So, R., Chan, K-M., & Sui, O. (2002). EMG power frequency spectrum shifts during repeated isokinetic knee and arm movements. Research Quarterly for Exercise and Sport, 73, 98-106.

This study investigated the interrelationships of muscle mechanical performance and EMG power frequency spectrum (mean power frequency - MPF) during repeated isokinetic knee extension and elbow flexion performed with maximal effort in elite athletes (M = 12; F = 6). Repetition speed for the two exercises was 180 deg/sec. Knee extension was performed for 50 repetitions and elbow flexion for 40 repetitions.

MPF and work output decreased as the exercises progressed. The nature of the decrease was particularly individual. The amount of MPF drop was ~36%.

Implication. Repetitious exercises about a joint requiring considerable effort produces considerable loss of power (~36%). Gauging the optimum power output to sustain a constant power output becomes a challenge for coaches. Starting "hard" would seem to have little validity as a reasonable coaching directive as it would only accelerate the onset of debilitative fatigue.

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