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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
Abstract
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.
doi:10.1016/j.ptsp.2003.11.004
Physical Therapy in Sport 5 (2004) 37–43
www.elsevier.com/locate/yptsp
*Corresponding author. Tel.: þ649-917-9999x7119; fax: þ649-917-
9960.
E-mail address: blair.crewther@aut.ac.nz (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
0.25–2g.
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
conducted.
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 (9.67–9.74g). 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
a
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
a
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
a
¼0:050
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
a
1.76
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
a
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
a
2.20
b
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
a
Significantly greater than position 2 ðP,0:05Þ:
b
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
a
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
a
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
a
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
g-forces.
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
WBV.
Table 5
Gravitational forces associated with different body positions
Jaw Greater trochanter Tibial tuberosity
Mean (g-force) 0.34 1.26
a
3.91
b
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
a
Significantly greater than the jaw ðP,0:05Þ:
b
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, 7–14 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.
Acknowledgements
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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