Journal of Physical Activity and Health, 2012, 9, 1030-1035
© 2012 Human Kinetics, Inc.
Assessment of the Benefit of Powered Exercises
for Muscular Endurance and Functional Capacity
in Elderly Participants
Bert H. Jacobson, Doug Smith, Jeanette Fronterhouse, Crishel Kline, and Ali Boolani
Background: Aging is accompanied by a significant loss of strength which further contributes to loss of functional ability and a propensity for injury. The purpose of this study was to assess the effectiveness of power
assisted exercises on muscle endurance and functional capacity of elderly participants following 12 weeks of
supervised training. Methods: Elderly subjects (N = 53) were randomly assigned to either the experimental or
the control group. The experimental group trained for 12 weeks using powered exercise machines incorporating only concentric contractions while attempting to accelerate the preset, moving levers. Training involved 6
separate machines and using both upper- and lower-body musculature. Pre- and posttests consisted of Timed
Chair Stand, Up and Go Test, arm curl, bench press, leg extension, triceps extension, and the Berg Balance
Scale Assessment. Results: Analysis yielded significant improvements (P < .05) by the experimental group
over the control group in all measures of muscle endurance, balance, and functional capacity. An improvement
in balance paralleled muscle endurance improvements. Conclusions: Powered exercise equipment when used
actively, will generate both upper- and lower-body muscle endurance in elderly participants in a safe exercise
environment and such improvement also generated improvement in balance.
Keywords: balance, muscle
Between 2010 and 2030 the “Baby Boom” generation will reach age 65. This age explosion poses a variety
of challenges. One of the critical challenges with the shift
in demographics is in maintaining the quality of life.
Experts suggest that physical activity retards many agerelated changes, reduces the onset of many diseases and
increases longevity.1 A prominent age-associated malady
is the 40%–50% loss of muscle strength (sarcopenia)
which can be specific to age-associated muscle changes
as well as a sedentary lifestyle.2
Resistance training is not only an effective means
of retarding the normal, age-related loss of muscle mass
and strength,3,4 but also a means by which older persons
can significantly improve voluntary muscle strength.5,6
Indeed, muscle tissue responds to resistance training with
improved strength into the ninth decade, and improved
strength is related to improved balance and a reduced risk
of falling.7 However, the choice of equipment may be of
importance, particularly for the elderly. For instance, free
weights and weight machines are equally effective in producing strength gains,8 but they both require concentric
and eccentric contractions, the latter resulting in significantly greater muscular soreness9–12 which is magnified
in older individuals, making for slower recovery.13,14
The authors are with the Dept of Health and Human Performance, Oklahoma State University, Stillwater, OK.
1030
Thus, acute muscle soreness may not promote exercise
adherence and may even be a deterrent to exercise. Weight
machines are considered safer because the machines
guide the path of resistance, while free weights require
balance and control,15 which can contribute to injuries.16
An alternative to isotonic exercises is isokinetic
resistance exercise. Isokinetic exercises are safe17 and
effective for developing muscle strength18 by using specialized machines that only require concentric muscle
contractions at constant limb speeds. A relatively new
innovation is exercises performed on powered equipment. Powered equipment are fitted with motors and
gearboxes that move the handles or foot pedals through
predetermined speeds and range of motion. In contrast
to other exercises, the participant does not attempt to
overcome resistance, but rather applies force with
(assists) the movement of the machine, as if trying to
push or pull levers/pedals in an attempt move them
faster in the direction that they are already moving.
Like isokinetic exercises, powered exercise equipment
only requires concentric contractions and joint movement
speed is controlled by the machine. No previous studies
have sought to determine the efficacy of maintaining or
increasing muscle endurance by exercising with this type
of equipment. The purpose of this study was to assess
the effectiveness of power assisted exercises on muscle
endurance and functional capacity of elderly participants
following 12 weeks of supervised training.
