IJSM/4990/9.10.2015/MPS
Training & Testing
Low-load Slow Movement Squat Training Increases
Muscle Size and Strength but Not Power
Authors
S. Usui1, S. Maeo2,3, K. Tayashiki1, M. Nakatani1, H. Kanehisa1
Affiliations
1
Key words
▶ movement speed
●
▶ task-specificity
●
▶ explosive power
●
▶ rate of electromyography
●
rise
Abstract
Sports and Life Science, National Institute of Fitness and Sports in Kanoya,
Faculty of Sport Sciences, Waseda University, Tokorozawa, Japan
3
Japan Society for the Promotion of Science, Tokyo, Japan
▼
We tested a hypothesis that low-load squat training with slow movement and tonic force generation (LST) would increase muscle size and
strength but not necessarily power. Healthy
young men were assigned to LST [50 % one-repetition maximum (1-RM) load, 3 s for lowering/
lifting without pause: n = 9] or low-load normal
speed (LN: 50 % 1-RM load, 1 s for lowering/lifting
with 1-s pause; n = 7) groups. Both groups underwent an 8-week squat training program (10 repetitions/set, 3 sets/day, and 3 days/week) using
the assigned methods. Before and after the intervention, quadriceps femoris muscle thickness,
maximal torque during isometric hip extension
Introduction
▼
accepted after revision
September 21, 2015
Bibliography
DOI http://dx.doi.org/
10.1055/s-0035-1564255
Published online: 2015
Int J Sports Med
© Georg Thieme
Verlag KG Stuttgart · New York
ISSN 0172-4622
Correspondence
Dr. Sumiaki Maeo
Faculty of Sport Sciences
Waseda University
2-579-15 Mikajima
Tokorozawa
Japan 359-1192
Tel.: + 81/90/3328 6698
Fax: + 81/994/46 4932
smaeo1985@gmail.com
Resistance training has been popular not only
among athletes but also in a wide spectrum of
individuals, regardless of sex or age, because of its
beneficial impact on sports performance and
quality of life [4, 10]. In general, using high-load
resistance training [> 70 % one-repetition maximum (1-RM)] has been regarded as optimal for
gaining muscular size and strength [4]. However,
such a training regimen is not always recommended for, or favored by, some individuals due
to the high level of mechanical stress and potential risk of injuries [20]. In addition, a marked
increase in systolic blood pressure (up to
250 mmHg) has been reported to occur during
high-load resistance training for large muscle
groups [16], which is strongly associated with
the risk of exercise-related accidents, including
death from cardiovascular as well as noncardiovascular causes, especially in elderly populations
[15, 19]. Therefore, developing a resistance training regimen that can produce substantial gains in
strength with much reduced mechanical stress is
to be considered [27].
and knee extension, 1-RM squat, lifting power
from squatting position and rate of electromyography rise (RER) in knee extensors during the
task, leg extension power and vertical jump
height were measured. After the intervention,
the LN group showed no changes in all the variables. The LST group significantly (P < 0.05)
increased muscle thickness (6–10 %), isometric
hip extension torque (18 %) and 1-RM squat
(10 %), but not isometric knee extension torque,
lifting power and RER, leg extension power and
vertical jump height. These results suggest that
LST can increase muscle size and task-related
strength, but has little effect on power production during dynamic explosive movements.
As an approach to the training regimen mentioned above, Tanimoto and Ishii [27] reported
that relatively low-load (~50 % 1-RM) resistance
training with slow movement and tonic force
generation (3 s for lowering and lifting actions
without a relaxing or pause phase, designated
as LST) in knee extension caused significant
increases in muscle size and strength in young
men. In that prior study, the gains in muscle size
and strength after LST were comparable to those
observed after traditional high-load (~80 % 1-RM)
resistance training performed at a normal speed
(1 s for lowering and lifting actions and a 1-s
relaxation or pause phase) [27]. In addition, an
increase in systolic blood pressure during LST
was shown to be not as high (less than 200 mmHg)
as traditional high-load resistance training [27].
These results suggest that LST can be considered
one of the useful methods of resistance training
for promoting muscle hypertrophy and strength
gain and is a method that is relatively safe for a
wide range of populations. However, no studies
have investigated the effect of LST on power production capability during whole-body or multijoint dynamic movements, which is the most
Usui S et al. Low-load Slow Movement Squat … Int J Sports Med
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2
important neuromuscular function in various physical activities
and also contributes to reducing the incidence of falling or slipping, especially in elderly populations [2].
