Aim: 

The aim was to assess the effects of acute passive stretching on the electrical and mechanical response of a previously-fatigued muscle.

Methods: 

Eleven participants underwent maximal tetanic stimulations (50Hz) of the medial gastrocnemius, before and after a fatiguing protocol and after a bout of passive stretching applied on the fatigued muscle. During contraction, surface electromyogram (EMG), mechanomyogram (MMG) and force were recorded. The following parameters were calculated: i) the EMG root mean square (RMS), mean frequency (MF) and fibre conduction velocity (CV); ii) MMG peak-to-peak (p-p) and RMS; iii) the peak force (pF), contraction time (CT), half relaxation time (½RT), peak rate of force development (dF/dt) and its acceleration (d²F/dt²).

Results: 

Fatigue reduced pF by 18% (P<0.05) and affected the other force, EMG and MMG parameters. After stretching: i) all EMG parameters recovered to pre-fatigue values; ii) MMG p-p remained depressed to post-fatigue values, while RMS recovered to pre-fatigue values; iii) the pF, dF/dt and d²F/dt² were further reduced by 22, 18 and 51%, respectively, and ½RT by 40% (P<0.05).

Conclusion: 

Acute passive stretching, when applied to a previously fatigued muscle, further depresses the maximum force generation capacity. While stretching does not alter the electrical parameters, it additionally affects the mechanical behaviour of the muscle-tendon unit.