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Gravitational forces and whole body vibration: Implications for prescription of vibratory stimulation


Abstract and Figures

The purpose of this study was to determine the gravitational forces (g-forces) associated with different postures (standing single leg, standing double leg, semi-squat), amplitudes (1.25, 3.0, 5.25 mm), frequencies (10, 20, 30 Hz) and at different anatomical sites (tibial tuberosity, greater trochanter, jaw). Twenty-three subjects underwent whole body vibratory stimulation on a teetering platform that oscillated about a sagittal shaft (Galileo™ 2000). The analysis involved collapsing all the data into four categories (frequency, amplitude, posture, damping) and investigating the g-forces within each category. The 20 Hz frequencies resulted in significantly greater g-forces (2.05g) than 10 and 30 Hz (1.83 and 1.76g, respectively). As amplitude increased so to did the g-forces (1.25 mm, 1.6g; 3.0 mm, 1.85g; 5.25 mm, 2.2g; P
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Gravitational forces and whole body vibration: implications
for prescription of vibratory stimulation
Blair Crewther*, John Cronin, Justin Keogh
Division of Sport and Recreation, Sport Performance Research Centre, Auckland University of Technology,
Private Bag 92006, Auckland 1020, New Zealand
Received 7 April 2003; revised 9 October 2003; accepted 3 November 2003
The purpose of this study was to determine the gravitational forces (g-forces) associated with different postures (standing single leg,
standing double leg, semi-squat), amplitudes (1.25, 3.0, 5.25 mm), frequencies (10, 20, 30 Hz) and at different anatomical sites (tibial
tuberosity, greater trochanter, jaw). Twenty-three subjects underwent whole body vibratory stimulation on a teetering platform that oscillated
about a sagittal shaft (Galileoe2000). The analysis involved collapsing all the data into four categories (frequency, amplitude, posture,
damping) and investigating the g-forces within each category. The 20 Hz frequencies resulted in significantly greater g-forces (2.05g) than 10
and 30 Hz (1.83 and 1.76g, respectively). As amplitude increased so to did the g-forces (1.25 mm, 1.6g; 3.0 mm, 1.85g; 5.25 mm, 2.2g;
P,0:05). G-forces associated with the semi-squat (2.34g) were significantly greater ðP,0:001Þthan the standing postures. Significant
damping was observed as the vibratory stimulation was transmitted to the proximal segments (tibial tuberosity, 3.91g; greater trochanter,
1.26gand jaw, 0.34g). Findings were discussed in terms of safe, progressive and effective prescription of vibratory stimulation.
q2003 Elsevier Ltd. All rights reserved.
Keywords: Gravitational forces; Vibration; Damping
1. Introduction
Vibration has been widely used as a tool for rehabilita-
tion, enhancing physical performance and stimulating bone
development. Vibration has been used in the treatment of
patients with spasmodic torticollis (Karnath et al., 2000), the
rehabilitation of neck muscles following spatial neglect
(Schindler et al., 2002) and in the treatment of pain
(Lundeberg, 1984; Lundeberg et al., 1987a,b). Although,
these studies involved the direct application of vibration,
recent research has shown that whole body vibration (WBV)
interventions may also be an effective rehabilitation tool.
Two months WBV has been shown to improve lower limb
neuromuscular function, as demonstrated by improved co-
ordination and balance of 35 elderly subjects performing a
standardised chair-rising test (Runge et al., 2000). Well-
controlled WBV may also assist in the treatment of lower
back pain (Rittweger et al., 2002) and in the treatment of
patients with spinal chord injuries (Gianutsos et al., 2000).
There is a growing body of evidence both anecdotal and
scientific, which suggests that WBV can be used as a
performance-enhancing tool. Many studies have examined
the influence of WBV upon physical performance (Bosco
et al., 1998a,b, 1999a,c, 2000; Rittweger et al., 2000;
Torvinen et al., 2002a,b; Warman et al., 2002). In most
cases, vibration has been shown to positively influence
maximal strength and force output (Bosco et al., 1999c;
Warman et al., 2002), power output (Bosco et al., 1998b,
1999c, 2000) and vertical jump height (Bosco et al., 1998a,
2000; Torvinen et al., 2002a). In general, research in this
area is characterised by frequencies of 25 50 Hz and
amplitudes ranging from 1 to 10 mm, resulting in g-forces
of 3–7g.
The application of WBV for bone development is
another area gaining considerable interest. The use of
WBV has been found effective in the prevention of bone
loss and/or increasing bone density within various animal
models (Rubin et al., 1995, 2001, 2002; Flieger et al., 1998;
Judex et al., 2001, 2002). Considering its stimulatory effect
upon bone this tool may be a potential treatment
for osteoporosis and other related bone disorders.
Rubin et al. (1998) investigated the ability of WBV to
1466-853X/$ - see front matter q2003 Elsevier Ltd. All rights reserved.
Physical Therapy in Sport 5 (2004) 37–43
*Corresponding author. Tel.: þ649-917-9999x7119; fax: þ649-917-
E-mail address: (B. Crewther).
inhibit post-menopausal osteopenia. Thirty-one women
underwent mechanical vibration of the lower body for 12
months (20 min/day). Loss of bone mineral density (BMD)
of the trochanter region of the hip was significantly less in
the treated group (20.8%) as compared to the placebo
group (23.3%). Ward et al. (2001) also reported a net
increase in tibial BMD (18.2 mg/ml) and spinal BMD
(3.8 mg/ml) among cerebral palsy children, after 6 months
vibration treatment. A recent study by Pitukcheewanont
et al. (2002) reported significant increases in cancellous
BMD (5.95%) and cortical BMD (1.21%) after only 8 weeks
of vibration treatment. Research investigating the stimu-
latory effects of WBV upon bone have employed vibration
frequencies in the range of 30 90 Hz and accelerations of
The frequency and amplitude of vibration, duration of
exposure and the posture adopted during WBV are all
factors that need to be considered when prescribing WBV,
as the interaction of these factors affects will determine the
magnitude of the g-forces and thus nature of the training
stimulus. The application of WBV also has many potential
side effects. Though mechanical vibration may not elicit
those negative effects commonly associated with occu-
pational vibration, various ill effects such as itching,
erythema and oedema have been reported (Pope et al.,
1996; Rittweger et al., 2000). A recent study investigated
the effects of WBV (frequency, 26 Hz; amplitude, 6 mm,
6g) upon muscle stiffness (Cronin, Oliver and McNair,
unpublished data). This study replicated an intervention
cited previously (Bosco et al., 1999a), that is, 5 £60 s of
unilateral vibratory stimulation with 60 s rest between
interventions. During and/or following treatment a number
of the subjects experienced pain in the jaw, neck, and lower
extremity, particularly tibialis anterior, some of these
injuries requiring physiotherapy treatment. It was suggested
that more research be conducted on the effects of different
WBV protocols and a dose-response model formulated.