Assessment of the Benefit of Powered Exercises 1031
Methods
Subjects
Subjects were 53 male (n = 15) and female (n = 38)
volunteers living in independent living facilities in a Midwestern city. Characteristics of the subjects are illustrated
in Table 1. Subjects were contacted by the researchers
and were briefed on the requirements and objectives
of the study. Volunteers were asked to complete an
informed consent document approved by the University
Institutional Review Board (IRB), an initial screening
questionnaire (Par-Q & You), an Exercise Readiness
Questionnaire, and a health screening questionnaire. After
determination of eligibility, the subjects were randomly
assigned to the exercise or control group.
Procedures
Pre- and posttest measures were collected on the
30-Second Chair Stand Test,19 the Timed 8-ft Up and
Go Test, a seated 30 sec arm curl, a seated bench press,
leg extension, triceps extension, and a modified Berg
Balance Scale Assessment. The 30-Second Chair Stand
Test is a valid measure20 of lower-body strength of older
Table 1 Subjects Characteristics by Gender
Variable
Mean
SD
Experimental group
Male age (yrs)
Female age (yrs)
79.9
79.5
5.1
6.0
Control group
Male age (yrs)
Female age (yrs)
76.2
81.3
4.5
5.2
Experimental group
Male age (kg)
Female age (kg)
82.1
75.3
5.1
6.2
Control group
Male age (kg)
Female age (kg)
85.
73.5
6.0
5.8
Experimental group
Male age (cm)
Female age (cm)
177.1
168.7
5.3
4.4
Control group
Male age (cm)
Female age (cm)
179.4
167.9
6.2
5.1
Experimental group
Male age (BMI)
Female age (BMI)
28.4
29.1
4.8
4.4
Control group
Male age (BMI)
Female age (BMI)
28.8
27.8
3.8
4.2
adults and is an effective method of determining agerelated declines, in discriminating between fallers and
nonfallers,21 and in assessing the effects of exercise in
the elderly.22 Correlations between chair stand scores and
leg press scores are reported to be r = .78 for men and r
= .71 for women.20
The Timed 8-ft Up and Go Test is a measure of agility and dynamic balance and discriminates between high
and low-active elderly and response to changes resulting
from different levels of physical activity. Performance on
the 8-ft Up and Go Test is related to the Berg Balance
Scale (r = .71), walking speed (r = .61), and the Barthel
Index of ADLs (r = .78).23 The Seated 30-Second Arm
Curl (males—8 lbs.; females—5 lbs.) is a measure of
upper-body strength developed expressly for older adults,
and correlated to a combined measure that included
1-RM biceps curl for both men (r = .84) and women (r
= .79).17 The test is also accurate in determining agerelated declines in strength and it discriminates levels of
physical activity.24
Bench Press muscle endurance assessments followed
recommendations and norms established by Golding.25
Participants completed full repetitions to a cadence of 30
rep/sec with weights of 80 lbs. and 35 lbs. for men and
women respectively. In addition, based on Golding’s25
norms, Leg Extension assessments were measured in
repetitions of 50% BWT by both men and women using
an isotonic weight machine. Triceps Extensions were
done with an overhead pulley connected to a weight stack
with a load representing 33% BWT weight for both males
and females. The Berg Balance Scale is a valid measure
of balance and stability in older adults26,27 containing 14
balance activities which results in a combined score used
for analysis and comparison.27
For training, participants were transferred by staff
members from their living centers to the training facility 2×/wk over a 12-week period with sessions lasting
approximately 30 minutes. Training involved 6 separate
machines (Shapemaster) designed for selective joint
function specific to muscles in the legs, torso, upper
body, and arms. Each machine provided multifunction
movements by incorporating both agonist and antagonist muscles. For instance, the seated bench press/row
machine was designed to strengthen both the chest
(pectoralis major) and upper back (latissimus dorsi) area
along with associated muscles (ie, biceps and triceps).