Tanimoto et al. [26] also observed that a 13-week LST program in
the leg muscles changed muscle activation and force generation
patterns during dynamic (cycling) movements to be more tonic.
This suggests that LST may have unfavorable effects on dynamic
power production, since more instantaneous (i. e., less tonic)
muscle activation is important for achieving high power [1],
especially during dynamic explosive movements. Additionally,
Kanehisa and Miyashita [18] reported that slow speed resistance
training had little effect on power production during high-speed
movements. Considering these factors, it is possible that LST
would increase muscle size and strength, but not necessarily
power during dynamic explosive movements due to the taskspecific adaptation to the training modality (i. e., slow speed and
tonic force generation). The purpose of this study was therefore
to examine the effect of LST on muscle size and function, with
the specific emphasis on explosive power production during
whole-body or multi-joint dynamic movements. We hypothesized that LST would increase muscle size and strength but have
little, if any, effect on power production during dynamic explosive movements.
Methods
▼
Subjects
16 healthy young men voluntarily participated in this study. The
subjects were randomly assigned to either LST (n = 9) or lowload normal speed (LN: n = 7) group. The means and standard
deviations (SDs) of age, body height and body weight were
22.2 ± 2.1 years, 175.0 ± 7.2 cm and 71.6 ± 5.8 kg for the LST group,
and 22.5 ± 0.5 years, 169.4 ± 4.7 cm and 68.7 ± 5.2 kg for the LN
group, respectively. The subjects were habitually active, but
none were involved in any type of exercise program ( ≥ 30 min/
day, ≥ 2 days/week). None had experienced a systematic resistance training program within one year before the onset of the
study. This study was approved by the local ethics committee
and was conducted in accordance with the ethical standards of
the International Journal of Sports Medicine [17]. The subjects
visited the laboratory, and were fully informed about the purpose, procedures and possible risks involved in the study, and
provided written informed consent.
Training program
Both groups underwent a parallel squat training program with
50 % 1-RM load, 10 repetitions/set, 3 sets/day, 3 days/week, for 8
weeks using the following methods; LST: 3-s lowering and 3-s
lifting without a pause phase, LN: 1-s lowering and 1-s lifting
with 1-s pause phase [26]. Subjects in each group repeated the
movement at approximately constant speed and frequency with
the aid of a metronome. A rest period of 1 min was taken
between the sets. For the first and second week of the training
period, the exercise load (50 % 1-RM) was based on the 1-RM for
each subject measured at the pre-training measurement
(explained in the 1-RM squat section below in detail). 1-RM
squat was measured at the start of the third week and at every 2
weeks thereafter (i. e., at the start of the first session of the third,
fifth and seventh weeks), and the exercise load (50 % 1-RM) was
adjusted for each subject on the basis of the measured 1-RM
value. In the training sessions, that included a 1-RM measureUsui S et al. Low-load Slow Movement Squat … Int J Sports Med
IJSM/4990/9.10.2015/MPS
ment, a rest period of at least 10 min was set before starting the
prescribed exercise tasks (LST or LN).
Measurements
Before and after the training intervention, the following variables were measured.
Muscle thickness
Muscle thickness of the 4 muscles composing the quadriceps
femoris of the right side was measured by a B-mode ultrasound
(Prosound α6; Aloka, Tokyo, Japan) with a linear scanner. The
measurement sites were 30, 50 and 70 % of the femur (the distance from the great trochanter to articular cleft between the
femur and tibia condyles) for the rectus femoris (RF) and the
vastus intermedius (VI), and 50 % for the vastus lateralis (VL) and
the vastus medialis (VM). During the measurements, the subjects stood upright with their arms and legs relaxed extended
position (i. e., the anatomical position). In accordance with a procedure described in an earlier study [3], the measurement sites
were precisely located and marked at the anterior surface of the
femur length. A transducer with a 7.5 MHz scanning head was
placed perpendicular to the underlying muscle and bone tissues.
The scanning head was coated with water-soluble transmission
gel, which provided acoustic contact without depressing the
dermal surface. The obtained cross-sectional ultrasonographic
images were printed out by an echo copier. The muscle thickness
was measured as the distance between the fat-muscle tissue and
muscle-bone interfaces (for the VI, between bone and its superficial aponeurosis).