Such an analysis would provide valuable information in
terms of the forces developed and transmission of forces
under different vibration conditions, thereby assisting in the
development of both safe and effective protocols. Therefore,
the aim of this study is to investigate the g-forces associated
with sinusoidal WBV and the influence of amplitude,
frequency and posture upon the development and trans-
mission of these forces.
2. Methodology
2.1. Participants
Twenty-three subjects (11 males and 12 females)
volunteered to participate in this study. Subject mean age
and mass were (26.1 ^5.4 years) and (69.6 ^12.2 kg),
respectively. Subjects were screened to ensure that they
were free from the following conditions: pregnancy, acute
thromboses, acute inflammations, implants, fractures, acute
tendinopathies, kidney or bladder stones and gallstones (as
per manufacturers instructions). All subjects signed an
informed consent form prior to involvement in this research.
The Human Subject Ethics Committee, Auckland Univer-
sity of Technology, approved all the procedures undertaken.
2.2. Equipment
Subjects were exposed to vertical sinusoidal WBV using
the Galileoe2000 (Novotec GmbH, Germany). In effect,
the Galileo is a mechanical teeterboard, that is, the teetering
surface oscillates about a sagittal shaft (Fig. 1). The
Galileoe2000 has a vibration range of 0 30 Hz and an
amplitude range of 1.0 5.2 mm. A 10glinear accelerometer
(Sensotec, Ohio), instrumented with an on-line amplifier
(^5 V), was used for data collection. Data was sampled at
1000 Hz with a custom-made data acquisition and analysis
program (LabViewe). Data was filtered using a low pass
Hamming filter (cut-off frequency 6 Hz) and full-wave
rectified prior to data analysis.
2.3. Procedure
Subjects completed a standardized warm-up prior to
testing. This consisted of a 3-min cycle (60 rpm) followed
by light stretches for the quadriceps, hamstrings and calf
muscle groups, with each stretch held for 15 s. The
accelerometer was then attached to the tibial tuberosity,
greater trochanter and jaw of each subject (via an ice block
stick clenched between the jaw). To prevent excessive
oscillation at the head, subjects were required to look
directly forward throughout testing. The accelerometers
were aligned vertically, so as to record the vertical
accelerations at each site. Attachment of the accelerometer
to the lower limb sites was accomplished using industrial
strength tape, then reinforced with strapping tape to ensure
the accelerometer was secure.
Fig. 1. Whole body vibration device (Galileoe2000).
B. Crewther et al. / Physical Therapy in Sport 5 (2004) 37–4338
Subjects were assessed in three postures: standing double
leg (SDL), standing single leg (SSL) and a semi-squat (SS).
The SDL required subjects to stand in a relaxed position
with knees slightly flexed (i.e. 3 58from lockout). The SSL
required subjects to adopt the SDL before taking their
bodyweight on their right limb. In the SS subjects adopted a
squat position with their knees flexed at 1208, measured with
a manual goniometer. All postures were performed with the
trunk in a vertical position. Each posture was assessed at
three separate foot positions (2 4) on the teeterboard,
equating to distances of 5, 15 and 25 cm, respectively, from
the sagittal axis. Thus, amplitude associated with the
different foot positions also increased (2 1.25 mm, 3
3.0 mm, 4 5.25 mm). Heels remained in contact with the
vibration surface throughout all assessments. Each posture
and position was further assessed at three different vibration
frequencies (10, 20 and 30 Hz). Trials were randomised to
negate any order effects, with data collected for a period of
5 s with 20 s recovery between trials. Subjects were allowed
to use the machine handrails but only to maintain their
balance. Any unusual reactions or side effects to testing
were also reported. Suitable footwear was worn for all the
assessments. Acceleration data was also collected from the
surface of the vibration machine at the different foot
positions ( £3) and vibration frequencies ( £3).
2.4. Statistical analysis
Data was collapsed into four categories for analysis: (1)
frequency effect, 10, 20 and 30 Hz vibration frequencies; (2)
amplitude effect, foot positions 2–4; (3) posture effect,
double leg standing, single leg standing and a semi-squat;
and (4) damping effect, tibial tuberosity, greater trochanter
and jaw. Mean values within each of these categories were
analysed using a repeated measure ANOVA. Fratios were
considered significant at P,0:05:If significant inter-
actions were present Tukey post-hoc comparisons were
3. Results
Data was collapsed to explain each effect (frequency,
amplitude, posture or damping). For example, frequency data
was determined from the combined values of amplitude
(£3), posture ( £3) and site ( £3). The g-forces measured
at the surface of the vibration machine are depicted in Table 1.
An increase in amplitude (from position 2 to 3 to 4) resulted
in a slight increase in g-forces at the lowest vibration
frequency (9.679.74g). This increase became more promi-
nent as frequency increased from 20 Hz (9.76 –10.14g), with
a further increase noted at 30 Hz (9.91 10.88g).
The g-forces associated with three different vibration
frequencies can be observed in Table 2. A significant main
effect ðF¼6:64;P¼0:003Þwas noted with the g-forces
associated with 20 Hz vibrations being significantly greater
than that found at 10 or 30 Hz. The power of the performed
test with
¼0:050 was 0.843.
The g-forces related to the different foot positions are
shown in Table 3. A significant main effect was observed
ðF¼31:2;P,0:001Þ:Post-hoc comparisons revealed that
greater g-forces were experienced with increasing distance
from the central axis of the teeterboard. The power of the
performed test with
¼0:050 was 1.00.
The g-forces related to the different postures are
detailed in Table 4. A significant main effect for posture
ðF¼43:4;P,0:001Þwas noted, with the g-forces associa-
ted with the SS significantly greater than both the standing
postures. The power of the performed test with
was 1.00.
The g-forces associated with the different positions that
the accelerometer was attached, can be observed in Table 5.