In addition, the machines included foot pedals designed
to strengthen the knee and hip extensors simultaneously
to upper-body work. Three machines were designed to
strengthen the major upper- and lower-body muscles and
3 machines were designed to strengthen the trunk muscles
by involving trunk rotation, trunk flexion/extension, and
trunk lateral flexion. For each machine, the participants
exercised for 5 minutes with speeds between 14 and 16
repetitions per minute for an average of 450 repetitions
per session. Participants were supervised and proper
safety standards and technique were constantly monitored
and were encouraged to exert effort. Data were omitted
from analysis for anyone missing over 25% of the exercise
1032 Jacobson et al
sessions. The control group was pre- and posttested at the
same time as the experimental group and was asked to
maintain their usual activity and lifestyle for the duration
of the study. Activity that they were already involved in
such as seated rhythmic exercises were allowed, but they
were asked not to initiate new activities for the duration
of the study.
Data Analysis
Pre- and postdata were collected and analyses of variance
(ANOVA) with repeated measures were used to compare
pre- and postmeans of each dependent variable (2 time
× 2 group). Newman-Keuls post hoc analyses were used
to determine the site of significant mean differences. An
alpha level of < .05 was used to determine significance.
Results
Of an original pool of 63 eligible subjects, 11were lost
to follow-up due to a) relocation to another facility (n =
2), b) failure to attend the minimum number of sessions
(n = 3) and, c) recurring health issues (n = 6). Means,
standard deviations, and confidence intervals were calculated and analyses of variance (ANOVA) with repeated
measures were conducted on each selected measured
variable (Table 2). Analysis yielded significant between
group improvements by the experimental group over the
control group in the 30-Second Chair Stand (F = 13.86,
P = .006) and the Timed 8-ft Up and Go (F = 6.68, P =
.013) test. Significant improvements by the experimental
group were also found for the seated 30 Second Arm
Curl (F = 16.39, P = .001), the Bench Press (F = 19.43,
P < .001), the Leg Extension (F = 36.73, P < .001), the
Triceps Extension (F = 32.60, P < .001), and in Balance
(F = 40.64, P < .001) when compared with the control
group. The experimental group demonstrated significant
within-group improvements for all pre- and posttest
dependent variables, while the control group failed to
demonstrate any significant changes.
In separating the groups by gender, results suggested
that both males and females benefitted equally from the
exercises with the exception of the Up and Go and the
Bench Press. Both males and females in the experimental
group improved significantly (P < .05) over the control
group in the Chair Stand, Arm Curl, Leg Extension,
Triceps Extension, and in Balance. For males, the experimental and control groups did not differ significantly in
the Up and Go assessment. While no significance was
obtained, the experimental group improved 41.3% in the
Up and Go compared with a loss of 0.8% by the control
group. A substantial statistical variance in performance
dictated the lack of significance in this variable.
Discussion
Age-related loss of muscular strength and endurance
can be reversed and significantly improved with proper
resistance exercise.30 In the current study the proportional
improvements posted by the treatment group in the area
of muscle endurance after 12 weeks were Chair stand
(33.0%), Arm curl (27.9%), Bench press (50.1%), Leg
extension (34.6%), and Triceps extension (24.1%).
