Effects of prolonged tendon vibration stimulation on eccentric and concentric maximal torque and EMGs of the knee extensors

the purpose of present study was to compare the effect of iaafferent attenuation on the activity of alpha motor neuron (mn)during concentric and eccentric action. eight male subjects wereenrolled in the present study. the experiments consisted of twosessions of mvc measurements, since all subjects performedboth maximal concentric and eccentric action. emg signalswere simultaneously measured. to establish the baseline ofstrength, subjects were asked to perform mvc of knee extensionin each session. after finishing the measurements, 20 minof vibration stimulation was applied. immediately after finishingvibration stimulation, the mvc and aemg were again measured.the means of mvc for concentric knee extension at preand post-vibration stimulation were 192.2 ± 49.3 nm and 162.3± 47.9 nm, respectively. the means of mvc for eccentric kneeextension at pre and post-vibration stimulation were 299.7 ±77.0 nm and 247.3 ± 88.6 nm, respectively. two-factor repeatedanova 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 interactioneffect (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 inaemg (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) andaction (f(1,7)=12.40, p = 0.0097) were noted in the vl and thevm 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 ofthe vl in response to the prolonged vibration stimulation weresignificantly reduced in eccentric contraction over concentriccontraction. these results represented that a deactivation effecton the alpha mn of the vl during eccentric action was greaterthan that of concentric action.