vibration (WBV) has been suggested to be particularly effective
on the stretch-shortening cycle-based movements, such as the counter
movement jump (CMJ) test (Issurin, 2005).
Nevertheless, the literature on short-term vibration exposure and
lower limb explosive performance (measured by CMJ test) is contradictory.
Either transient improvements (Bosco et al., 2000;
Cochrane and Stannard, 2005;
Torvinen et al., 2002a)
or no effects (Torvinen et al., 2002b;
Rittweger et al., 2003;
Cormie et al., 2006)
have been reported after a single WBV exposure ranging from 30 s
to 10 min. The present study aimed at better characterizing the
use of a single short bout of WBV as a mode of warming up before
a CMJ test.
A total of 114 university students (37 men, 77 women, aged 19.6
± 2.0 years) signed an informed consent form and volunteered to
participate in the study. The study protocol was approved by the
Review Committee for Research Involving Human Subjects of our center.
Participants were asked to come to the laboratory in three occasions
three days apart. First visit: familiarization session aiming to
learn the CMJ technique and to experience the vibration stimulus.
Second visit: the participants performed three consecutive CMJ with
one min rest interval. No significant differences were observed
among the jumps, and the highest score was retained. Third visit:
the participants were exposed to a single short bout of WBV and
immediately after they performed three CMJ with one min rest interval.
An infrared contact timing platform (ERGO JUMP Plus - BOSCO SYSTEM,
Byomedic, S.C.P., Barcelona, Spain) was used to measure "flight"
time (t) during the vertical jump (accuracy 0.001 s). Maximum height
achieved by the body centre of gravity (h) was then estimated, i.e.
h = g · t2 / 8, where g = 9.81 m/s2. In all occasions, the participants
were instructed to abstain from strenuous exercise for the preceding
Whole-body vibration was carried out on an oscillating vibrating
platform (Galileo 900, Novotec, Pforzheim, Germany). Since a suitable
protocol of WBV has not been definitely established (Cormie et al.,
participants were randomly allocated into five groups with different
vibration protocols. The proportion of males (from 30.8 to 36.8
%) was similar in the five groups. Vibration amplitude was fixed
at ± 3 mm (i.e., peak-to-peak of 6 mm) for all groups, while frequency
and duration ranged from 20 to 30 Hz and 90 or 120 s, respectively
(Table 1). The time over the
platform was equally distributed in three positions: 1st) isometric
squat at a knee angle of approximately 120º, standing on the toes;
2nd) isometric squat at a knee angle of approximately 120º, standing
on the whole foot; and 3rd) dynamic half squats (lower limit: 90º
knee angle) at a fixed rhythm marked by a metronome (2.4 s per squat).
Sport shoes were required during the entire vibration stimulus and
all CMJ tests.
The interaction between sex, WBV protocol- group and CMJ performance
was analysed by means of two-way repeated measures analysis of the
variance (ANOVA). Since no significant interaction was found, males
and females, as well as the five groups were analyzed together by
repeated measured analysis of covariance (ANCOVA), with sex and
WBV protocol-group as covariates. All the residuals showed a satisfactory
pattern. Pairwise comparisons were performed with Bonferroni adjustment.
The analysis was performed using the SPSS software v 15.0.1., and
the level of significance was set at 5%.
The CMJ performance significantly decreased immediately after WBV
was applied (p < 0.001). This decrease did not differ among the
five WBV protocols used, and ranged between 1.1 cm for the 20 Hz
- 90 s group and 2.7 cm for the 20 Hz - 120 s group. In the jumps
performed one and two min after WBV, the performance was recovered
up to the level achieved in the absence of WBV. Since the effect
of the five different WBV protocols on CMJ performance did not significantly
differ, the results are presented jointly (Figure
Reports concerning acute effects of WBV on jump performance yield
conflicting results. Transient benefits of 2.5, 4 and 8 % in CMJ
height has been reported after 4 min (Torvinen et al., 2002a),
10 min (Bosco et al., 2000)
and 5 min (Cochrane and Stannard, 2005)
of WBV stimulus,
respectively. The lack of improvement in our study may be partially
explained by the time elapsed between the vibration stimulus and
the jump test, since our subjects performed the CMJ immediately
after the WBV exposure. The different training level of the participants
may also explain discrepancies among studies, as our subjects were
not engaged in any regular exercise practice. It has been reported
that elite athletes may obtain more benefits from WBV than amateur
athletes do (Issurin and Tenenbaum, 1999).
In agreement with our results, other studies did not show improvement
on CMJ performance after a single bout of WBV (Cormie et al., 2006;
Rittweger et al., 2003;
Torvinen et al., 2002b).
Compared with our results, Cormie et al., 2006
did not find an impairment of CMJ performance immediately after
a single WBV bout of 30 s, which may be associated with their shorter
WBV stimulus (30 s), the interval actually elapsed between WBV and
CMJ test, and the higher training level of their participants.
In summary, whole-body vibration combined with voluntary contractions
does not seem to be a useful method for warming up before activities
involving vertical jumps. At least one minute interval recovery
should be allowed when using WBV in a range of 20-30 Hz and 90 or
120 s if maximal jump performance is required.
This study was conducted without any conflict of interest, without
financial assistance, and supported by grants from the Consejo Superior
de Deportes (109/UPB31/03, 13/UPB20/04), the Spanish Ministry of
Education and Science (AP2003-2128, AP-2004-2745; AP2005-3827; AP2005-4358)
and the HELENA study (European Community Sixth RTD Framework Programme,
FOOD-CT-2005-007034). We also acknowledge Maria T. Miranda (Biostatistics
Department, University of Granada) for her help with the statistics.