Antropomotoryka nr 55.indb - Akademia Wychowania Fizycznego w ...

B.P. Couto, S.A. Rodrigues, R.S. Ribeiro, M.D.M. Drummond, B.M.R. Rocha, L.A. Szmuchrowski
results corroborate the findings from several studies
that have also found positive results when applying
mechanical vibrations to vertical jumps [21, 24, 18, 20].
This increase in the height of vertical jumps may be
explained by the recruitment of motoric units of higher
thresholds that occurs during a vibration training [31].
Exercises with vibrations directly affect fast contraction
fibers that are determinants for the performance of vertical
jumps [22]. Additionally, an increase in the sensitivity
of muscle spindles generated by vibration training
[15] could increase the response of these proprioceptors
during the cycle of stretching and shortening that
occurs with a CMJ.
Other authors have used the vertical jump to identify
the force difference among contralateral limbs.
Newton, Gerber, Nimphius, Shim, Doan, Robertson
et al. [4] and Impellizzeri, Rampinini, Maffiuletti and
Marcora [6] identified force differences among contralateral
limbs, being 6.1% and 6.2% respectively. Ball and
Scurr [10] converted force data from Newton to body
weight (BW) to allow direct comparisons between participants,
and its results showed no difference of force
among contralateral limbs, with average of 4.7 BW
for both sides. McElveen, Riemann and Davies [9] did
not identify force difference among contralateral limbs.
At the present study significant force difference among
contralateral limbs were identified in all groups.
Unlike most of the articles that collected only force
data [10, 6, 4], it was decided to use force and impulse
data, as well as the study of McElveen, Riemann and
Davies [9], due to major importance of impulse in jumping
performance. According to Winter and Fowler [25],
impulse is fundamental to exercise, especially when
projectiles are involved. These projectiles could be implements
such as shot, javelin, and discus or the body in
horizontal and vertical jumping. In many circumstances,
it is optimization of the product of force and time that is
critical for success and which determines the limits of
performance. Impulse is determined mathematically by
the integral of the force-time curve and is what determines
the change of momentum of a body [26]. Thus, it
is possible that a higher force value produces lower
height jump, as a result of a short period of application of
this force, thus generating a smaller impulse. McElveen,
Riemann and Davies [9] did not identify force difference
among contralateral limbs but found impulse difference
among contralateral limbs (1,9%). As McElveen,
Riemann and Davies [9], in the present study was identified
impulse difference among contralateral limbs in all
groups. McBride, Kirby, Haines and Skinner [27] and
Ferreira, Schilling, Weiss, Fry and Chiu [28] also used
impulse as an important variable in jump height.
Lee and Carroll [13] admit that the unilateral strength
training is a possibility to reduce de force difference
among contralateral limbs. Another option would be bilateral
strength training but with the possibility of increasing
this difference among contralateral limbs, due to the probability
of voluntary greater use of the dominant limb [14].
Simon and Ferris [11] and Carson, Riek and Shahbazpour
[12] suggest the utilization of a feedback mechanism to
reduce the force difference among contralateral limbs,
so the volunteer try to produce the same amount of force
in both limbs. Although, it was observed that the subject
was able to match the force of his stronger limb to the
target force with visual feedback but was not able to accurately
produce equal forces among contralateral limbs.
Moreover, this practice can decrease the force difference
among contralateral limbs from the combination of
adequate stimulation of the non-dominant member with
reduced stimulation of the dominant member, and thus,
decrease the effects of training. It seems that strength
training associated with vibration training is an option to reduce
the force and impulse difference among contralateral
limbs, without decreasing the long-term training effects. It
can be demonstrated trough the different results obtained
between 8Hz and isometric groups, where only the group
submitted to this frequency of vibration obtained statistically
significant reduction of force and impulse difference
among contralateral limbs, without decreasing the longterm
improvements in the vertical jump performance.
An explanation for the decrease in force and impulse
difference among contralateral limbs in the training
done with vibrations should be related to short
periods of muscle-stretching added during the execution
of training. According to Rittweger [22], vibration
exercises should be characterized by cyclic transitions
between eccentric and concentric muscle contractions.
This sudden stretching could have optimized the action
of the muscle spindles, especially of the primary
endings of the spindle and the nervous stimulation rate
[21], once the stretching of the muscle spindles provoked
an increase in the frequency of the discharge of
the sensory endings. The vibration training might have
led to the results above mentioned due to reflex pathways
stimulation. This kind of application of mechanical
vibrations could have surpassed the voluntary limit of
strength production and contributed to the activation of
the involuntary components of muscle strength production
[19]. Thus, the dominancy by the volunteer would
be reduced.
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