Table 1
Gravitational forces (vibration surface) associated with different vibration
frequencies and different foot positions
10 Hz 20 Hz 30 Hz
2 (1.25 mm) 9.67 9.76 9.91
3 (3 mm) 9.71 9.95 10.38
4 (5.25 mm) 9.74 10.14 10.88
Table 2
Gravitational forces associated with different vibration frequencies
10 Hz 20 Hz 30 Hz
Mean (g-force) 1.83 2.05
SD 0.37 0.32 0.40
SEM 0.08 0.07 0.09
Range 1.20– 2.50 1.40 –2.60 0.90 –2.60
Significantly greater than the 10 and 30 Hz frequencies ðP,0:05Þ:
Table 3
Gravitational forces associated with different foot positions
2 (1.25 mm) 3 (3 mm) 4 (5.25 mm)
Mean (g-force) 1.60 1.85
SD 0.29 0.35 0.41
SEM 0.06 0.08 0.09
Range 1.10– 2.20 1.00–2.50 1.50 –3.10
Significantly greater than position 2 ðP,0:05Þ:
Significantly greater than position 2 and 3 ðP,0:05Þ:
Table 4
Gravitational forces associated with different postures
Standing Single leg Semi-squat
Mean (g-force) 1.62 1.69 2.34
SD 0.38 0.27 0.40
SEM 0.08 0.06 0.09
Range 0.90– 2.20 1.20 –2.20 1.69 3.20
Significantly greater than standing and single leg postures ðP,0:05Þ:
B. Crewther et al. / Physical Therapy in Sport 5 (2004) 37–43 39
The g-forces decreased with increasing distance from the
vibrating platform ðF¼283:7;P,0:001Þ:The power of
the performed test with
¼0:050 was 1.00.
4. Discussion
4.1. Frequency effect
The g-forces associated with 20 Hz vibrations (2.05g)
were significantly greater than both the 10 Hz (1.83g) and
30 Hz (1.76g) frequencies (Table 2). A reduction in force
transmission above frequencies of 16 20 Hz has been
previously reported (Harazin and Grzesik, 1998; Mester
et al., 1999). Harazin and Grzesik (1998) found that the
vibration magnitudes being transmitted by the hip, shoulder
and head decreased with an increase in frequency above 16 –
20 Hz. Mester et al. (1999) proposed that with increasing
vibration frequency the onset of active damping might be
observed with a decrease in force transmission. Thus, at
higher frequencies (i.e. .20 Hz) the transmission of
vibratory-induced forces would decrease, hence the lower
g-forces occurring at 30 Hz. Resonant frequencies up to
20 Hz have been identified for the organs, head and the
eyeballs, therefore, active damping may occur to prevent
excessive acceleration at these sites (Mester et al., 1999). In
response to greater vibration frequencies, coupled rotational
motions about the hip joint (Matsumoto and Griffin, 1998),
body sway (Mester et al., 1999) or greater muscle activation
(Mester et al., 1999) may also affect the transmission of
vibratory-induced forces. As exposure to WBV elicits other
neural, biological and biomechanical responses (Seidel and
Griffin, 1998; Bosco et al., 1999b) determining the exact
mechanism of the frequency effect (i.e. greater g-forces at
20 Hz) remains difficult. It would seem, however, that
frequencies of approximately 20 Hz result in maximal g-
forces. In terms of exercise prescription it would seem that
lower (10 Hz) and/or higher frequencies (30 Hz) should be
used with novice or untrained individuals due to the lower g-
forces associated with these frequencies. Utilisation of WBV
at 20 Hz is more likely to induce injury and should be
used with individuals that are conditioned to tolerate higher
4.2. Amplitude effect
A significant main effect was observed in relation to the
different foot positions (Table 3). That is, greater mean g-
forces were experienced with increasing distance from the
central axis of the teeterboard from position 2 (1.6g)to
positions 3 (1.85g) and 4 (2.2g), respectively. In terms of
prescribing WBV it would seem prudent to use foot position
2 (amplitude 1.25 mm) as an initial training stimulus due to
the significantly lower g-forces associated with this
position. As familiarity and adaptation occurs, the vibratory
stimulus may be progressively overloaded by moving the
foot positions distally from foot position 3 (3.0 mm) to foot
position 4 (5.25 mm), thereby progressively increasing the
associated g-forces. However, we can only speculate as
when best to progressively overload frequency and
amplitude as research investigating the overloading of
these factors appears non-existent. Biological or biomecha-
nical markers that indicate the individuals readiness for
WBV overload need to be identified and should be the
subject of future research.
4.3. Posture effect
The g-forces associated with the semi-squat (2.34g) were
significantly greater than the standing postures (Table 4). It
is speculated that greater muscle activation in this posture
would increase muscular stiffness, thereby enhancing the
transmission of vibratory forces throughout the body.
Greater force transmission may also result when a structure
is vibrated at or near its resonance frequency (Seidel and
Griffin, 1998), though such notion is limited in this context
given that the g-forces occurring at each frequency was
combined to provide absolute values for each posture.
Nonetheless, the results of this study suggest enhanced force
transmission in the semi-squat compared to the single and
standing postures. Previous research has indicated that a
bent knee position attenuates force transmission into the hip
and upper body (Lanyon, 1992; Pope et al., 1996;
Matsumoto and Griffin, 1998). The different findings may
be attributed to methodological differences between studies
(i.e. skin vs. skeletal accelerometer, accelerometer position,
vibration protocols). The discrepancy found with previous
authors may be further explained by the fact that heels
remained in contact with the teeterboard. Given that only
one previous study used a teeterboard-vibrating machine
(Pope et al., 1996) as per this study and that study assessed
only a small sample size ðn¼5Þ;determining the influence
of posture upon force transmission remains difficult. The
findings of this study would suggest, however, that a
continuum of postures beginning with bilateral standing and
progressing to unilateral standing and bilateral semi-
squatting would be the safest manner in which to progress
Table 5
Gravitational forces associated with different body positions
Jaw Greater trochanter Tibial tuberosity
Mean (g-force) 0.34 1.26
SD 0.13 0.65 0.59
SEM 0.03 0.13 0.13
Range 0.14– 0.55 0.70 –3.20 2.50– 5.20
Significantly greater than the jaw ðP,0:05Þ:
Significantly greater than the jaw and the greater trochanter ðP,0:05Þ:
B. Crewther et al. / Physical Therapy in Sport 5 (2004) 37–4340
4.4. Damping effect
As expected, greater forces were observed at the sites
located closer to the vibration surface (Table 5). The g-
forces measured at the lowest site (3.91g) also revealed a
large damping effect from those forces developed at the
vibration surface (Table 1). Though, the propagation of
vibratory forces throughout the body is largely deter-
mined by the damping effect of the soft tissues and body
parts, other factors add to the complexity of this issue.