Isometric torque
Torque during maximal voluntary isometric hip extension and
knee extension of the right leg was measured using an isokinetic
dynamometer (Biodex system2; Biodex Medical Systems, NY,
USA). In the hip extension torque measurements, the subjects
lay supine on an adjustable seat, and the torso was held tightly
▶ Fig. 1a). The hip extension/flexion attachment was
in the seat (●
set and isometric hip extension torque was measured at 90 ° (full
extension: 0 °) of the hip joint with the knee joint kept at 90 °
(full extension: 0 °). In the knee extension torque measurements,
the subjects sat on the seat with support for the back and hips,
▶ Fig. 1b).
and the hip joint was kept at 90 ° (full extension: 0 °) (●
The torso was held tightly in the seat. The knee extension/flexion attachment was set and isometric knee extension torque
was measured at 90 ° of the knee joint. After a sufficient period
of warm-up, the subjects were asked to perform maximal isometric hip extension and knee extension twice for each task.
Additional trials were performed if the difference in the peak
torque of the 2 trials in each task was more than 10 %. A rest
period of more than 2 min was taken between trials. In each task,
the highest value of the peak torque was selected for analysis.
1-RM squat
1-RM parallel squat was measured with the same bar and weight
▶ Fig. 1c). As a warm-up,
plates used in the training regimen (●
the subjects performed squat several times with the load 80 % of
the body weight. Subsequently, 5–10 kg weight plates were
gradually added with at least 2-min interval between trials, and
the maximal load lifted was determined as 1-RM.
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Training & Testing
IJSM/4990/9.10.2015/MPS
a
b
c
d
e
f
Fig. 1 Pictures of the muscle function measurements; isometric hip extension torque a, isometric knee extension torque b, 1-RM of squat c, lifting power
d, leg extension power e and squat and counter-movement jump height f. Informed consent for the use of the pictures was obtained.
Lifting power and rate of electromyography rise
Maximal lifting power from squatting position was measured
▶ Fig.
using a custom-made lifting power measurement device (●
1d). In this system, the bar was connected to the platform with
the slings, and the load on the bar was adjusted on-line. From a
parallel squatting position, the subjects tried to lift (stand up
against) the bar on the shoulder as fast as possible, with the load
100 % of the body weight (e. g., a 70 kg person lifted a 70 kg load).
From lifting velocity data measured by an accelerometer set in
the platform, maximal lifting power was calculated by the following equation.
Power (W) = m × v × g
where m is body weight (kg) of each subject (i. e., lifting load), v
is peak lifting velocity (m/s), and g is gravitational acceleration
(9.8 m/s2). After a sufficient warm-up and practice, the subjects
performed the task twice with an interval of at least 30 s. Additional trials were performed if the difference in the maximal
power of the 2 trials was more than 10 %. The highest value of
the peak power was selected for analysis.
During the task, surface electromyograms (EMGs) were recorded
from the RF, VL, and VM muscles using a bipolar configuration.
The bipolar Ag-AgCl electrodes (diameter, 8 mm; interelectrode
distance, 20 mm) were placed over the bellies of those muscles
after the skin surface was shaved, rubbed with sandpaper and
cleaned with alcohol. All electrode positions were carefully
measured in each subject to ensure identical pre- and posttraining recording sites. The electrodes were connected to a differential amplifier (gain × 1000, Common-mode rejection
ratio > 80 dB, input impedance > 100 MΩ, model MEG-6100;
Nihon-Kohden, Tokyo, Japan) having a bandwidth of 5–1 000 Hz.
The EMG and lifting velocity data were synchronized and
obtained at a sampling rate of 1 000 Hz using a 16-bit A/D converter (Power Lab 16 s; ADInstruments, Sydney, Australia), and
stored on a personal computer. During the off-line analysis using
software (Chart version 7; ADInstruments, Sydney, Australia),
the EMG signals were digitally high-pass filtered by using a
fourth-order, zero-lag Butterworth filter with a 5-Hz cutoff frequency, followed by a moving root-mean-square filter with a
time constant of 50 ms [2]. EMG onset was identified as the time
point at which the amplitude of the EMG increased by a magnitude of 2 standard deviations (SDs) of the resting EMG. From the
EMG data of the trial in which maximal lifting power was
obtained for each subject, rate of EMG rise (RER), determined as
the slope (ΔEMG/Δtime) of the filtered EMG signal, was calculated and peak value observed during the trial was adopted as
maximal RER.
