Die Effekte eines Power Plate-Trainings gegenüber einem

Die Effekte eines Power Plate-Trainings gegenüber einem Fitnesstraining auf
die Muskelfitness und Muskelmasse bei untrainierten Personen.
Y. Osawa et al. Scand J Med Sci Sports, 2011: 1-12
Ziel der Studie:
Untersuchung ob ein Power Plate-Training oder ein allgemeines konventionelles Krafttraining einen
positiven Einfluss auf die Muskelfitness und den Muskelaufbau bei gesunden untrainierten Personen hat.
Methoden:
Diese 13- wöchige Studie wurde mit 32 gesunden untrainierten Probanden (Alter 22-49 Jahre) durchgeführt
(85% der Teilnehmer waren Frauen). Die Teilnehmer wurden gleichmäßig in 2 Gruppen aufgeteilt: (1)
Power Plate-Gruppe (35 Hz, low Amplitude); (2) Konventionelles Krafttraining (ohne Vibration). Alle
Teilnehmer trainierten je 2-mal pro Woche über einen Zeitraum von 13 Wochen. Es wurden folgende
Komponenten untersucht: Muskelzuwachs (MRI), Muskelkraft, Sprungkraft (Counter-Movement-Jump) und
Kraftausdauer.
Ergebnisse
Das Power Plate-Training resultierte in einem stärkeren Muskelzuwachs als das konventionelle Training.
Nur die Power Plate-Gruppe könnte einen Muskelzuwachs im Rückenstrecker erzielen. Die Power PlateGruppe zeigte eine größere Zunahme der Muskelkraftparameter (+63.5% und +76.7%) im Vergleich zu
dem konventionellen Training (+25.6% und +17.8%). Auch die Sprungkraft war nach dem Power PlateTraining (+15.0%) im Vergleich zum konventionellen Training (+11.3%) deutlich verbessert. Beide
Trainingsgruppen zeigten weiterhin eine Verbesserung der Rumpfmuskulatur.
Fazit:
Diese wissenschaftliche Studie beweist, dass ein 13-wöchiges Power Plate-Training bei untrainierten
Personen in einem Muskelzuwachs und einer deutlichen Verbesserung verschiedener
Muskelkraftparameter resultiert. Ein Muskelzuwachs im Rückenstrecker könnte nur nach dem Power
Plate-Training, nicht aber nach dem konventionellen Krafttraining beobachtet werden. Die beobachteten
Kraftverbesserungen der Rumpfmuskulatur und die höhere Muskelmasse im Rückenstrecker deuten
darauf hin, dass ein Power Plate-Training förderlich in der Prävention und Rehabilitation von
chronischen Rückenschmerzen förderlich sein kann.
© Power Plate
Abstract Muskelfitness V 1.0, Stand 01.08.2012
Seite 1 von 1
Scand J Med Sci Sports 2011
doi: 10.1111/j.1600-0838.2011.01352.x
& 2011 John Wiley & Sons A/S
Effects of resistance training with whole-body vibration on muscle
fitness in untrained adults
Y. Osawa1, Y. Oguma1,2
1
Graduate School of Health Management, 2Sports Medicine Research Center, Keio University, Kanagawa, Japan
Corresponding author: Y. Osawa, 4-1-1, Hiyoshi, Kohoku-ward, Yokohama City, Kanagawa, Japan. Tel: 181-45-566-1090,
Fax: 181-45-566-1067, E-mail: [email protected]
Accepted for publication 17 May 2011
The effects of resistance training (RT) combined with wholebody vibration (WBV) on muscle fitness, particularly muscle
hypertrophy and neuromuscular performance, are not well
understood. We investigated the effects of WBV in healthy,
untrained participants after a 13-week RT course by
performing magnetic resonance imaging and by measuring
maximal isometric (with electromyography) and isokinetic
knee extension strengths, isometric lumbar extension torque, countermovement-jump, knee extension endurance,
and sit-ups. Thirty-two individuals (22–49 years old) were
randomly assigned to RT groups with (RT-WBV, n 5 16) or
without WBV (RT, n 5 16). Following the RT course,
significantly higher increases in the cross-sectional areas
of m. psoas major (vs baseline values) and erector spinae
muscle (vs the RT group) were observed in the RT-WBV
group (110.7%, Po0.05; 18.7%, Po0.05) compared with
the RT group (13.8%, P 5 0.045; 0.0%). Higher increases
from baseline were also observed in maximal isometric
force, concentric knee extension torque, countermovement-jump, and maximal isometric lumbar extension torque
in RT-WBV (163.5%; 176.7%, 115.0%, and 151.5%,
respectively; Po0.05) than in those of RT (125.6%,
P 5 0.001; 117.8%, P 5 0.18; 111.3%, P 5 0.001; and
126.4%, Po0.001, respectively). The WBV-induced increases in muscle hypertrophy and isometric lumbar extension torque suggest a potential benefit of incorporating
WBV into slow-velocity RT programs involving exercises
of long duration.
Recently, resistance training (RT) combined with
whole-body vibration (WBV) has become popular
among untrained middle-aged people. Although it
has been suggested that RT with WBV enhances
muscle strength, particularly in untrained adults
(Marin & Rhea, 2010), the efficacy of WBV when
incorporated into RT programs for improving muscle mass, strength, power, and endurance compared
with the identical training without WBV is less clear.
Among six recent studies, only Delecluse et al. (2003)
found that WBV led to significant additional increases in muscle strength and power, as the other
studies did not detect any additional effects resulting
from the addition of WBV to RT programs (de
Ruiter et al., 2003; Ronnestad, 2004; Kvorning
et al., 2006; Carson et al., 2010; von Stengel et al.,
2010). However, two studies reported that exercise
combined with WBV significantly increased the
cross-sectional area (CSA) of thigh muscles in older
individuals (460 years of age) (Bogaerts et al., 2007;
Machado et al., 2010). Although these represent the
only findings to suggest that WBV training stimulates morphological changes in muscles, an identical
exercise group in the absence of WBV was not
included in the evaluations. Therefore, further exam-
ination of the effects of WBV training on muscle
hypertrophy is needed.