Exposure to sinusoidal WBV is believed to induce
various neural responses that may subsequently influence
force transmission (Lundstrom and Holmlund, 1998;
Seidel and Griffin, 1998). A vibrated muscle may
undergo an active contraction, which is known as the
tonic vibration reflex (Bosco et al., 1999b; Mester et al.,
1999). Vibrating a muscle may also depress the
excitability of motor neurons innervating the antagonist
muscles or suppress the monosynaptic stretch reflexes of
the vibrated muscles (Bishop, 1974). Recent work on
human postural control during leg vibration also indicates
that vibration modulates postural responses (i.e. body tilt,
leaning), thereby influencing the propagation of forces
throughout the body (Polonyova and Hlavacka, 2001;
Tjernstrom et al., 2002). Other factors may also
contribute to the transmission of vibratory-induced forces
(i.e. posture, gender and bodymass). Nonetheless, the
results of this study indicate that the greatest g-forces are
found in the lower leg with significant damping
occurring at the more superior sites. This in part explains
the injuries reported by Cronin et al. (unpublished data)
and the reason for pre-screening for conditions such as
acute inflammations, fractures, and acute tendinopathies
as recommended by the manufacturers of the Galileo
vibration machine.
It should be noted that collapsing data as per this
study and analysing the mean responses to vibratory
stimulation does in no manner give any indication of the
interaction between frequency, foot position posture and
body site nor individual responses. This study, as with
previous research, has indicated large variations in the
individual responses to WBV (Pope et al., 1996;
Lundstrom and Holmlund, 1998; Matsumoto and Griffin,
1998; Mansfield and Griffin, 2000). For example, the g-
forces experienced at the tibial tuberosity whilst squatting
(frequency, 30 Hz; amplitude, 1.25 mm; foot position 2)
was 6.98 for one subject whereas it was 2.17 for another.
Though some recommendations have been made in terms
of progressive overload based on the findings of this
study, it should be realized that individual responses to
WBV differ. With this in mind one must be careful in
prescribing vibratory stimulation based on the mean
response as some individuals may or may not be able to
tolerate such loading.
4.5. Implications for physical activity and health
4.5.1. Bone development
The application of WBV has been shown to positively
influence bone development (i.e. BMD, bone formation
rate) within various animal models (Rubin et al., 1995,
2001, 2002; Flieger et al., 1998; Judex et al., 2001, 2002)
and within humans (Rubin et al., 1998; Ward et al., 2001;
Pitukcheewanont et al., 2002). These studies are character-
ised by higher frequencies (30 90 Hz) but somewhat lower
g-forces (0.2–2g) than that observed in this study. Thus, the
g-forces observed under the various conditions in this study
(0.34 3.91g) appear to be of sufficient magnitude to
provide an effective stimulus for bone development.
However, the responsiveness of bone to vibratory stimu-
lation may be in some way constrained by the bone’s
stiffness, strength and architecture (Jiang et al., 1999). If a
stimulus ‘threshold’ exists then low magnitude loading may
be ineffective regardless of the number of cycles (fre-
quency) or exposure period. It may be that a combination of
these factors (i.e. magnitude, frequency) and the unusual
distribution of a vibratory stimulus that facilitates the
greatest osteogenic responses (Lanyon, 1992; Jiang et al.,
1999). The responsiveness of bone to mechanical stimuli
may also depend upon genetic variations. Judex et al. (2002)
found that subtle genotypic variation among mice had a
significant effect upon trabecular bone quality and quantity
after exposure to mechanical vibration. Extrapolating these
results to humans suggests that the response to vibration
loading may also be subject dependent. Considering the
complex nature of prescribing vibration and indeed the
complexity of the human response to vibration, establishing
the optimal dose-response relationship remains difficult.
4.5.2. Performance/health
Many studies have found WBV to positively influence
various performance measures such as strength, force
output, power output and vertical jump performance
(Bosco et al., 1998a,b, 1999c, 2000; Torvinen et al.,
2002a; Warman et al., 2002). These studies are character-
ised by similar frequencies (25 50 Hz) and amplitudes (1
10 mm and 3 7 g) to that used in this study. It is speculated
that the development of some of these qualities may further
improve the quality of movement and life in the injured or
aged. For example, improving muscular strength, co-
ordination and balance would reduce the risk of falling
and the risk of fractures in osteoporotic bones (Heinonen
et al., 1999; Runge et al., 2000). Two months of WBV
training (6 min exposure at 27 Hz, 714 mm) has been
shown to improve lower limb neuromuscular function as
demonstrated by the improved co-ordination and balance of
35 elderly subjects performing a standardised chair-rising
test (Runge et al., 2000). However, the majority of research
in this area has used athletes or trained subjects. As the
adaptations occurring within non-athletic or untrained
populations may differ considerably to that seen in trained
B. Crewther et al. / Physical Therapy in Sport 5 (2004) 37–43 41
populations, it is suggested that further research investigate
the adaptations and responses of these populations (i.e.
injured, aged) to WBV interventions. These studies should
also seek to establish safe and effective loading parameters
for these populations.
4.5.3. Ill effects
Chronic exposure to occupational vibration has many
side effects including vertigo, haemodynamic alterations,
low back pain and visual impairment (Seidel and Griffin,
1998; Mester et al., 1999). Although, sinusoidal WBV may
not induce these effects, 17 subjects from this study reported
some type of ill effect. Two subjects withdrew from the
study, one due to severe discomfort in the hip region and the
other due to severe head motion (i.e. excessive shaking).
The most common ill effects were hot feet ðn¼6Þand
itching in the lower limbs ðn¼5Þ:An increase in vibration
frequency and hence a higher rate of foot contacts, is the
likely explanation for the high temperatures reported at the
feet. Previous research has also reported itching in the lower
limbs after exposure to sinusoidal WBV (Pope et al., 1996;
Rittweger et al., 2000), though the mechanism for this
response remains unknown. Other reported effects include
nausea, cramp, calf pain and lower back discomfort. These
findings may be compounded by the fact that heels were
required to be in contact with the vibration surface.