Leg extension power
Maximal leg extension power was measured using an isokinetic
leg extension dynamometer (Kick-Force; Takei, Tokyo, Japan,
▶ Fig. 1e). The subjects sat on the seat with support for the back,
●
and the torso was held tightly in the seat. From the hip- and
knee-flexed position both at 90 °, maximal leg extension power
at a velocity of 0.8 m/s was measured. The trials were repeated 5
times with an interval of at least 10 s, and the highest value was
adopted as the maximal leg extension power.
Squat and counter-movement jump height
Squat and counter-movement jump height was measured by the
use of a mat switch platform (Multi Jump Tester; DKH, Tokyo,
▶ Fig. 1f) [25]. In this system, the jump height was calcuJapan, ●
lated based on the subject’s flight time. The participants were in
a standing position, and performed squat and counter-movement jumps as high as possible. The position of the jumper on
the mat was the same for takeoff and in landing. When jumping,
the participants kept their hands on their hips and jumped vertically with (counter-movement jump) or without (squat jump)
counter-movement on the mat switch platform. The participants completed 3 trials for each task with a rest interval of at
Usui S et al. Low-load Slow Movement Squat … Int J Sports Med
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Training & Testing
IJSM/4990/9.10.2015/MPS
Training & Testing
least 10 s between the trials. The highest value for the 3 trials for
each task was used for analysis.
lyzed using SPSS software (version 20.0; IBM Corp., Armonk,
N.Y., USA).
Reproducibility of the measurements
Results
Day-to-day (separated by 3–5 days) reproducibility of the measurements was examined on 6 healthy men (age: 22.3 ± 2.7 years,
height: 169.4 ± 4.8 cm, body weight: 70.3 ± 5.7 kg) for the muscle
thickness and function (strength and power) variables. Paired
t-tests revealed no significant differences between days in all the
variables. The coefficient of variation (CV) and the intraclass correlation coefficient (ICC) for each measurement variable were
▶ Table 1). The
less than 4.3 % and more than 0.80, respectively (●
magnitude of ICC was higher than 0.75, which is considered the
threshold for reliability [28].
▼
No significant baseline differences were found in all the variables (P > 0.05) except for lifting power and counter-movement
jump height, which were higher in the LST than the LN group.
The following shows the changes in each variable after the intervention.
Muscle thickness
▶ Fig. 2 shows the changes in the muscle thickness for both
●
Normality of the data was checked and subsequently confirmed
using the Kolmogorov-Smirnov test. Descriptive data are presented as mean ± SD. An unpaired Student’s t-test was used to
test the baseline difference between groups. A paired Student’s
t-test was used to test the difference between pre- and post-test
for each group. In addition, relative changes ( %) in the strength/
power variables for each subject were calculated and compared
between the variables by a one-way repeated measures analysis
of variance followed by post hoc comparisons (Tukey’s test) to
test the difference in the training-induced changes in the variables. A significance level was set at P < 0.05. All data were ana-
Isometric torque
▶ Fig. 3 (LST) and ●
▶ Fig. 4 (LN) shows the changes in the strength/
●
power variables. The LST group significantly increased the iso▶ Fig. 3a), but no
metric hip extension torque (+ 18 %, P = 0.006, ●
▶ Fig. 3a).
change was observed in the knee extension torque (●
The LN group did not show any significant changes in the hip
▶ Fig. 4a).
extension torque and knee extension torque (●
1-RM squat
The LST group significantly increased the 1-RM squat ( + 10 %,
▶ Fig. 3b). No change was observed in the LN group
P = 0.01, ●
▶ Fig. 4b).
(●
Table 1 The coefficient of variations (CVs) and intraclass correlation coefficients (ICCs) of the variables in between-day measurements (n = 6).
Dependent variables
CV (%)
ICC
Muscle thickness
Isometric hip extension torque
Isometric knee extension torque
1RM of squat
Lifting power
Leg extension power
Squat jump height
Counter-movement jump height
1.0–2.9
2.3
3.0
1.9
4.3
0.8
1.8
2.1
0.80–0.96
0.98
0.98
0.96
0.83
0.99
0.96
0.92
Lifting power and RER
▶ Fig. 3c)
Lifting power did not significantly change in the LST (●
▶ Fig. 4c). Maximal RER also did not show any
and LN group (●
significant changes in all the muscles in both groups (LST: RF;
3 320 ± 1 631 μV/s at pre vs. 3 491 ± 1 923 μV/s at post, VL;
6 078 ± 2 072 vs. 5 590 ± 2 844 μV/s, VM; 6 801 ± 3 312 vs.