To date, a standard WBV training program has
not been established. The degree of muscle stimulation during WBV exercise is dictated by the
amount of force generated by the vibration platform
(actuator) that is transferred to the human body
(resonator) (Rittweger, 2010). It was demonstrated
previously that the acceleration of vibration platforms increases under weight-loaded conditions (Pel
et al., 2009; Osawa et al., 2011b). If the actuator
produces a larger force, the degree of response in the
resonator would be expected to correspondingly
increase. However, as a few studies did not detect
any additional muscle strength or power gains with
heavy-loading RT regimens combined with WBV
[e.g., eight repetitions of 8–10 repetition maximum
(RM) or 10 repetitions of 75–90% 1 RM], conventional RT regimens do not appear suitable for WBV
training programs (Ronnestad, 2004; Kvorning et al.,
2006; Carson et al., 2010). Therefore, longer exposure to vibration during muscle contractions may be
necessary to elicit WBV per se effects on neuromuscular systems. This speculation is supported by a
study of Bongiovanni et al. (1990), who found that
1
Osawa & Oguma
reductions of electromyographic activity, motor unit
firing rates, and contraction force were observed
after 30-s muscle contractions with locally applied
vibration. This may have been due to vibrationinduced pre-synaptic inhibition and/or transmitter
depletion in Ia excitatory pathways. In consideration
of these reports, we anticipated that an intentional
slow-velocity RT program that increases the time
muscles are under tension would be suitable to
combine with WBV. In addition, slow-velocity RT
also involves less momentum, resulting in a more
evenly applied muscle force throughout the range of
motion and is amenable to the addition of lighter
external loads than conventional training regimens,
even when progressive overloading is needed to
overcome strength-gain plateaus (Westcott et al.,
2001; Tanimoto & Ishii, 2006). Here, we hypothesized that slow-velocity RT combined with WBV
would lead to increases in muscle mass, strength,
power, endurance, and neuromuscular activities.
The aim of this study was to investigate the effects
of 13-week RT combined with WBV on muscle
hypertrophy, strength, power, neuromuscular activity, and local muscle endurance compared with the
identical training lacking WBV in untrained, healthy
adults. Participants in both training groups were
subjected to several performance tests, in addition
to measuring the CSA of abdominal muscles, to
assess the effects of WBV on the basis of changes in
the pre-training and post-training measurements.
University and written informed consent was obtained from
all participants.
Randomization procedure
Participants were randomly assigned to either an RT with
WBV (RT-WBV, n 5 17) group or a non-WBV RT (RT,
n 5 16) group (Fig. 1). A restricted randomization (blocking
and stratification) was used to allocate participants into one of
the two groups. First, six matrices (age, 20s, 30s, or 40s;
gender, female or male) were created to stratify the participants. Second, we prepared six envelopes for each stratified
group, with each envelope containing 10 cards labeled with
either ‘‘RT’’ or ‘‘RT-WBV’’ (RT-WBV:RT, 5:5). Finally, after
the completion of all of the pre-training tests, each participant
drew a card from the envelope corresponding to their stratified
group, and was allocated to either training group as designated by the selected card.
Training programs
Vibration conditions
To deliver WBV to the RT-WBV
group, a synchronous
s
vibration device (Power Plate Next Generation, Power Plate
International, Northbrook, Illinois, USA) equipped with the
platform pad provided by the manufacturer was used. We
applied WBV at a frequency and amplitude of 35 Hz and
2 mm, respectively, throughout the trial because nearly all
participants in a pilot study experienced discomfort in their
head and chest regions when exercises were performed in
supine and prone positions at higher frequencies or amplitudes,
or without the platform pad. Mean acceleration magnitudes of
the vibration platform device with and without weight loading
were reported in a previous study (Osawa et al., 2011b).
RT program
Materials and methods
Subjects
Figure 1 shows the flow of the study. Thirty-three untrained
adults [6 males (M) and 27 females (F), 22–49 years old]
volunteered for this study. Participants were recruited from
local residents (n 5 26) and from graduate school students of
Keio University (n 5 7) using posted advertisements. Power
analysis was performed with the power set at 0.80 and an alevel of 0.05 under the hypothesis that RT with WBV would
increase the CSA of m. psoas major as the primary outcome.
The analysis setting with balanced data (equal number of
participants in each group), and an expected effect size and
standard deviation (SD) of 0.2% and 0.19%, respectively,
revealed that a sample size of 14 participants in each test group
was required for the detection of WBV effects. The eligibility
criteria for participants were 20–49 years old, no experience
with RT for at least 6 months before the study, could refrain
from engaging in any regular vigorous activities, strength
training, or stabilization training, and could maintain routine
daily life throughout the trial. The health and medical history,
current medical conditions, and signs and risk factors of
cardiovascular or orthopedic diseases of each potential participant were evaluated using a self-administered Physical
Activity Readiness Questionnaire (PARQ; Thomas et al.,
1992). If an individual answered ‘‘No’’ to all questions, he
or she was considered a suitable candidate and was entered
into the study. The exclusion criteria were pregnancy, history
of severe orthopedic abnormality, diabetes, or acute hernia.