Nonetheless, the effects reported in this study, as with
other research, have generally occurred at frequencies of
30 Hz and above. Thus, the application of WBV should be
used with caution at higher frequencies (.30 Hz), higher
amplitudes and hence higher g-forces, particularly among
populations more susceptible to injury (i.e. elderly,
untrained). It would also seem prudent to monitor the
duration of vibration exposure at higher frequencies
considering the effects reported in this study and the
exposure period at 30 Hz (,2 min).
6. Conclusion
The use of WBV as a tool for improving functional
performance (flexibility, strength, power, balance, etc.) and
health (improving bone density) remains an exciting area for
further study. However, the research within these areas is in
its infancy. Much research is still needed on the optimal
frequencies, amplitudes, g-forces and stimulation durations
to improve each of these factors. Furthermore, knowledge as
to how many sessions per day and/or per week as well as
when to progressively overload vibratory stimulation is
practically non-existent. The results of this study indicate
that altering the frequency and amplitude of WBV as well as
posture can significantly alter the resulting g-forces
throughout the body. However, it is still unknown how
best to determine when an individual is ready for an increase
in frequency or amplitude, and/or for a change in posture.
Biomechanical and/or biological markers need to be
determined that assist in decision making as to the correct
timing of the overload stimulus. Such an approach will
greatly assist in the safe and effective use of WBV as a
rehabilitation and training tool. With this in mind one
should remain cognizant of the limitations that exist in the
interpretation of the current research findings and the need
for further research in this field.
This study was supported by the Health Research Council
of New Zealand through the Auckland University of
Technology/Health Research Council Summer Studentship.
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... When transmissibility is higher >1, it is amplified by the body; when it is <1, the input vibration is damped by the system. Vibration transmissibility has been examined at various lower extremity structures such as, foot, ankle, knee, and hip, and other body parts such as the spine and head [9,[12][13][14]. At a knee angle of 152° and a vibration frequency of 33 Hz a transmission ratio of 2.0 (ankle), 0.6 (knee), 0.13 (hip), 0.1 (sternum), and 0.3 (head) [10] (Fig. 5.3) is revealed. ...
... At a knee angle of 152° and a vibration frequency of 33 Hz a transmission ratio of 2.0 (ankle), 0.6 (knee), 0.13 (hip), 0.1 (sternum), and 0.3 (head) [10] (Fig. 5.3) is revealed. Transmissibility is influenced by people's body composition [10,11], vibration frequency and amplitude [12,15,16], body posture [9,11,17,18], and the type of postural movement i.e., static or dynamic movement [19]. It has been suggested that a significant amplification of peak acceleration may occur at 10-40 Hz for the ankle, 10-25 Hz for the knee, 10-20 Hz for the hip, and 10 Hz for the spine [15]. ...
This biomechanistic approach of vibration exercise discusses the human body as a group of segments (foot, shank, thigh, trunk, head) balanced on top of each other. These segments are interlinked by joints, the stiffness of which is generated by the surrounding muscles. Reflexes and pre-tension of the muscles are important factors that modulate the apparent joint stiffness and leg stiffness. In addition, leg stiffness is also affected by posture, with greater leg stiffness occurring in erect posture than in a crouched posture.
... The measures are stated in terms of force-motion relation, apparent mass, absorbed power, mechanical impedance and flow of vibration through human subject i.e seat to head (STHT) vibration transmissibility. There are number of researchers who perform research in this area, Crewther et al. [1] determines the gravitational forces at different body postures and also at different amplitudes, frequencies and anatomical sites. This study, collapses whole data into four different categories (posture, frequency, damping and amplitude) and find the gravitational forces in each category. ...
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Whenever a human body stands on a platform like a bus, train, etc then the waveform, frequency, amplitude, and duration due to vibrations can be changing and these variations produce some advantages in muscles and bone mineral density whereas high acceleration of platform viewed as dangerous. The reason behind this is the resonance of the human body that depends upon some factors: the seat surface material, the posture, vibration magnitude, and frequency, etc. In this study, modal and harmonic response analysis has been performed to calculate the natural frequencies of Indian human male subjects in standing posture conditions under un-damped and damped free vibration conditions. With the help of this, we are capable to know how these vibrations affect our muscles, bones, joints, etc. Joint studies of the human body help us to replace body joints in case of any serious injury or in emergency and multibody dynamics, modal analysis, and harmonic response play crucial roles in these effects. This study shows the vibration effects of transmissibility and stresses on the knee joints and neck joints of the human body. For this purpose, a revolute joint is separately designed and fixed at the location of joints in human subjects to understand the effect of these vibrations. The results are determined in this study are within the frequency range of 0-20 Hz.
... This greater muscle activation generated by rotational WBV can result in increased isometric activity of the musculature [54]. Likewise, it has been shown that accelerations in the ankle are greater during rotational WBV [55,56]. This greater mechanical load on the ankle produced with rotational WBV can further activate the musculature at this level, especially the anterior tibial, whose neural excitability is highly associated with mediolateral oscillation [57] and gastrocnemius [53,58]. ...
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Whole body vibration has been proven to improve the health status of patients with fibromyalgia, providing an activation of the neuromuscular spindles, which are responsible for muscle contraction. The present study aimed to compare the effectiveness of two types of whole body vibrating platforms (vertical and rotational) during a 12-week training program. Sixty fibromyalgia patients (90% were women) were randomly assigned to one of the following groups: group A (n = 20), who performed the vibration training with a vertical platform; group B (n = 20), who did rotational platform training; or a control group C (n = 20), who did not do any training. Sensitivity measures (pressure pain and vibration thresholds), quality of life (Quality of Life Index), motor function tasks (Berg Scale, six-minute walking test, isometric back muscle strength), and static and dynamic balance (Romberg test and gait analysis) were assessed before, immediately after, and three months after the therapy program. Although both types of vibration appeared to have beneficial effects with respect to the control group, the training was more effective with the rotational than with vertical platform in some parameters, such as vibration thresholds (p < 0.001), motor function tasks (p < 0.001), mediolateral sway (p < 0.001), and gait speed (p < 0.05). Nevertheless, improvements disappeared in the follow-up in both types of vibration. Our study points out greater benefits with the use of rotational rather than vertical whole body vibration. The use of the rotational modality is recommended in the standard therapy program for patients with fibromyalgia. Due to the fact that the positive effects of both types of vibration disappeared during the follow-up, continuous or intermittent use is recommended.