5 995 ± 3 609 μV/s, LN: RF; 4 209 ± 1 802 vs. 3 701 ± 2 218 μV/s, VL;
7 118 ± 3 207 vs. 7 845 ± 3 617 μV/s, VM; 9 126 ± 3 098 vs.
8 482 ± 3 142 μV/s, P > 0.05).
The range in the muscle thickness means the range of 7 measurement sites
*
20
10
0
40
Proximal
Middle
Vastus intermedius
*
Distal
*
30
20
10
0
Proximal
Middle
60
40
20
Vastus lateralis
Vastus medialis
40
Rectus femoris
30
20
10
0
40
80
Distal
80
0
Muscle thickness
(mm)
30
Muscle thickness
(mm)
40
LN
Rectus femoris
Muscle thickness
(mm)
Muscle thickness
(mm)
Muscle thickness
(mm)
Muscle thickness
(mm)
LST
Proximal
Middle
Distal
Vastus intermedius
30
20
10
0
Proximal
Middle
Distal
60
40
20
0
Usui S et al. Low-load Slow Movement Squat … Int J Sports Med
Vastus lateralis
Vastus medialis
Fig. 2 Changes in the muscle thickness of the
quadriceps femoris; the rectus femoris (top
row) and the vastus intermedius (middle row)
measured at 30 % (proximal), 50 % (middle) and
70 % (distal) of the femur, and the vastus lateralis
and the vastus medialis (bottom row) before
(open bar) and after (closed bar) the LST (left)
and the LN (right) training. Values are mean ± SD.
An asterisk (*) indicates a significant (P < 0.05)
difference from the pre-test.
Downloaded by: University of Pittsburgh. Copyrighted material.
groups. The LST group showed significant gains in the muscle
thickness at 70 % of the RF ( + 10 %, P = 0.026) and at 50 % ( + 6 %,
P = 0.01) and at 70 % ( + 9 %, P = 0.002) of the VI after the training
▶ Fig. 2, left). No changes were observed in the LN group at all
(●
▶ Fig. 2, right).
sites (●
Statistical analysis
IJSM/4990/9.10.2015/MPS
Training & Testing
a
*
500
200
300
200
100
Hip extension
1 200
800
400
Lifting power
500
300
200
100
Hip extension
Knee extension
1 600
1 200
800
400
0
Squat jump
Counter-movement
jump
Fig. 4 Changes in the strength and power
variables in the LN group; maximal isometric hip
extension and knee extension torque a, 1-RM of
squat b, lifting power and leg extension power c
and squat and counter-movement jump height d
before (open bar) and after (closed bar) the training. Values are mean ± SD. An asterisk (*) indicates
a significant (P < 0.05) difference from the pre-test.
200
Lifting power
100
50
0
d
Height (cm)
Power (W)
c
20
150
1RM (kg)
Torque (Nm)
400
0
40
0
b
Squat
60
Leg extension
power
LN
a
50
0
d
1 600
0
100
Knee extension
Height (cm)
Power (W)
c
*
150
1RM (kg)
Torque (Nm)
400
0
Fig. 3 Changes in the strength and power
variables in the LST group; maximal isometric hip
extension and knee extension torque a, 1-RM of
squat b, lifting power and leg extension power c
and squat and counter-movement jump height d
before (open bar) and after (closed bar) the training. Values are mean ± SD. An asterisk (*) indicates
a significant (P < 0.05) difference from the pre-test.
b
Squat
60
40
20
0
Leg extension
power
Squat jump
Counter-movement
jump
Fig. 5 Relative changes in the strength and
power variables after the training in the LST group;
maximal isometric hip extension (HE) torque,
knee extension (KE) torque, squat 1-RM, lifting
power, leg extension power and squat (SJ) and
counter-movement jump (CMJ) height. Values are
mean ± SD. A hash mark (#) and a cross mark (†)
indicates a significant (P < 0.05) difference from
isometric hip extension torque and from squat
1-RM, respectively.