This study was approved by the local ethics committee of Keio
2
After performing a standardized warm-up involving operating
an ergometer for 5 min followed by stretching (e.g., modified
hurdler’s stretch), participants, who wore socks, but no shoes,
performed two exercises for lower extremities with their hands
free (half squat, knee angle, 201–901 (full extension 5 01), hip
angle, 201–301, to 901 (full extension 5 01); Bulgarian squat,
knee angle, 201–901; hip angle, 201–301 to 901) and six
exercises for trunk muscles (roll back, trunk curl, hip walking,
leg raise, back extension, and stabilization exercise) on the
vibration platform either with (RT-WBV group) or without
WBV (RT group) (Table 1). The position adopted in each
exercise, including photographs, has been reported previously
(Osawa & Oguma, 2011a). Although there is no well-established movement cadence for achieving optimal muscle fitness
gains, here, we configured the training program to consist of a
cadence of 4 s concentric phase (lifting), 2 s no-relaxing phase
(isometric phase), and 4 s eccentric phase (lowering) to minimize momentum and to achieve a more evenly applied muscle
force throughout the range of motion (Smith & Bruce-Low,
2004). Each exercise was performed for eight repetitions with
the cadence with intermittent rest periods of 60 s between sets,
with the exception of the roll back and hip walking exercises,
which were performed continuously for 64 and 48 s, respectively, without any isometric phase. All cadences were strictly
controlled using a metronome (SQ-77, Seiko, Tokyo, Japan).
Weight loading was based on individual bodys mass (Table 1).
As the g force produced by the Power Plate increased with
weight loading on the platform, the g force experienced by
participants in the RT-WBV group and/or weight loading
Vibration training effects on muscle fitness
Fig. 1. The flow of participants through the trial. Participants were randomly assigned to one of the two training groups and
performed twice-weekly training (60-min sessions) either with (RT-WBV) or without (RT) WBV (frequency, 35 Hz; amplitude,
2 mm) for a 13-week training period. All participants were subjected to tests and assessments before, during (after a 7-week
training period), and following training (after a 13-week training period) to evaluate muscle hypertrophy, muscle performance
(muscle strength, power, endurance), physical activity, and nutritional assessments, with the exception of MRI tests and
physical activity assessment, which were only performed before and after the training period. FFQg, food frequency
questionnaire based on food groups, MRI, magnetic resonance imaging, RT, resistance training; RT-WBV, RT with wholebody vibration.
Table 1. Exercise protocol used in the present study
Period
(week)
Pre-tests
1
2–4
5–7
Mid-tests
8–13
Volume (set/
exercise)
Weight-loading conditions
Leg exercises
Trunk exercises
Squat (two legs)
Bulgarian squat
(one leg)
Roll back exercise
Trunk curl
Back extension
Hip walking
Leg raise
Stabilization
1
2
2
Body weight
Body weight
Body
weight
2
Progressively increased every 2 weeks and reached 30% and
45% of body mass in women and men, respectively
10% and 15% body mass for women and for men, respectively
Progressively increased
using 1–3.4
and 1–5. 6 kg dumbbells
in women and
men, respectively
Post-tests
A weight jacket (Kool Katz, Pokal Industries Pvt Ltd., Sialkot, Pakistan), in which 1–20 kg of weight bars could be added around the abdominal and lower
back area, and dumb bells were used for additional weight loading for the two leg exercises. Dumb bells were used for three of the trunk exercises.
intensity within the two groups would have varied if training
intensity was decided by the maximum strength test. Therefore,
we configured the weight loading based on the performance of
a few individuals (e.g., not overly challenging and the degree of
muscle soreness the day after training session) in pilot trials. s
As the laboratory was equipped with two Power Plate
machines, training sessions were conducted with a maximum
of two participants, who were strictly and closely supervised
by the investigators. After each training session, participants
ingested a multi-vitamin supplement (Nature Made, Otsuka,
Tokyo, Japan) to provide the minimum reference dietary
intakes recommended by the Japanese Ministry of Health
and to minimize the effects of confounding related to insufficient food intake, particularly vitamins.
3
Osawa & Oguma
Magnetic resonance imaging (MRI)
MRI was performed using a 1.5 T imager (Intera 1.5t, Phillips
Medical Systems, Best, the Netherlands). As it has been
suggested that soft tissues, joints, or items such as shoes and
pads dampen the vibration magnitude (Rittweger, 2010), we
anticipated that exercises performed in prone and supine
postures would maximize the vibration efficacy on trunk
muscles, which would be in direct or close contact with the
platform, when compared with the effects of standing exercises
on thigh and leg muscles. Thus, we decided to configure the RT
exercise program to target mainly trunk muscles and investigated the additional WBV effects on muscle hypertrophy using
MRI only in trunk muscles due to budget restraints. The CSA
of m. psoas major, m. rectus abdominis, m. anterolateral
abdominal (IABD; obliquus internus abdominis1obliquus externus abdominis1transversus abdominis), multifidus, erector
spinae muscle, and quadratus lumborum muscle were determined from lumbar axial MRI images, which were obtained
parallel to the L4–L5 disc space level. A single 10 mm axial slice
was obtained using a T1-weighted image. The other MRI
parameters were as follows: TR, 450 ms; TE, 20 ms; FA, 901;
NA, 1; matrix, 256 256; FOV, 400 400 mm; pixel size,
1.56; scan time, 11.3 s (SENSE mode); and TSE factor, 6. A
body coil was used to image abdominal sections (SENSE-Body
Coil, Phillips Medical Systems). The DICOM images obtained
were analyzed with ZedView 3.1 software (Lexi, Tokyo, Japan).
Segmenting the CSA of muscle was based on the brightness of
the MR value, and if a part of the CSA delineation was unclear,
a free hand area calculation was performed (Arai et al., 2004).
The average of the CSA of each left and right muscle was used
for further statistical analysis.
All MRI measurements were performed by a radiologist
(M.R.I.) and a medical software programmer (CSA measurements), who had no knowledge of the study design (e.g.,
purpose of the present study, participants’ information, and
grouping), except that the CSA measurements were supplementarily performed by an investigator for five women’s data
and all the CSA of multifidus, erector spinae muscle, and
quadratus lumborum muscle with free hand area calculation
using the DICOM viewer software OsiriX ver. 3.9 (http://
www.osirix-viewer.com). Intraclass correlation coefficient
(ICC) tests were also evaluated within one week of all of
measurements for four participants and one investigator;
r 5 0.99 (m. psoas major), r 5 0.98 (m. rectus abdominis),
r 5 0.91 (IABD), r 5 0.94 (multifidus), r 5 0.97 (erector spinae
muscle), and r 5 0.96 (quadratus lumborum muscle).