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This study evaluated the serum cortisol response to a single session of whole-body vibration (WBV) in healthy adult dogs. Ten healthy adult medium dogs, females and males, aged between 24 and 48 months and with body weight between 10.1 and 17.9 kg were used. A single WBV session at a frequency of 30 Hz for 5 min (3.10 mm peak displacement, 11.16 m/s2 peak acceleration, and 0.29 m/s velocity), then 50 Hz for 5 min (3.98 mm peak displacement, 39.75 m/s2 peak acceleration, and 0.62 m/s velocity), and finishing with 30 Hz for 5 min (3.10 mm peak displacement, 11.16 m/s2 peak acceleration, and 0.29 m/s velocity) was performed. Serum cortisol, heart and respiratory rate, and systolic blood pressure were evaluated at different time points: 1 min before WBV (1PRE) and 1 min (1POST), 60 min (60POST), and 360 min (360POST) after the WBV session. An increase (P = 0.0417) of the serum cortisol values was observed between 1PRE and 1POST and a decrease (P = 0.0417) between 1POST and 60POST and between 60POST and 360POST. However, the values remained within the reference range. The heart and respiratory rate and the systolic blood pressure remained unchanged. Our findings suggest that a single bout of WBV (5 min of 30 and 50 Hz) using a vibrating platform that delivered a vortex wave circulation does not modify the serum cortisol levels and clinical parameters of healthy adult dogs.
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Background: Whole-Body Vibration (WBV) consists of mechanical vibration stimuli produced that propagate throughout the body by increasing the gravitational load. The WBV can increase muscle mass in dogs with muscular atrophy. As Whole-body vibration (WBV) can be used as exercise modality with no impact on the joints, the present study aimed to evaluate the effects of single session of WBV in hematobiochemical and hemogasometric parameters in adult and elderly healthy dogs. Materials, Methods & Results: Fourteen clinically healthy, neutered crossbreed male dogs, non-athlete were selected. The dogs were divided into two groups of seven dogs, according to the age group: Group I - adult dogs (GI): age between 12.0 and 84.0 months old; Group II - elderly dogs (GII): age above 84.0 months old. All dogs were submitted to a single session WBV by using a vibrating platform that delivered a vortex wave circulation as mechanical vibration. The WBV protocol used was 30 Hz frequency (3.10 mm peak displacement; 11.16 m/s2 peak acceleration; 0.29 m/s velocity), then 50 Hz (3.98 mm peak displacement; 39.75 m/s2 peak acceleration; 0.62 m/s velocity), and lastly 30 Hz (3.10 mm peak displacement; 11.16 m/s2 peak acceleration; 0.29 m/s velocity) for 5-min between de frequencies. The hematobiochemical and hemagasometric parameters were evaluated at 1-min before the WBV session (1PRE), 1-min after the WBV session (1POST), 120-min (120POST) and 24 hours after the WBV session (24hPOST). The dogs accepted well the vibration stimulus, however, elderly dogs weighting above 30 kg were more likely to sit down with increased frequency from 30 to 50 Hz. No variations of food and water intakes and gastrointestinal changes were observed after the WBV session. Hemoglobin values showed significant decrease (P = 0.0312) between 1PRE and 1POST in elderly dogs. A significant decrease (P = 0.0453) was observed in alanine aminotransferase values between 120POST and 14hPOST in adult dogs. Creatinine values had a statically decrease (P = 0.0173) between 1PRE and 24hPOST in adult dogs. However, these values remained within the reference range for dogs. Discussion: According to the literature, there are no studies related to the effects of WBV in haematobiochemical and hemogasometric parameters in adult and elderly dogs. No deleterious effects regarding to a single session of WBV were observed, however harmful effects were observed in human patients. The elderly dogs with body mass above 30 kg tried to sit during the increased frequency from 30 to 50 Hz, which was associated with the pressure exerted in their paws. No significant differences were observed in erythrogram and leukogram parameters except for hemoglobin values. Significant decline was observed in hemoglobin values in adult Beagle dogs; and were associated with hemolysis. The significant decrease in alanine aminotransferase and creatinine values did not have clinical significance. No significant alterations were identified in hemogasometric parameters but slight increase in pH values was observed in horses subjected to a 60 km run, and was associated to the loss of Cl ions in sweat. The single session of WBV by using a vibrating platform that delivered a vortex wave circulation, at 30 and 50 Hz frequencies for 5 min did not induced significant changes in hematobiochemical and hemogasometric parameters in adults and elderly healthy dogs.
Background Whole-body vibration (WBV) has emerged as a potential intervention paradigm for improving motor function and bone growth in children with disabilities. However, most evidence comes from adult studies. It is critical to understand the mechanisms of children with and without disabilities responding to different WBV conditions. This study aimed to systematically investigate the acute biomechanical and neuromuscular response in typically developing children aged 6–11 years to varying WBV frequencies and amplitudes. Methods Seventeen subjects participated in this study (mean age 8.7 years, 10 M/7F). A total of six side-alternating WBV conditions combining three frequencies (20, 25, and 30 Hz) and two amplitudes (1 and 2 mm) were randomly presented for one minute. We estimated transmission of vertical acceleration across body segments during WBV as the average rectified acceleration of motion capture markers, as well as lower-body muscle activation using electromyography. Following WBV, subjects performed countermovement jumps to assess neuromuscular facilitation. Findings Vertical acceleration decreased from the ankle to the head across all conditions, with the greatest damping occurring from the ankle to the knee. Acceleration transmission was lower at the high amplitude than at the low amplitude across body segments, and the knee decreased acceleration transmission with increasing frequency. In addition, muscle activation generally increased with frequency during WBV. There were no changes in jump height or muscle activation following WBV. Interpretation WBV is most likely a safe intervention paradigm for typically developing children. Appropriate WBV intervention design for children with and without disabilities should consider WBV frequency and amplitude.
