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Whether a whole body vibration session can enhance muscle voluntary activation remains debated. This pilot study thus investigated the acute effects of an intervention with whole body vibration versus a "sham" intervention on the voluntary activation of knee extensor muscles. Ten healthy subjects volunteered to participate in two interventions, vibration and sham, in randomized order. Knee extensor muscle voluntary activation, contractile properties and maximal voluntary isometric contraction were assessed before and immediately after each intervention. No significant differences were found for any of the variables. After both interventions, muscle activation remained unchanged, whereas maximal voluntary isometric contraction was significantly reduced (p<0.05). In conclusion, the two interventions induced the same adaptations in the knee extensors. These findings can be useful in conceiving whole body vibration protocols, although future research is warranted to address the influence of vibration on neural adaptation. [ABSTRACT FROM AUTHOR]

This study examined the impact of sport specificity on the time course of fatigue during maximal voluntary eccentric, concentric and isometric torque production following a submaximal isokinetic fatiguing exercise. Seven cyclists and seven triathletes performed a fatiguing exercise consisting of nine sets of 31 isokinetic concentric knee extensions at 1.05 rad·s-1. Fatigue was assessed pre-exercise, after three and six sets, and post-exercise. The maximal knee extension torque associated with electromyographic (EMG) activity was recorded during voluntary contractions and electrically induced contractions (single and paired twitches). The maximal voluntary eccentric torque production declined in cyclists (18 ± 3.5%, p <0.05) and was not significantly affected in triathletes (5 ± 2.5%, p >0.05). The decrease in cyclists was associated with an increase in the sum of the normalized EMG (nRMS) values of the three agonist muscles (p<0.01). Although no significant difference was observed between groups, the two-way repeated-measure analysis of variance revealed a time effect on maximal concentric and isometric torque, twitch contractile and electrophysiological response (Mmax) properties. No modification in the activation and coactivation levels was observed. In conclusion, these results indicate that the time course of fatigue, especially during eccentric contractions, is mediated by sport-specific adaptations likely due to the mode of muscle contraction used in the activity. [ABSTRACT FROM AUTHOR]