Performance tests
After the standardized warm-up described in the RT program
section, the following performance tests (listed in the order
they were conducted) were evaluated before (Pre), after 7
weeks of training (Mid), and after the completion of the 13week training period (Post). Participants performed light
stretches between tests.
Countermovement-jump test for muscle power
As the recruitment of participants was divided into two
periods, and the instrument used for the muscle power test
was only available during the second recruitment period, only
23 participants (RT-WBV, M: 1, F: 11; RT, M: 1, F: 10;
38.6 8.2 years old) performed
countermovement-jumps
s
while wearing a Myotest accelerometer on the waist (Myotest, Royal
Oak, Michigan, USA) (Casartelli et al., 2010). The
s
Myotest automatically calculates jump height from the
obtained flight time (t) by estimating the height of the rise of
4
the body center of gravity (h) during countermovement-jump
(h 5 1/8gt2, where g 5 9.81 m/s2). In a standing position,
participants first made a downward movement by bending
their knees and hips, and then jumped as high as possible while
keeping their hands on their waist. After returning to a
standing position, the participants were permitted a short
intermittent rest of a few seconds between each jump. The
jump was repeated five times, and the mean value of countermovement-jump height (cm) was recorded. The test was
conducted twice, with an interval of 3 min, and the highest
mean jump height was used for further analyses. The ICC for
test–retest reliability of the countermovement-jump test was
r 5 0.96.
Maximal knee extension strength and endurance tests
Maximal voluntary isometric force and isokinetic knee extension torque, and local muscular endurance powersand work
were measured on the right side using a Kin-Com KC500H
device (Chatteex, Hixson, Tennessee, USA). During the tests,
the right upper leg, ankle, and the hips were stabilized with
safety belts. After gravity correction was performed in accordance with the manufacturer’s guidelines, participants were
seated with a hip joint angle of 801 and arms crossed in front
of the chest, and maximal isometric 5-s contractions were then
measured at a knee angle of 601. Maximal isokinetic concentric and eccentric knee extension torque was measured at
knee angles of 801–201 and a velocity of 601/s. The local
muscle endurance test, consisting of 30 consecutive concentric
knee extensions, was performed at knee angles of 801–201 and
a velocity of 601/s. Total work (J) and average power (W)
during local muscular endurance test were measured. The
measurements for all strength tests were repeated twice with 3min rest intervals, and the peak force or torque obtained,
which was normalized to body mass (N/kg, or N m/kg) for the
maximal voluntary isometric and isokinetic tests, respectively
were used for further analyses. The ICC for test–retest
reliability were r 5 0.97 (isometric contraction), r 5 0.86 (isokinetic concentric contraction), r 5 0.91 (isokinetic eccentric
contraction), and r 5 0.79 (local muscular endurance).
Surface electromyography (sEMG)
sEMG signals from the vastus medialis (VM) and vastus
lateralis (VL) muscles of the right leg were recorded using a
TeleMyo 2400 T V2 system (Noraxon Inc., Scottsdale, Arizona, USA) with disposable Ag/AgCl snap electrodes (EM272, Noraxon Inc.) during the Bulgarian squat exercise with or
without WBV and the isometric knee extension force test. The
figure eight-shaped adhesive area of the electrodes was
4 2.2 cm, the two circular conductive areas were 1 cm in
diameter, and the inter-electrode distance was 2 cm. After the
skin over the respective muscle belly was lightly abraded, the
electrodes were fixed in accordance with the Surface Electromyography for the Non-Invasive Assessment of Muscles
guidelines (Hermens et al., 1999). After the electrodes were
attached, the participants sat on a chair for at least 5 min to
acclimatize the skin with the electrodes. The sEMG signals
were sampled at 3000 Hz and subsequently band-pass filtered
(15–500 Hz).
The processing of sEMG data was performed using MyoResearch XP software, Master Package ver. 1.06.74 (Noraxon
Inc.). As suggested previously by Abercromby et al. (2007),
raw EMG signals obtained during exercise with WBV include
motion artifacts caused by the WBV source. Thus, we applied
band stop filter analyses at Nfv, where fv is the vibration
frequency, and the stop-band was equal to Nfv 0.5 Hz (i.e.,
0.5fv, 1fv, 2fv, . . ., 14fv). The raw EMG signals obtained from
Vibration training effects on muscle fitness
the isometric contraction test were converted to an average
root-mean square (EMGrms) with 0.5 s smoothing windows
to compare the RT-WBV and RT groups. The 0.5 s time
epochs around the isometric contraction
force peak, which
s
were identified using a Kin-Com KC500H device, were used
for further analyses.
Trunk muscle strength and endurance
We measured back extensor torque with an isometric lumbar
extension machine (MedX, Orlando, Florida, USA) using
testing positions that were standardized following the manufacturer’s guidelines. After the participant was seated in the
lumbar extension machine, the pelvis was stabilized, and while
the participant rested against the upper back pad (the angle of
full extension was 01), a counterweight was adjusted to
neutralize gravitational force on the head, torso, and upper
extremities. Maximal isometric lumbar extension torque was
then measured in the sitting position through a 721 arc of
lumbar motion (at 721, 601, 481, 361, 241, 121, and 01 of trunk
flexion). The ICC for test–retest reliability of each angle
ranged from r 5 0.83 to 0.94. The maximal isometric lumbar
extension torque at 601 of trunk flexion was used for further
analyses, because the position gave the highest reliability in
our laboratory (r 5 0.94) and in a previous report (r 5 0.96)
(Graves et al., 1990).
