Showing papers by "Serge S. Colson published in 2013"

Time Course of the Cross-Over Effect of Fatigue on the Contralateral Muscle after Unilateral Exercise

Abstract: We investigated the cross-over effect of muscle fatigue and its time course on the non-exercising contralateral limb (NEL) after unilateral fatiguing contractions of the ipsilateral exercising limb (EL). For this purpose, 15 males performed two bouts of 100-second maximal isometric knee extensions with the exercising limb, and neuromuscular function of both the EL and NEL was assessed before (PRE), after a first fatiguing exercise (MID) and after a second fatiguing exercise (POST). Maximal voluntary isometric torque production declined in the EL after the first bout of exercise (−9.6%; p<0.001) while in the NEL, the decrease occurred after the second bout of exercise (−10.6%; p<0.001). At MID, torque decline of the EL was strictly associated to an alteration of the mechanical twitch properties evoked by neurostimulation of the femoral nerve (i.e., peak twitch torque, maximal rate of twitch development). According to these markers, we suggest that peripheral fatigue occurred. At POST, after the second bout of exercise, the voluntary activation level of the knee extensor muscles was altered from PRE (−9.1%; p<0.001), indicating an overall central failure in both the EL and NEL. These findings indicate that two bouts of unilateral fatiguing exercise were needed to induce a cross-over effect of muscle fatigue on the non-exercising contralateral limb. Differential adjustments of the motor pathway (peripheral fatigue vs. central fatigue) might contribute to the respective torque decline in the EL and the NEL. Given that our unilateral fatiguing exercise induced immediate maximal torque reduction in the EL and postponed the loss of torque production in the NEL, it is also concluded that the time course of muscle fatigue differed between limbs.

What is contained in the excessive spikes in sEMG spectrum during whole‐body vibration: motion artifacts or stretch reflexes ?

Abstract: Whole-body vibration (WBV) has been shown to result in augmented muscle activity during the exposure to the vibration, which has been assessed with surface electromyography (sEMG). While numerous studies have focused on the evaluation of the optimal training parameters using sEMG recordings during WBV, its validity is still debated. Briefly, excessive peaks at the vibration frequency and its multiple harmonics are displayed in the sEMG frequency spectrum. Unfortunately, only a few studies have addressed this issue, and to date it is not clear whether the spikes observed in the frequency domain during WBV arise from stretch reflexes (Ritzmann et al., 2010), motion artifacts (Fratini et al., 2009), or both (Sebik et al., 2012). Therefore, the aim of this study was to gain insight about the origin of these excessive peaks by analyzing sEMG signals from muscles and signals from dummy electrodes placed on the patella. It was hypothesized that (1) motion artifacts are observed in the patella signal at the vibration frequency and its multiple harmonics during WBV, and that (2) the sEMG of the spikes is linearly related to the sEMG without the spikes.