The aim of this study was to evaluate the effects of a single-session of whole-body vibration (WBV) exercise on haematological and serum biochemical parameters and serum cortisol levels in healthy adult cats. Ten healthy neutered crossbred cats, five males and five females, aged 2 to 4 years and weighing 3.25-5.15 kg, were enrolled. All cats were tested in the same period starting at 12:00 a.m. and under same environmental conditions. A 1 h period of acclimatisation and rest was completed prior to the WBV session. During the WBV session, the cat was placed in a standing position on the centre of the vibrating platform. Each cat was exposed to a single WBV session. The protocol was 30 Hz for 5 min, followed by 50 Hz for 5 min and finishing with 30 Hz for 5 min. The peak displacements were 3.10 mm and 3.98 mm and the peak accelerations 55.0 m/s and 195.96 m/s. Complete blood cell count, serum biochemistry (alanine aminotransferase, creatinine, creatine phosphokinase) and serum cortisol were determined at three time-points: before (T0), immediately after (T1), and at 4 h after the end of the WBV session (T2). Immediately after increasing the frequency from 30 to 50 Hz, two cats (20%) tried to sit and showed signs of agitation that ceased after 15 s. No cat tried to jump out. The variables presented no statistically significant differences among the time-points. In conclusion, a 15 min session of WBV exercise at frequencies of 30, 50 and 30 Hz does not cause significant changes in haematological or serum biochemical parameters, nor in serum cortisol levels in healthy adult cats.
This chapter describes a new method for pinpointing the latency of the vibration-induced muscular reflex. To determine the reflex latency, the vibration-altered electromyography (EMG) and acceleration data were spike triggered and averaged using the tip of the EMG response as the trigger. Averaged results belonging to several different vibration frequencies were then superimposed to achieve a ‘cumulative averaged record’. The lowest standard error of the cumulative averaged record for the acceleration data was marked to indicate the effective stimulus point on the vibration cycle. Similarly, the lowest standard error of the cumulative averaged record for the EMG data showed the start of the reflex response. The time between the effective stimulus point and the start of the reflex response on EMG data was designated as the ‘reflex latency’ of this circuit. Using this technique, we have examined the latency of whole-body vibration (WBV)-induced reflexes. We found that the WBV induced two different reflex responses depending on the vibration amplitude. While low amplitude WBV (0.1–0.4 mm) produced short latency reflex similar to muscle spindle-based T-reflex (34 ms), high amplitude vibration (1.1–2.8 mm) generated long latency reflex response (44 ms) which may have a different receptor origin than the spindles. We have also summarized the modulatory effects of vibration on spindle-based reflexes and indicated that these reflexes are reduced during and/or following vibration. It is suggested that this effect may originate from the reduction in effectiveness of the spindle synapses on motoneurons via premotoneuronal means.
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Purpose: This randomized controlled study was designed to investigate the effects of a 4-month whole body vibration-intervention on muscle performance and body balance in young, healthy, nonathletic adults. Methods: Fifty-six volunteers (21 men and 35 women, aged 19-38 yr) were randomized to either the vibration group or control group. The vibration-intervention consisted of a 4-month whole body vibration training (4 min?d(sup-1), 3-5 times a week) employed by standing on a vertically vibrating platform. Five performance tests (vertical jump, isometric extension strength of the lower extremities, grip strength, shuttle run, and postural sway on a stability platform) were performed initially and at 2 and 4 months. Results: Four-month vibration intervention induced an 8.5% (95% CI, 3.7-13.5%, P = 0.001) net improvement in the jump height. Lower-limb extension strength increased after the 2-month vibration-intervention resulting in a 3.7% (95% CI, 0.3-7.2%, P = 0.034) net benefit for the vibration. This benefit, however, diminished by the end of the 4-month intervention. In the grip strength, shuttle run, or balance tests, the vibration-intervention showed no effect. Conclusion: The 4-month whole body vibration-intervention enhanced jumping power in young adults, suggesting neuromuscular adaptation to the vibration stimulus. On the other hand, the vibration-intervention showed no effect on dynamic or static balance of the subjects. Future studies should focus on comparing the performance-enhancing effects of a whole body vibration to those of conventional resistance training and, as a broader objective, on investigating the possible effects of vibration on structure and strength of bones, and perhaps, incidence of falls of elderly people.
Vibratory stimulation of skeletal muscle produces reflex effects which promise to become useful in the evaluation and treatment of motor disorders. This paper reviews results of numerous studies in which responses of normal muscles to vibratory stimulation have been analyzed. Vibration, by exciting selectively the primary endings of muscle spindles, evokes asynchronous, slowly augmenting activity in the vibrated muscle known as the tonic vibration reflex or TVR. Although a stretch reflex and the TVR share the same afferent fibers, the TVR requires support from supraspinal regions of the central nervous system (CNS). Normal individuals can voluntarily inhibit or augment a TVR. Among factors influencing the strength of a TVR are the position of the vibrator, the initial length of the muscle, CNS excitability, and the frequency and amplitude of the vibratory stimulus. The neural mechanisms by which these factors exert their effects are discussed.
The effects of whole body vibrations on the mechanical behaviour of human skeletal muscles were studied in 14 physically active subjects randomly assigned to the experimental (E) or control (C) group. Group E was subjected to 5 sets of vertical sinusoidal vibrations lasting up to 2 min each, for 10 min daily, for a period of 10 days. The control subjects were requested to maintain their normal activity and to avoid strength or jumping training. The subjects were tested at the beginning and at the end of the treatment. The test consisted of specific jumping on a resistive platform. Marked, significant improvements were noted in Group E in the power output and height of the best jump (by 6.1 and 12%, respectively, P<0.05) and mean jump height in continuous jumping for 5 s (by 12%, P<0.01). In contrast, no significant variations were noted in Group C. It was suggested that the effect of whole body vibration elicited a fast biological adaptation associated with neural potentiation.