Abdominal muscle endurance was evaluated by the total
number of sit-ups performed in 30 s. We applied the sit-up test
used in the New Japan Fitness Test formulated by the
Japanese Ministry of Education, Culture, Sports, Science,
and Technology, which is nearly identical to that used in the
Eurofit Fitness Testing Battery, with the exception of arm
position. A detailed explanation of the testing procedure was
reported previously (Osawa et al., 2011b). The ICC for test–
retest reliability of the sit-up test was r 5 0.91.
Physical activity and nutritional assessment during the trial
The food intake of participants was assessed by a food
frequency questionnaire based on Food Groups (FFQg) software version 2.0, which is an optional software of ‘‘Excel Eiyokun’’ (Kenpaku-sha, Tokyo, Japan) that conforms to the Fifth
Edition of Standard Tables of Food Composition in Japan
compiled by the resources research committee of the Science
and Technology Agency (Tokyo, Japan) (Takahashi et al.,
2001). The FFQg was conducted before, after the seventh
week of training, and during the last training week.
Physical activity of each participant was assessed using a
uniaxial accelerometer (Lifecorder EX, Suzuken Co. Ltd.,
Nagoya, Japan) for at least 1 week, including 5 weekdays
and 2 weekend days, once before the trial and again around
the time of the last training week. Mean total step counts per
day were used for further analyses.
Statistical analyses
Group differences in age, body mass, BMI, total physical
activity, and the results of the FFQg at baseline were determined by the unpaired t-test. Normality and equal variance
assumptions were performed using the Kolmogorov–Smirnov
and Levene tests, respectively. If normality and equal variance
were assumed, longitudinal changes in all outcomes were
compared within the groups using two-way ANOVA (group
time) with repeated measurements; otherwise, the percentage
change from baseline values was tested using either the
unpaired t-test or one-way ANOVA. If an F-value was found
to be significant, preplanned contrast analyses (Bonferroni
correction) were performed to evaluate the significance of time
effects and differences between groups. A selective bivariate
relationship (between percent change in muscle force/torque,
muscle CSA, and EMG amplitude) was investigated using
Pearson’s correlation coefficient. PASW software version 18.0
for Macintosh (SPSS Inc., Tokyo, Japan) was used for all
statistical analyses. The level of significance was set at
Po0.05, and all values are presented as the mean SD.
Results
Participant baseline characteristics
The characteristics of the participants are summarized in Table 2. No significant differences between the
RT-WBV and RT groups at baseline were observed
in any of the evaluated characteristics, except the
CSA of erector spinae muscle. In addition, with the
exception of six individuals (RT-WBV, M: 2, F: 2;
RT, M: 1, F: 1) who had once engaged in regular RT
as part of a college sports team, all participants were
novices for RT.
One male in the RT-WBV group dropped out of
the study after the mid-training tests due to conflicts
with his job; however, the other participants completed the 13-week training program and all of the
evaluation tests (Fig. 1).
Muscle activity during exercise
sEMG signals from the VM and VL muscles recorded during Bulgarian squat exercise illustrate the
differences in muscle activity for contractions performed in the presence and in the absence of WBV
(Fig. 2). In the RT group, the EMG signals from VM
and VL showed 44.6 14.3% and 49.3 21.4%
maximal voluntary contraction (MVC), respectively,
during exercise, while the total duration that the
signals did not reach 40% MVC was 42 and 36 s,
respectively, during the 80 s period that each exercise
set was performed (Fig. 2a). In contrast, the EMG
Table 2. Participant characteristics
Characteristic
RT-WBV, n 5 16
(F:14, M:2)
RT, n 5 16
(F:13, M:3)
Age (years)
Height (cm)
Body mass (kg)
BMI (kg/m2)
Total physical activity
(steps/day)*
Total energy intake (kcal/day)
Protein (%)
Fat (%)
Carbohydrate (%)
36.8 8.4
161.2 6.4
55.3 8.8
21.1 2.3
10 565 2022
37.7 9.5
164 5.9
58.8 9.0
21.8 2.3
9248 3772
1856 366
13.1 1.3
29.9 7.0
56.2 5.6
2080 470
13.9 1.9
30.1 4.4
56.0 5.4
*Total physical activity was determined by the number of step counts per
day, as measured using a uniaxial accelerometer.
BMI, body mass index; RT, resistance training group; RT-WBV, resistance
training with whole-body vibration group.
5
Osawa & Oguma
Fig. 2. Typical surface electromyographic signals from the vastus medialis and vastus lateralis during Bulgarian squat exercise.
Signals were recorded during exercise combined without (a) or with (b) whole-body vibration (WBV), and an external load of
12 kg for female participants with 51 kg body mass. Signals were recorded from the first to last repetition of the eight-repetition
exercise.
Fig. 3. Representative axial magnetic resonance imaging (MRI) scans of the L4-5 disc space level at pre-training (a) and posttraining (b). Muscle hypertrophy in m. psoas major (10.7%, Po0.001) and erector spinae muscle (8.5%, P 5 0.001) occurred in
response to slow-velocity resistance training coupled with WBV. ES, erector spinae muscle; IABD, m. anterolateral abdominal
(obliquus internus abdominis1obliquus externus abdominis1transversus abdominis); MF, multifidus; PS, m. psoas major;
QL, quadratus lumborum muscle; RA, m. rectus abdominis.
signals, which were recorded with a band-stop filter,
from VM and VL in the RT-WBV group showed
48.9 11.7% and 52.4 20.9% MVC, respectively,
while the total duration that the signals did not reach
40% MVC was 21 and 30 s, respectively, during the
80 s period that each exercise set was performed.
