Test-retest reliability of EMG and peak torque during repetitive maximum concentric knee extensions

The aim of this study was to investigate the reliability of peak torque and surface electromyography (EMG) variable's root mean square (RMS) and mean frequency (MNF) during an endurance test consisting of repetitive maximum concentric knee extensions. Muscle fatigue has been quantified in several ways, and in isokinetic testing it is based on a set of repetitive contractions. To assess test-retest reliability, two sets of 100 dynamic maximum concentric knee extensions were performed using an isokinetic dynamometer. The two series were separated by 7-8 days. The subjects relaxed during the passive flexion phase. Twenty (10 men and 10 women) clinically healthy subjects volunteered. Peak torque and EMG from rectus femoris, vastus medialis, vastus lateralis and biceps femoris were recorded. RMS and MNF were calculated from the EMG signal. The reliability was calculated with intraclass correlation coefficient ICC (1.1) and standard error of measurements (SEM). The reliability of peak torque was good (ICC = 0.93) and SEM showed low values. ICC was good for absolute RMS of rectus femoris (ICCgreater than or equal to0.80), vastus medialis (ICCgreater than or equal to0.88) and vastus lateralis (ICCgreater than or equal to0.82) and MNF of rectus femoris (ICCgreater than or equal to0.82) and vastus medialis (ICCgreater than or equal to0.83). Peak torque, and MNF and RMS of rectus femoris and vastus medialis are reliable variables obtained from an isokinetic endurance test of the knee extensors. (C) 2003 Elsevier Science Ltd. All rights reserved.