat so
that potential enhancements in batting performance following
a weighted bat protocol can be realized (31,39). Consequently, these studies suggest that the use of weighted implements before competitive performance is not recommended.
This finding has implications for future experimental designs
when investigating interceptive striking performance in sports
with spatiotemporal demands due to the prominence of
moving targets. However, 7 of the 12 studies (58%) that included an underweighted bat found significant increases in
standard bat velocity with bats as light as 6.4 oz (26,29). It is,
therefore, recommended that more representative experimental set-ups similar to those of Nakamoto et al. (31), Ohta
et al. (32) and Scott and Gray (39), be used to further investigate the acute effects of underweighted bats on batting
performance with coincident timing demands.
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Weighted Implement Training (2021) 35:10
Practical Applications
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The findings of this systematic review suggest that particular
weighted implements induce acute performance increases in
subsequent performance using the standard competition
implement. For example, in athletics, the use of 11.37 and
12.27 kg overweighted implements immediately before
competition may facilitate increased throw distance among
high school, collegiate, and elite athletes, that is, 12.77 and
13.67 kg for male high school athletes, 17.24 and 18.14 kg
for male collegiate and elite athletes, 10.47 and 11.37 kg for
female high school athletes, and 10.44 and 11.34 kg for female collegiate and elite athletes. Although both overweighted implements improve throw distance, the 11.37 kg
implement may produce optimal results. With regard to
weighted bats, the results of this review suggest that the use
of underweighted bats, as light as 181 g (6.4 oz) and 272 g
(9.6 oz), may increase subsequent standard bat velocity.
However, further research is needed to investigate the acute
effects of warm-up swings with an underweighted bat on
standard bat performance when attempting to intercept a
dynamic target (i.e., a pitched baseball). Pitching weighted
baseballs before competitive pitching performance may increase pitched-ball velocity, but careful consideration should
be given to its potential negative effects on pitching accuracy.
Additional consideration, on the part of the strength and
conditioning coach or skill acquisition specialist, should also
be given to each individual’s strength level as it is suggested
that this is an important variable to assess when considering
the efficacy of using weighted implements as a warm-up
strategy (2,18).
Acknowledgments
No external sources of funding were provided during this
research. The authors report no conflict of interest.
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