CSA of abdominal muscles
To assess the effect of WBV on muscle hypertrophy,
participants of both training groups were subjected
to MRI testing before and after the 13-week training
period (Fig. 3). From the MRI images of the abdominal area, changes in the CSA of several target
muscles were determined and compared between
the two training groups. As shown in Fig. 4, a
significant group time interaction was observed
in the CSA of m. psoas major (P 5 0.03),
which significantly increased in both the RT-WBV
6
(110.7 5.3%, Po0.001) and RT groups (13.8 7.5%, P 5 0.045). A significantly higher percent
change increase in erector spinae muscle in the RTWBV group was also detected compared with that of
the RT group (P 5 0.04, unpaired t-test). In addition,
although no significant group time interactions
were found in the CSA of m. rectus abdominis
(P 5 0.85) or IABD (P 5 0.53), significant time effects were observed in both these muscles (Po0.001
and P 5 0.002, respectively). Finally, no significant
group time interactions were detected in the CSA
of quadratus lumborum (P 5 0.94) or multifidus
muscles (P 5 0.86).
Countermovement-jump test
Changes in muscle power were evaluated using the
countermovement-jump test, which revealed significant group time interactions in jump height
Vibration training effects on muscle fitness
Fig. 4. Sizes of cross-sectional areas at the L4-5 disc space level determined from magnetic resonance imaging (MRI)
performed pre-training and post-training. All values are presented as the mean SD. Black bars represent the resistance
training with whole-body vibration group (RT-WBV), whereas white bars represent resistance-training group (RT). ES, erector
spinae muscle; IABD, m. anterolateral abdominal (obliquus internus abdominis1obliquus externus abdominis1transversus
abdominis); MF, multifidus; PS, m. psoas major; QL, quadratus lumborum muscle; RA, m. rectus abdominis. wSignificant
group time interaction (Po0.05, two-way repeated-measures ANOVA). *Significant difference (Po0.05, Bonferroni
correction). zSignificant time effect (Po0.05, two-way ANOVA). §Significant difference was observed between the groups
at baseline (unpaired t-test).
(Table 3). A comparison of the mean pre-treatment
and post-treatment values revealed that significant
increases in jump height occurred in both the RTWBV (115.0 10.5%, P 5 0.005) and RT groups
(111.3 8.2%, P 5 0.001).
EMGrms during isometric extension in VM
(P 5 0.012) (Fig. 5). In addition, no group time
interactions were detected in the EMGrms of VL
(P 5 0.54); however, significant time effects were
observed (Po0.001) between the pre-training and
mid-training (P 5 0.014) and pre-training and posttraining (P 5 0.01) sEMG measurements.
Maximal voluntary isometric knee extension force
A significant group time interaction was also observed in maximal isometric knee extension force
(Table 3), as marked increases in strength from pretraining levels were observed following the 13-week
training in both the RT-WBV (163.5 53.9%,
Po0.001) and RT groups (125.6 13.9%,
P 5 0.001). Notably, maximal isometric knee extension force was significantly higher in the RT-WBV
group than the RT group at both the mid-training
and post-training evaluation points (P 5 0.009 and
Po0.001, respectively).
sEMG
To examine the intensity of muscle contractions
under the two training conditions, sEMG signals
from the VM and VL muscles were monitored during
the maximal isometric extension force test. A significant group time interaction was observed in the
Maximal isokinetic strength tests
As was observed for isometric knee extension force, a
significant group time interaction was also detected in maximal concentric knee extension torque
(Table 3). A comparison of the pre-training and posttraining strengths revealed a significant increase in
the RT-WBV group (176.7 53.8%, Po0.001),
whereas no significant changes were found in the
RT group (117.8 27.8%, P 5 0.18). The analysis
also demonstrated that maximal concentric knee
extension torque was significantly higher in the RTWBV group than the RT group after completion of
the 13-week training program (P 5 0.007).
In contrast to concentric knee torque, no group time interactions were observed in maximal eccentric
knee extension torque (Table 3); however, a significant time effect was found (Po0.001). Similar results
were observed for the local muscle endurance, as no
7
Osawa & Oguma
Table 3. Effects of whole-body vibration on performance tests
RT-WBV (n 5 16)
CMJ (cm)
Pre
24.5 8.6
Mid
26.9 8.5
Post
27.9 8.6
ISOM-K (N/kg)
Pre
5.7 1.4
Mid
7.6 1.2
Post
8.8 1.1
CON (N m/kg)
Pre
1.1 0.2
Mid
1.6 0.4
Post
1.9 0.5
ECC (N m/kg)
Pre
1.9 0.4
Mid
2.2 0.5
Post
2.5 0.6
TW (J)
Pre
1036 374
Mid
1126 333
Post
1242 445
MP (W)
Pre
34.1 11.9
Mid
34.8 10.7
Post
39.6 13.3
ISOM-L (N m/kg)
Pre
3.4 1.2
Mid
4.5 1.4
Post
4.9 1.4
Sit-up (times)
Pre
15.0 6.7
Mid
20.9 6.3
Post
23.9 7.0
RT (n 5 16)
P-value
23.4 7.0
24.4 7.4
25.8 6.9
*
5.5 0.8
6.4 1.3
6.8 1.2
***
1.3 0.2
1.5 0.5
1.5 0.4
***
1.9 0.5
2.1 0.5
2.2 0.5
1213 461
1266 546
1344 478
***
36.9 14.5
42.4 17.1
41.9 15.2
3.4 1.2
3.8 1.2
4.1 1.2
**
15.9 5.4
21.0 7.7
23.6 7.6
Significant group time interactions are marked as follows:
*Po0.05; **Po0.01; ***Po0.001.
Pre, pre training program; Mid, post 7-week training period; Post, post
13-week training period; CMJ, countermovement-jump height; CON,
concentric contraction; ECC, eccentric contraction; ISOM-K, isometric
knee extension force; ISOM-L, isometric lumbar extension torque; MP,
mean power in endurance test; RT, resistance training; RT-WBV,
resistance training with whole-body vibration; TW, total work in endurance test.
group time interactions were observed in total
work (J) or mean power (W) (Table 3), although
the time effects were found to be significant for both
total work (P 5 0.003) and mean power (P 5 0.002)
on comparison of pre-training and post-training
levels.
