Relaxation electromechanical delay as a fatigue index in isokinetic concentric movement

Relaxation electromechanical delay (R-EMD) of knee extensors was used as a tool to quantify localized muscle fatigue during concentric isokinetic contraction. Eight subjects were asked to perform right knee isokinetic contractions at three angular velocities (120, 180 and 240°/sec). Mechanical work, knee angle, and four channels of quadriceps surface EMG were sampled simultaneously. Results indicated that: (1) R-EMD correlated with the mechanical work (R²=0.71, p<0.01); (2) the slope of R-EMD (Mean=1.86, SD=0.92) and initial EMD (Mean=105, SD=44.45) were stable relative to contraction EMD (C-EMD); (3) R-EMD could be influenced by contraction velocities; and (4) correlation was found between two pairs of electrodes which were placed over rectus femoris (R²=0.87, Slope=0.93)