Although muscular endurance and strength are separate
fitness components, they are closely related and increases
in muscle endurance achieved with progressive submaximal repetitions will subsequently increase muscle
strength.31 Predictably, those exercises that were similar
to the assessments (ie, bench press, leg extensions)
produced significant posttest improvement in isotonic
muscle endurance tests. It also warrants mentioning that
while the training required only concentric contractions,
these results were obtained for isotonic (concentric and
eccentric contraction) exercise. In exit interviews, no
one reported uncomfortable muscle soreness and no
participant dropped out of the study due to injury or
acute soreness. Those that dropped out of the study did
so for reasons not under their control (ie, medical issues,
relocation, etc). Furthermore, the exercise protocol was
identified as nonthreatening by the participants, which
may have contributed to the adherence and compliance to
the exercise protocol. Indeed, it has been suggested that
increased confidence in the safety of the activity helps
participants overcome barriers to exercise.32
Perhaps most surprisingly, the increases in muscle
endurance were associated with significant increases in
mobility and balance as assessed by the Berg Balance
Scale. For instance, the timed 8ft-Up and Go results
improved by 27.9% for the experimental group and by
only 1% for the control group, and the experimental
group improved by approximately 33% in the Berg Balance Scale test while the control group lost slightly more
than 1% (Table 2). This is notable since the exercises
performed in the current study were seated exercises,
however; these results are in agreement with others who
concluded that exercise can improve fall-related gait
kinematics and that lower limb strength training programs
should be recommended to the elderly to reduce the risk
of falling.33,34 To further substantiate such claims, we correlated pretest Berg Balanced Scale scores with balance
and the Timed 8-ft Up and Go test, the Chair Stand, and
Leg Extensions and found moderately strong correlations
(r = .059–0.72).
A limitation of equipment is that the participant
does not have to exert any effort and the levers/pedals
will still move. While passive movement is beneficial in
rehabilitation circumstances where range of movement
is being reestablished, such activity will not generate an
increase in muscle tissue; results will only be realized if
the participant actually applies force with the movement.
However, it was observed that once the participants felt
confident in the exercise protocol and in the machines,
they increased their effort.
In conclusion, these results suggest that powered
exercise equipment when used actively, will generate
both upper- and lower-body muscle endurance in elderly
participants in a safe exercise environment. In addition, balance and functional ability can improve with
1033
9.89
11.21
12.79
13.85
15.86
21.28
Experimental triceps extension
Control triceps extension
Experimental balance
Control balance
8.50
Control bench press
Experimental leg extension
7.36
Experimental bench press
Control leg extension
12.48
Control arm curl
2.28
12.18
10.23
Control 8-ft up & go
Experimental arm curl
1.07
13.52
Experimental 8-ft up & go
1.28
0.77
0.89
0.53
1.68
0.68
1.09
0.64
1.32
0.82
0.81
9.43
Control chair stand
SD
0.49
8.19
Experimental chair stand
Pre-mean
18.71–23.85
14.30–17.42
12.07–15.64
11.72–13.86
8.86–13.56
8.52–11.27
6.29–10.70
6.07–8.66
9.77–15.08
8.68–11.98
7.57–16.78
11.35–15.69
7.80–11.05
7.1–9.76
95% CI
21.00
21.05
12.29
15.87
9.21
13.31
6.78
11.05
10.42
13.08
12.28
10.57
9.28
10.89
Post-mean
–1.3%
+33%
–11.3%
+24.1%
–17.8%
+34.6%
–20.2%
50.1%
–16.5%
+27.9%
–0.8%
+21.8%
–1.6%
+33.0%
Gain
0.88
0.54
1.56
0.69
1.24
0.71
1.23
0.74
1.13
0.71
1.60
0.75
0.76
0.86
SD
19.19–22.80
19.96–22.15
9.96–14.60
14.48–17.26
6.71–11.72
11.87–14.75
4.31–9.26
9.55–12.55
8.36–12.92
11.66–14.50
9.05–15.51
9.05–12.09
7.76–10.80
9.93–11.79
95% CI
Table 2 Pre- and Posttests Means, Standard Deviation (SD), Confidence Intervals (CI), and Gain by Group
F
40.64
32.60
36.73
19.43
16.39
6.68
13.86
P
<0.000
<0.000
<0.000
0.001
0.001
0.013
0.006
1034 Jacobson et al
exercises that do not incorporate balancing or orthostatic
hypotension, both which may pose a risk if included in
an exercising exercise protocol. It is axiomatic that the
quality of life deteriorates with incidents or risk of falling.35 Improvement in balance and stability as evident by
a muscle endurance training program should logically
equate to a reduction in falls, thereby contributing to
greater quality of life.
Acknowledgments
This work was supported by the Shapemaster, Inc. (Grant
number: ED-08-RS-100).
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