Trunk muscle strength and endurance
The final performance tests measured isometric lumbar extension strength and abdominal muscle endurance. A significant group time interaction was
observed in the isometric lumbar extension torque,
with both the RT-WBV and RT groups displaying
marked increases in post-training muscle strength
compared with baseline values (151.5 34.1%,
Po0.001 and 126.4 17.5%, Po0.001, respectively) (Table 3). The evaluation of abdominal
8
Fig. 5. Effects of whole-body vibration (WBV) on surface
electromyography activities during the maximal isometric
knee extension strength test. Measurements were made in the
pre-training period (Pre), after 7 weeks of training (Mid),
and at the completion of the 13-week training program
(Post). All values are presented as the mean SD. Black
bars represent the resistance training with WBV group (RTWBV), and white bars represent resistance training group
(RT). VL, vastus lateralis; VM, vastus medialis. wSignificant
group time interaction (Po0.05, two-way repeated-measures ANOVA). *Significant difference (Po0.05, Bonferroni
correction). zSignificant time interaction (Po0.05, two-way
repeated-measures ANOVA).
muscle endurance revealed that both groups had
significant increases in the number of sit-ups performed with respect to time (Po0.001). However,
the observed changes in abdominal muscle endurance did not represent significant group time interactions (Table 3).
Anthropometry, physical activity, and nutritional
assessment
No significant group time interactions were observed in the body mass (P 5 0.50), total energy
intake per day (P 5 0.83), or the ratio (%) of protein:fat:carbohydrate consumed during the trial; protein (P 5 0.43), fat (P 5 0.17), and carbohydrate
(P 5 0.41). In addition, no group time interactions
were observed in physical activity (P 5 0.13); however, physical activity significantly differed between
the pre-training and post-training levels (P 5 0.01).
Correlation analyses
A significant correlation was observed between percent change in maximum isometric knee extension
force and EMG activity in the RT-WBV group
(r 5 0.67, Po0.001). However, no significant correlation was found between the percent change in
muscle force/torque and CSA [lumbar extension
torque and erector spinae muscle (r 5 0.42,
Vibration training effects on muscle fitness
P 5 0.11); m. psoas major and countermovementjump (r 5 0.35, P 5 0.28)]. In the RT group, no
significant correlations were observed between the
percent change in muscle force/torque and EMG
activity or muscle CSA.
Discussion
In our randomized controlled study composed of
healthy, untrained adults, a 13-week slow-velocity
RT program involving light external loading combined with WBV resulted in considerable gains in the
CSA of abdominal muscles, and increases in maximal isometric knee extension force, isokinetic knee
extension torque, isometric lumbar extension torque,
countermovement-jump height, and EMG activities
compared with the identical RT without WBV. The
present results suggest that WBV has marked additional effects on muscle hypertrophy and strength in
abdominal muscles, and may be suitable for combining with slow-velocity RT involving exercises of long
duration ( 80 s).
The RT regimen used in this study consisted of
eight different lower extremity and trunk muscle
exercises performed for 80 s with slow velocity, with
the exception of the roll back and hip walking
exercises that were performed continuously for 64
and 48 s, during an approximately 60 min session.
Marked effects on muscle strength and power were
also reported in the study conducted by Delecluse et
al. (2003), who utilized a 20 min WBV-RT program
composed of 60 s body-weight exercises with 5 s
intermittent rest periods over a 12-week period. In
the RT regimens used by researchers who did not
find any additional effects of WBV on muscle
strength and power, either light exercises with low
volume (5–8 min/session) or high-intensity training
with short-exercise duration (approximately 30 s/set)
were performed (de Ruiter et al., 2003; Ronnestad,
2004; Kvorning et al., 2006; Carson et al., 2010; von
Stengel et al., 2010). These findings suggest that the
additional effects of WBV may be dependent on the
training regimen, particularly the duration of WBV
exposure and the intensity of training.
In addition to including exercises of longer duration, our training regimen was designed to examine
the influence of external weight loading and exercise
position on the augmentation of WBV effects on
muscle. Two studies have reported that the frequency
and amplitude of vibration platforms or additional
weight loading have effects on force generation (Pel
et al., 2009; Rittweger, 2010). We confirmed previously that force generation increases when weight is
loaded on the vibration platform (Osawa et al.,
2011b). Our present results indicate the possibility
that light external weight loading would be suitable
for exercise protocols combined with WBV (frequency, 35 Hz; amplitude, 2 mm) in individuals
with normal body mass. Furthermore, our training
regimen mainly consisted of exercises performed in
prone and supine positions, resulting in close proximity of the trunk muscles to the WBV source with
minimal dampening. Although the optimal relationship between vibration parameters, weight conditions (total mass of body mass and additional
weight), and exercise position remains unclear, these
factors appear to be related with the marked muscle
fitness improvements associated with WBV.
The observed effects of WBV on muscle hypertrophy may involve a number of physiological mechanisms. First, the exogenous stimulation of skeletal
muscle with vibration may contribute to increases
in muscle mass. This speculation is supported by the
study of Xie et al. (2008), who found that daily
(15 min/day) WBV exposure for 8 weeks (5 days/
week) without any exercises or stretching led to
increases of 24% and 29% in type I and II fibers,
respectively, in soleus muscles compared with agematched controls. Second, WBV might enhance the
effects of RT on muscle hypertrophy by augmenting
muscle activity. It has been suggested that WBV
leads to increases in exercise-induced growth hormone responses via activation of the hypothalamus–
pituitary axis by afferent signals from both muscle
metaboreceptors and mechanoreceptors (Kjaer,
1992; Rittweger, 2010). It has also been proposed
that WBV leads to muscle deoxygenation, which is
associated with the production of free radicals and
reactive oxygen species, stimulating satellite cells to
regenerate muscle fibers (Anderson, 2000; Yamada et
al., 2005). Although it is suggested that a continually
generated MVC of 440% during exercises is necessary for muscle growth (Tanimoto & Ishii, 2006), we
found that muscle contractions during exercise with
WBV were occasionally o40% MVC after applying
a band-stop filter. Although the application of bandstop filters will result in an underestimation of the
true magnitude of neuromuscular responses to WBV,
muscle activities with WBV after filtering of the
EMG signals remained higher than those without
WBV during exercise. In addition, a recent study
measuring muscle length and EMG activity during
exercise with WBV has shown that EMG changes
precede muscle lengthening (Cochrane et al., 2009),
suggesting that stretch reflex would occur on exposure to WBV. Although further studies are needed to
provide mechanistic insights for the additional effects
of WBV on muscle hypertrophy (e.g., protein turnover and/or intracellular anabolic signaling from
muscle biopsies), our results suggest that WBV leads
to additional gains in muscular CSA.
