Quadriceps mechano- and electromyographic time-frequency responses during muscular contractions to volitional exhaustion.

INTRODUCTION

Surface electromyography (SEMG) and mechanomyography (SMMG) responses of the quadriceps during muscular contractions to exhaustion were computed and analyzed by analysis of variance and polynomial regression analyses.

METHODS

Participants performed maximum flexion-extension movements at 180°/s until volitional exhaustion, rested for 2 minutes, and then completed a second bout of movements until exhaustion. Torque and SEMG/SMMG median frequencies and amplitudes were examined at 9 points across repetitions completed.

RESULTS

(1) Torque decreased precipitously; (2) SEMG amplitude displayed an initial increase, then a steady decrease, and SMMG amplitude showed a continuous decrease; and (3) SEMG and SMMG median frequencies displayed a continual decrease over repetitions completed. Fractional polynomial and quadratic models explained the fatigue process with the highest precision.

CONCLUSIONS

Changes in electrical and mechanical properties of the quadriceps during fatigue reflect alterations in neuromuscular activation strategies and/or muscle wisdom. SEMG frequency modeled muscle fatigue more effectively than amplitude, whereas SMMG frequency and amplitude were equally effective.