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Murviel-lès-Montpellier, France

Dupeyron A.,EA 2991 Motor Efficiency and Deficiency Laboratory | Perrey S.,EA 2991 Motor Efficiency and Deficiency Laboratory | Micallef J.-P.,EA 2991 Motor Efficiency and Deficiency Laboratory | Micallef J.-P.,French Institute of Health and Medical Research | Pelissier J.,EA 2991 Motor Efficiency and Deficiency Laboratory
Journal of Electromyography and Kinesiology | Year: 2010

There is still conflicting evidence about the influence of fatigue on trunk reflex activity. The aim of this study was to measure response latency and amplitude changes of lumbar and abdominal muscles after heavy external force perturbation applied to the trunk in the sagittal plane before and after back muscle fatigue, in expected and unexpected conditions. Ten healthy subjects in a semi-seated position, torso upright in a specific apparatus performed an intermittent back muscle fatigue protocol. EMG reflex activity of erector spinae (ES) and external oblique muscles were recorded in unexpected and in expected (self pre-activation) conditions. After fatigue, the normalized reflex amplitude of ES increased in expected and unexpected conditions (P<0.05) while ES response latency was slightly decreased. Reflexes latencies for ES were systematically shorter (P<0.05) of 25% in expected compared to unexpected conditions. These findings suggest that a large external force perturbation would elicit higher paraspinal magnitude responses and possible earlier activation in order to compensate the loss of muscular force after fatigue. Because of the seated position the postural adjustments were probably not triggered and thus explain the lack of abdominal activation. The self-anticipated pre-activation in order to counteract perturbations was not affected by fatigue illustrating the natural muscular activation to maintain trunk stability. © 2009 Elsevier Ltd.


Rupp T.,EA 2991 Motor Efficiency and Deficiency Laboratory | Girard O.,EA 2991 Motor Efficiency and Deficiency Laboratory | Perrey S.,EA 2991 Motor Efficiency and Deficiency Laboratory
Muscle and Nerve | Year: 2010

This study aimed to determine whether the timecourse of maximal resting H-reflex amplitude (Hmax) recovery after a prolonged moderate-intensity muscle contraction differs according to the optimal stimulation intensity used (predetermined vs. readjusted). Thirteen males performed a sustained isometric plantar flexion at 40% of their maximal voluntary contraction torque output until exhaustion. Hmax of the soleus muscle was recorded before and 2, 6, 10, and 14 min after the end of the contraction, then normalized by the respective maximal M-wave to form the H max/Mmax ratio. During recovery, pre- and redetermined optimal stimulation intensities (mini-recruitment curve drawn before each recovery measurement) were applied randomly to measure Hmax. When using redetermined stimulation intensities, normalized H-reflex values were systematically greater (+11, +16, +15, and +15% after 2-, 6-, 10-, and 14-min recovery periods, respectively) than those obtained with the predetermined intensity. Keeping the stimulation intensity constant to evoke Hmax after a sustained muscle contraction can underestimate the H-reflex facilitation occurring after exhaustive exercise. It is therefore more appropriate to redefine the optimal stimulation intensity to evoke Hmax (using mini-recruitment curves) when the purpose is to analyze spinal modulation during the recovery phase. © 2009 Wiley Periodicals, Inc.

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