Acute passive stretching in a previously fatigued muscle : electrical and mechanical response during tetanic stimulation

The aim of this study was to assess the effects of acute passive stretching on the electrical and mechanical response of a previously fatigued muscle. Eleven participants underwent maximal tetanic stimulations (50 Hz) of the medial gastrocnemius, before and after a fatiguing protocol and after a bout of passive stretching of the fatigued muscle. During contraction, surface electromyography (EMG), mechanomyography (MMG), and force were recorded. The following parameters were calculated: (1) the EMG root mean square (RMS), mean frequency, and fibre conduction velocity; (2) MMGpeak-to-peak and RMS; (3) the peak force, contraction time, half-relaxation time, peak rate of force development (dF/ dt) and its acceleration (d2F/dt2). Fatigue reduced peak force by 18% (P50.05) and affected the other force, EMG, and MMG parameters. After stretching: (1) all EMG parameters recovered to pre-fatigue values; (2) MMG peak-to-peak remained depressed, while RMS recovered to pre-fatigue values; (3) the peak force, peak rate of force development and its acceleration were further reduced by 22, 18, and 51%, respectively, and half-relaxation time by 40% (P50.05). In conclusion, acute passive stretching, when applied to a previously fatigued muscle, further depresses the maximum forcegenerating capacity. Although stretching does not alter the electrical parameters of the fatigued muscle, it does affect the mechanical behaviour of the muscle–tendon unit.