In line with the induction of muscle hypertrophy
resulting from WBV, maximal isometric and
9
Osawa & Oguma
concentric contractions, in addition to power, were
also increased by incorporating WBV into the
13-week RT regimen. Notably, however, maximal
eccentric contraction and local muscle endurance
were not noticeably affected by WBV. The finding
that additional WBV effects were observed only in a
few muscle performance gains might be attributable
to the higher sensitivity of the neuromuscular systems involved in isometric and concentric contractions, and countermovement-jump to WBV, leading
to increased co-activation of a–g motor neurons
(Burke et al., 1978; Romano & Schieppati, 1987;
Kouzaki et al., 2000; Fallon & Macefield, 2007). As
an earlier study found that exercise with vibration
significantly improved maximal force (149.8%) after
a 3-week training period, it has been suggested that
RT combined with WBV would lead to increases
in muscle strength primarily due to enhancement of
neural factors (Issurin et al., 1994). We detected
a significant correlation between elevated EMG
amplitude and knee extension force gain in the RTWBV group. The elevated EMG activity reflects
increased recruitment and firing rate of motor units,
and would contribute to increased muscle force
(Suzuki et al., 2002). In contrast, we did not detect
a correlation between the increase in the CSA of m.
psoas major and countermovement-jump height
improvement, which may have been due to the
numerous skeletal muscles that contribute to the
movement, or between the increase in the CSA of
erector spinae muscle and lumbar extension torque
gain. As we did not observe muscle hypertrophic
effects on lower extremity muscles or on neural
improvement in abdominal muscles, we could not
provide solid evidence for the contribution of muscle
hypertrophy on the observed strength gains. However, the present results suggest that the observed
strength gains might be attributable to the stimulation of neural factors by WBV.
In the present study, weight loading was based on
individual body mass due to safety concerns that
untrained individuals could correctly perform the
target exercises on the moving vibration platform
with standardized weight limits. Under unstable
conditions, there was also concern that certain participants might perform exercises without adequate
training intensity, resulting in variations in muscle
strength and power gains in the RT-WBV group.
However, in both training groups, participants perceived the exercises as physically demanding
and experienced fatigue, light to moderate delayed
onset of muscle soreness following each training
session, and improved muscle fitness. Thus, we
have confidence that the training intensity was properly configured in this study, a speculation that is
supported by the muscle fitness gains observed in
both groups.
10
Several limitations of this study should be considered when interpreting and generalizing the findings
presented here. First, we did not obtain MRI data
from quadriceps muscles due to budget restraints.
Second, EMG was not applied to the evaluation of
antagonist muscles and the power and trunk muscle
strength tests due to a lack of instruments for
synchronizing muscle power and EMG signals, and
because the waist pad of the lumbar extension
machine was located at an identical level as the
electrode positions. Finally, although the participants were randomly assigned to training groups
stratified by age and sex, the study consisted predominantly of women with a relatively wide range of
ages. As age and sex might be effect modifiers of
muscle strength and power gains, a larger study size
with a higher proportion of men and smaller age
range is needed to confirm that the observed increases in strength are applicable to both males and
females.
In conclusion, we have demonstrated that a 13week RT program combined with WBV leads to
considerable gains in the CSA of abdominal muscles,
maximal isometric and concentric knee extension
strengths, isometric lumbar extension strength, and
countermovement-jump height over baseline values
in untrained adults compared with the identical
training lacking WBV. In particular, the WBV-induced increases in the CSA of m. psoas major and
erector spinae muscle, and the maximal isometric
lumbar extension strength gains, suggest that incorporation of WBV into RT programs may be beneficial for the prevention and rehabilitation of chronic
low back pain.
Perspectives
Our findings confirm that intentional slow-velocity
RT combined with WBV has marked training effects
on muscle hypertrophy, strength, and power in
healthy, untrained adults. The combined training
method takes advantage of the force generated by
the vibration platform (Rittweger, 2010) and stimulation of the tonic vibration reflex response in
muscles (Hagbarth & Eklund, 1966). In future
studies, it would be interesting to determine whether
the efficacy of vibration is increased when combined
with RT exercise protocols that subject muscles to
increasing time under tension. In practical applications, the significant increases in the CSA of m.
psoas major muscle and the ability to obtain higher
maximal isometric lumbar extension torque with
vibration may be beneficial for the prevention of
sarcopenia and rehabilitation of low back pain,
which is associated with the deterioration of these
parameters (Cassisi et al., 1993; Barker et al., 2004).
Vibration training effects on muscle fitness
As RT with WBV has also been shown to relieve
chronic low back pain sensation in the elderly
(Iwamoto et al., 2005), our promising results
support the need to further investigate the
effects of WBV on chronic musculoskeletal pain
sensation and strength in young to middle-aged
individuals.
Key words: muscle mass, vibration, novice, platform,
trunk muscle, training program, neural adaptation.
Acknowledgement
This study was supported by the Keio University Doctoral
Student Grant-in-Aid Program, 2009.
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