LST
Change from pre ( % )
40
30
20
#
#
10
0
Isometric
HE
torque
Isometric
KE
torque
Squat
1-RM
Lifting
power
#
LE
power
Leg extension power
Leg extension power did not significantly change in the LST
▶ Fig. 3c) and LN group (●
▶ Fig. 4c).
(●
Squat and counter-movement jump height
There were no significant changes in both squat and counter▶ Fig. 3d, 4d).
movement jump height in both groups (●
#
#
SJ
height
CMJ
height
Differences in the training-induced changes in the
variables
▶ Fig. 5 shows the relative changes in each variable from pre val●
ues for the LST group; those for the LN group are not shown
because no significant changes were observed in all the variables
▶ Fig. 4). The change of the isometric knee
in the LN group (●
extension torque was significantly lower than that of the isometric hip extension torque. Notably, the changes of the powerUsui S et al. Low-load Slow Movement Squat … Int J Sports Med
Downloaded by: University of Pittsburgh. Copyrighted material.
LST
related variables (i. e., lifting power, leg extension power, and
jump heights) were all lower than those of the strength variables
measured under the zero (isometric) or slow speed conditions
(i. e., isometric hip extension and 1-RM squat).
Discussion
▼
The main finding obtained here was that LST significantly
increased muscle size and strength, although the gains in muscle
thickness and strength depended on the measurement sites and
variables, respectively, but it did not produce significant changes
in all of the power-related variables. This supports our hypothesis, and suggests that LST can increase muscle size and taskrelated strength but has little effect on power production during
dynamic explosive movements.
In the LN group, there were no significant changes in all the variables. Tanimoto and Ishii [27] reported a similar result that
12-week knee extension training using LN did not increase isometric knee extension strength. It has been reported that training load at < 65 % 1-RM is less effective than high-load (65–85 %
1-RM) resistance training for increasing strength and size of the
muscles [9]. These findings together with the current result indicate that LN resistance training does not provide a sufficient
training stimulus for increasing muscle size and strength for
healthy young males. On the other hand, the LST group significantly increased muscle thickness, isometric hip extension
torque and 1-RM squat. The gain in 1-RM squat ( + 10 %) in this
study was the same as that ( + 10 %) observed in the seventh
week of the 13-week LST squat training conducted by Tanimoto
et al. [26]. As possible explanations for increasing muscle size
and strength by LST, Tanimoto and Ishii [27] suggested that the
tonic force generation pattern in LST causes increase in intramuscular pressure, restricting blood flow to the active muscles,
and it results in muscle deoxygenation and enhanced secretion
of growth hormone by intramuscular accumulation of metabolic
subproducts (e. g., lactate). Furthermore, Burd et al. [8] reported
that greater time under tension with the same load and repetitions (i. e., similar conditions used in this study; LST vs. LN)
increased the acute amplitude of mitochondrial and sarcoplasmic protein synthesis and also resulted in a robust stimulation of
myofibrillar protein synthesis after resistance exercise. Thus, it
is reasonable to assume that such factors as enhanced metabolic
stress and subsequent increases in myofibrillar protein synthesis
contributed to the gains in the muscle size and strength observed
in this study.
In the LST group, however, no changes were found in isometric
knee extension torque and the power-related variables, in spite
of the significant increases in muscle thickness, isometric hip
extension torque, and 1-RM squat. Also, muscle thickness
increased only in the RF (distal site) and VI (distal and middle
sites), and no changes were found in the VL and VM (discussed
later). These results indicate that the observed gains in muscle
strength and thickness in the LST group cannot be solely attributed to the enhanced metabolic stress and/or myofibrillar protein synthesis. As a well-documented fact, a training-induced
strength gain is most clearly observed in the task performed in
the training regimen, and this is called “task-specificity” [23].
For example, Sale et al. [24] reported that 19-week leg press
training significantly increased 1-RM leg press as well as muscle
size of the quadriceps femoris, but no change was found in maximal isometric knee extension strength, highlighting the imporUsui S et al. Low-load Slow Movement Squat … Int J Sports Med
IJSM/4990/9.10.2015/MPS
tance of neural factors (e. g., coordination among synergist
muscles) that contribute to the torque output (strength). In this
study, the subjects performed squat training only. Thus, it is possible that the training-induced strength gains were only
observed in 1-RM squat, which is the same exercise task performed in the training regimen, and hip extension, which is the
major action when (or a similar movement to) performing
squats. On the other hand, Tanimoto and Ishii [27] reported a
significant increase in isometric knee extension strength after
the LST training, but this is probably attributed to the fact that
the training was performed by knee extension in their study.
