چكيده لاتين :
The purpose of present study was to compare the effect of Ia
afferent attenuation on the activity of alpha motor neuron (MN)
during concentric and eccentric action. Eight male subjects were
enrolled in the present study. The experiments consisted of two
sessions of MVC measurements, since all subjects performed
both maximal concentric and eccentric action. EMG signals
were simultaneously measured. To establish the baseline of
strength, subjects were asked to perform MVC of knee extension
in each session. After finishing the measurements, 20 min
of vibration stimulation was applied. Immediately after finishing
vibration stimulation, the MVC and AEMG were again measured.
The means of MVC for concentric knee extension at pre
and post-vibration stimulation were 192.2 ± 49.3 Nm and 162.3
± 47.9 Nm, respectively. The means of MVC for eccentric knee
extension at pre and post-vibration stimulation were 299.7 ±
77.0 Nm and 247.3 ± 88.6 Nm, respectively. Two-factor repeated
ANOVA detected significant differences in the MVC.
Both main effects for pre-post condition (F(1,7)=, p = 0.0033)
and action (F(1,7)=26.35, p = 0.0013) were noted. No interaction
effect (action x condition) was noted. The means of AEMG
(vastus lateralis (VL), vastus medialis (VM), rectus femoris
(RF)) at pre and post -vibration stimulation were decreased.
Two-factor repeated ANOVA detected significant differences in
AEMG (VM and VL). Both main effects for pre-post condition
(VL;F(1,7)=7.27, p = 0.0308, VM; F(1,7)=9.55, p = 0.0175) and
action (F(1,7)=12.40, p = 0.0097) were noted in the VL and the
VM but not in the RF. Furthermore, significant interaction
(action x condition) effect was noted in the VM (F(1,7)=7.03, p
= 0.0328) but not in the VL. The MVC and the EMG activity of
the VL in response to the prolonged vibration stimulation were
significantly reduced in eccentric contraction over concentric
contraction. These results represented that a deactivation effect
on the alpha MN of the VL during eccentric action was greater
than that of concentric action.
