Abstract

The sound (SMG) generated by the biseps muscle during isometric exercise at 2, 40, 60, and 80 of maximum voluntary contraction (MVC) up to exhaustion has been recorded by a contact transducer and integrated (iSMG), thogether with the surface electromyogram (EMG) in eight young untrained men. At the onset of exercise, iSMG and integrated surface EMG (iEMG) amplitude increased linearly with exercise iSMG remained constant for 253 +/- 73 (SD), 45 +/- 16, 21 +/- 5, and 0 s at the four levels od contraction. Then iSMG increased linearly at 20 MVC, fluctuated at 40 MVC, and decreaased exponeentially at 60 and 80 MVC. iSMG exhaustion-to-onset ratio was 5.0 at 20, 1.0 at 40, and 0.2 at 60 and 80 MVC. On the contrary, independently of exercise intensity, iEMG increased with time, being 1.4 higher at exhaustion than at the onset. The nonunivocal iSMG changes with time and effort of exercise suggest that the sound may be a useful tool to acquire different information to EMG and output force during muscle contraction up to fatigue. Verf.-Referat