In addition, while the LST group increased muscle size and
strength, the power-related variables such as maximal lifting
▶ Fig. 3, 5). Conpower and leg extension power did not change (●
sidering the significant increase in isometric hip extension
strength, it is reasonable to assume that the power related-variables in the leg extensors (lifting and leg extension power and
jump performance) would increase as well. However, the current result contradicts this, indicating that LST can increase
muscle size and strength but has little effect on power production during dynamic explosive movements. As stated earlier,
Kanehisa and Miyashita [18] reported that resistance training
using slow speed had little effect on power production at a high
speed. Furthermore, Tanimoto et al. [26] reported that LST
changed muscular activity and force generation patterns during
dynamic movements to be more tonic, which may have unfavorable effects on dynamic power production. It has been suggested that instantaneous increase in muscle activation (i. e., less
tonic activation) is crucial for achieving high explosive power
[1]. To support this notion, some studies [2, 12] have reported
that a training-induced increase in the rate of force development, which is an index of the explosive power, was accompanied by an increase in RER. In this study, we found no significant
changes in maximal lifting power from the squatting position
and RER in the quadriceps femoris muscle during the task. This
suggests that LST induces neither unfavorable nor favorable
adaptations (i. e., decreased and increased RER, respectively),
and thus has little effect on dynamic power production. Behm
and Sale [7] described that the principle stimuli for the highvelocity-specific training response are the repeated attempts to
perform ballistic contractions and the high rate of force development of the ensuing contraction, regardless of muscle action
(isometric or concentric). Considering this, it is assumed that the
lack of improvement in the dynamic power-related variables in
the LST group would be attributed to the training modality
adopted (i. e., slow movement and tonic force generation).
The training intervention period set in this study was 8 weeks.
This is shorter compared to the previous studies that conduced
LST training for 12–13 weeks [26, 27]. As a result, we cannot rule
out the possibility that LST would increase explosive power to
some extent when the training period is extended longer than 8
weeks (e. g., 12–13 weeks). However, as mentioned, Tanimoto et
al. [26] reported that 13-week LST training changed muscular
activity and force generation patterns during dynamic movements to be tonic. Also, Tanimoto and Ishii [27] observed no
increases in single-joint isokinetic knee extension strength at
middle-high speed (90, 200, 300 deg/s) after 12-week LST training. On the other hand, several studies have found significant
increases in explosive power or strength at high speed after
short-term ( < 8 weeks) resistance training using ballistic movement and/or intention to move fast [11], indicating that changes
(improvements) in power-producing capacity often occur within
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Training & Testing
IJSM/4990/9.10.2015/MPS
Acknowledgements
▼
This study was not funded. The authors would like to thank all
the individuals who participated in this study.
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a relatively short-term. Considering these findings together, it is
reasonable to assume that LST training has little, if any, effect on
explosive power even when the training period is extended for a
long-term, for example 12 weeks or longer.
In the LST group, muscle thickness increased in the RF at 70 %
and in the VI at 50 and 70 % of the femur, but not in the other
sites. It has been reported that muscle hypertrophy occurs inhomogeneously among and along quadriceps femoris muscle after
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other 3 muscles composing the quadriceps femoris muscle.
Thus, it is possible that the RF was activated higher than the
other 3 muscles in the descending phase of the squat as well,
providing higher training stimulus to the RF. Additionally, it has
been reported that muscle activation level of the VI is higher
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VI has been shown to be higher than the other 3 muscles during
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these findings together with the fact that we used 50 % (submaximal) 1-RM load and parallel squat (knee-flexed position), muscle activation level (training stimulus) might have been higher in
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be a possible explanation for the observed inhomogeneous muscle hypertrophy. Further research is needed to clarify this.
In conclusion, the 8-week squat training program using LST
increased muscle size and task-related strength of the leg muscles. However, the LST did not increase any of the power-related
variables, and no changes were found in RER, which has been
reported to increase after high-load or power training and contribute to improved power production. These results supported
our hypothesis, and suggest that although LST can increase muscle size and task-related strength, it has little effect on power
production during dynamic explosive movements.
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Training & Testing
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Usui S et al. Low-load Slow Movement Squat … Int J Sports Med