Trapezius muscle fatigue and electromyographic frequency analysis

• This study, comprising 6 separate articles, is concerned with different validity and reliability aspects of the electromyogram mean power frequency (MPF) as an estimator of localized musele fatigue in the trapezius muscle. A series of new, and partly controversial and problematic findings are reported.There was a systematic variation of MPF that was not related to muscle fatigue, but to other factors such as shoulder joint angle, torque and external hand load, which can erroneously be interpreted as muscle fatigue; the largest variation, ±8%, was related to joint angle; movements of the surface electrodes was the most probable explanation of this variation and thus significantly influence the MPF estimates; there was an unacceptably large random variation of single MPF estimates; single estimates should not be used for normalization of MPF; there was no correlation between MPF and subjective muscle fatigue at low load level; MPF did not work as a valid estimator of localized muscle fatigue at low load level; load dose was not a suitable parameter to represent physical stimulus at the evaluation of subjective fatigue; the EMG response to fatigue seemed to be different in healthy muscle compared with diseased muscle in patients with unilateral work-related trapezius myalgia; the changes were more pronounced on the healthy side.All these factors have to be considered if MPF is to be used as an estimator of localized muscle fatigue. Procedures are proposed to overcome some of these difficulties and reduce some of the variations such as a standard procedure for calibration, repeated measurements, regression procedures with calculation of trends insted of evaluation of single MPF estimate etc. There is a need for more research concerning the variation of MPF and procedures to handle this variation.

Nyckelord

EMG

Spectrum

Frequency

Fatigue

Trapezius

Myalgia

MEDICINE

MEDICIN

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