The interrelationships between EMG, peak torque and perceived fatigue during repeated maximum isokinetic knee flexion with and without active knee extension

Abstract

This study of the knee flexors and extensors investigated the interrelationships between peak torque, mean power frequency (MPF) and the signal amplitude (RMS: root mean square) of the EMG and perception of fatigue throughout repeated dynamic contractions when the contraction cycle included maximum performance of both the agonists and the antagonists. Ten females performed two tests, which consisted of 100 repeated maximum knee flexions with passive or active knee extensions using an isokinetic dynamometer with simultaneous surface EMG. Peak torque and MPF displayed a pattern with two phases throughout both tests-a steep decrease during the initial 40 contractions followed by a period of stabilisation (the endurance level). In agreement with earlier studies, peak torque and MPF were stable, while the perception of fatigue increased at the endurance level. These results question whether MPF shifts can be used to detect risk situations, with respect for example to work-related myalgia, for endurance-profiled muscle fibres.

The principal patterns were unaffected by the contraction status (active or passive) of the extension phase, but the levels of output and MPF were affected when both phases of the contraction cycle were active. These results challenge the claims for the effects of certain PNF techniques.