INTRODUCTION The current tenet of mechanically related bone adaptation suggests that mechanical signals must be large in magnitude to stimulate bone formation. In contrast to this "bigger is better" perspective, recent studies have demonstrated the strong anabolic potential of extremely low magnitude -but high frequency -mechanical signals. Considering the osteogenic character of these high frequency mechanical stimuli, we hypothesize that introducing these signals will serve as an effective countermeasure for the bone loss which parallels disuse. Importantly, these low level signals may play a critical role in defining and maintaining normal bone mass and morphology, as they persist over long durations, including passive actions such as standing, and therefore represent a dominant component of bone's functional strain history. Not surprisingly, therefore, conditions such as microgravity (or a model of this pathology such as rat-tail suspension) may abolish this key regulatory stimulus, and thus permit resorptive activity. In an effort to "reintroduce" these low-level mechanical stimuli, we have devised a prototype, categorized as "non-significant risk" by the FDA, which can increase bone formation by inducing extremely low level mechanical stimuli into the lower appendicular and axial skeleton. Importantly, this unique biomechanical intervention affords the ability to examine the molecular basis of an osteogenic signal, thus identifying novel targets for drug development. Osteoclast differentiation factor (ODF) is a cytokine involved the recruitment and activity of osteoclasts and in vitro studies have linked its upregulation to the absence of mechanical strain. Here, we first examined the osteogenic efficacy of low-level high frequency mechanical stimuli and their ability to reverse the bone loss which arises under microgravity. We then hypothesized that the expression of ODF would be inversely related to altered tissue level bone formation rates. METHODS Female 6 months old Sprague-Dawley rats were assigned to controls (n=30), mechanically stimulated (n=21), tail suspension related disuse (n=11), disuse interrupted by 10min/d of normal weight bearing (n=7), and disuse interrupted by 10min/d of 90Hz stimulation at 0.25g (n=19). All experimental procedures were applied for 28d. Mechanical stimulation consisted of whole body vibration at 90Hz (0.25g). All rats were given injections with demeclocycline prior to the beginning of the study and calcein on day 18 of the protocol to determine histomorphometric indices of bone formation. ODF mRNA levels were quantitated in three animals of each group (except disuse + weight bearing group) via Northerns. RNA was extracted from whole left tibiae, including bone marrow and cartilage. RESULTS Body mass of the rats did not change significantly in any of the groups during the course of the 28d study. Mechanical stimulation at 90Hz for 10 min/d proved to be a strong osteogenic stimulus as indicated by increased trabecular bone formation rates (+97%, Fig. 1a). Hindlimb suspension significantly decreased trabecular bone formation rates by 92% as compared to controls. This suppression was not significantly different from the animals subject to disuse for most of the day (23h, 50min) and then allowed to freely bear weight for 10 min/d (D+WB). In contrast, when low-level mechanical stimulation was applied for 10min/d to combat disuse, the countermeasure served to normalize bone formation rates back to control values.
Study Design. A randomized controlled trial with a 6-month follow-up period was conducted. Objective. To compare lumbar extension exercise and whole-body vibration exercise for chronic lower back pain. Summary of Background Data. Chronic lower back pain involves muscular as well as connective and neural systems. Different types of physiotherapy are applied for its treatment. Industrial vibration is regarded as a risk factor. Recently, vibration exercise has been developed as a new type of physiotherapy. It is thought to activate muscles via reflexes. Methods. In this study, 60 patients with chronic lower back pain devoid of "specific" spine diseases, who had a mean age of 51.7 years and a pain history of 13.1 years, practiced either isodynamic lumbar extension or vibra- tion exercise for 3 months. Outcome measures were lum- bar extension torque, pain sensation (visual analog scale), and pain-related disability (pain disability index). Results. A significant and comparable reduction in pain sensation and pain-related disability was observed in both groups. Lumbar extension torque increased sig- nificantly in the vibration exercise group (30.1 Nm/kg), but significantly more in the lumbar extension group (59.2 Nm/kg; SEM 10.2; P 0.05). No correlation was found between gain in lumbar torque and pain relief or pain- related disability (P 0.2). Conclusions. The current data indicate that poor lum- bar muscle force probably is not the exclusive cause of chronic lower back pain. Different types of exercise ther- apy tend to yield comparable results. Interestingly, well- controlled vibration may be the cure rather than the cause
The influence of the posture of the legs and the vibration magnitude on the dynamic response of the standing human body exposed to vertical whole-body vibration has been investigated. Motions were measured on the body surface at the first and eighth thoracic and fourth lumbar vertebrae (T1, T8 and L4), at the right and left iliac crests and at the knee. Twelve subjects took part in the experiment with three leg postures (normal, legs bent and one leg), and five magnitudes of random vibration (0·125–2·0 ms−2r.m.s.) in the frequency range from 0[msde]5–30 Hz. The main resonance frequencies of the apparent masses at 1·0 ms−2r.m.s. differed between postures: 5·5 Hz in the normal posture, 2·75 Hz in the legs bent posture and 3·75 Hz in the one leg posture. In the normal posture, the transmissibilities to L4 and the iliac crests showed a similar trend to the apparent mass at low frequencies. With the legs straight, no resonance was observed in the legs at frequencies below 15 Hz. In the legs bent posture, a bending motion of the legs at the knee and a pitching or bending motion of the upper-body appeared to contribute to the resonance of the whole body as observed in the apparent mass, with attenuation of vibration transmission to the upper body at high frequencies. In the one leg posture, coupled rotational motion of the whole upper-body about the hip joint may have contributed to the resonance observed in the apparent mass at low frequencies and the attenuation of vertical vibration transmission at high frequencies. The resonance frequency of the apparent mass in the normal posture decreased from 6·75–5·25 Hz with increasing vibration magnitude from 0·125 to 2·0 ms−2r.m.s. This “softening” effect was also found in the transmissibilities to many parts of the body that showed resonances.
Low bone density (BD) in adolescence is a predictor for osteoporosis later in life. Although pharmaceutical regimes are available to inhibit bone loss in adults, safe, effective means of improving BD in children have yet to be defined. Short-term, low-intensity, high-frequency mechanical stimulation has improved BD and bone strength in animal models of osteoporosis. To determine the effect of this mechanical signal on children, a pilot study of 8 female subjects (mean age standard deviation [SDI = 9.7 +/- 1.5 years) was performed. All but one subject had BD > 1 SD below normal. Over 8 weeks, subjects stood for 30 minutes, 3 times/week, vibrating at 30 Hz at 0.3 g. Blood for bone-specific alkaline phosphatase (BALP) and quantitative computed tomography (CT) measurements of the lumbar spine and femurs were obtained at baseline and 8 weeks. Cancellous BD of the spine and cortical BD, fat mass, muscle mass, and cortical bone area (CBA) of the femurs were evaluated. After treatment, there was a significant increase of 6.2% in cancellous BD, 2.1% in cortical BD, and 6.1% in muscle mass. Mean BALP levels increased by 16.6%. No significant differences were found in fat mass or CBA. These results indicate that mechanical intervention may be an effective means of significantly increasing BD in children with low BD as well as increasing muscle mass at the femurs.