Reproducibility of electromyography of muscular fatigue during isometric contraction of the quadriceps muscle

Abstract

The purpose of this study was to determine test-retest reliability of electromyography (EMG) during sustained fatiguing contractions of the quadriceps. Ten healthy subjects (five male, five female) were tested on two days, one week apart. Surface EMG was recorded from rectus femoris, vastus lateralis and vastus medialis during sustained isometric contractions at 80% of maximal voluntary contraction held to exhaustion. Quadriceps fatigue was described using three measures for recorded median frequencies (MDF): initial, final, and normalized. Collected initial, final and normalized values showed little variation, indicating similarity between the measures; high reliability (ICC, Intraclass Correlation Coefficient = 0.60-0.85) was found for all three muscle groups at contraction level. The gradual decline in median frequency values clearly
exposes the process of muscle fatigue, related to muscles' physiological changes. The high ICC values found point to reproducibility of measuring muscular fatigue during femoral quadriceps sustained contraction, showing that the proposed methodology is reliable and trustworthy, hence may be used to assess muscular fatigue.