A wide range of electromechanical delay (EMD) values have been reported in the literature which attributed to either the biological characteristics of the subjects or the experimental methods adopted. The purpose of the present study was to investigate the normal range of EMD in different age and gender groups in normal healthy population under a consistent experimental condition. The subject sample consisted of 176 volunteers (91 males and 85 females) in an age range from 8 to 78 years. During testing the subject sat in a testing chair equipped with a force transducer connected to the lower leg. Surface electromyograms were recorded from the rectus femoris, vastus lateralis and vastus medialis muscles. Upon seeing a visual stimulus, the subject performed a maximal isometric knee extension. The findings in this study included: (1) the range of EMD values in the maximal isometric knee extension was from 20 to 100 ms; (2) the longest EMD value was found in the 8-12 year age group (p<0.05), there were no significant EMD variations found in the 13-16, 18-24 and 25-42 year groups, and EMD elongated in the 56-78 year group (p<0.05); (3) there was no gender difference in EMD in the overall subject population, however, in the 18-24 year group, the EMD of men was shorter than women (p<0.05); (4) significant correlation coefficients were found between EMD and maximal contraction force, the rate of force development, body height and mass (p<0.05); (5) there were no significant differences found between the mean EMD values of the vastus lateralis, rectus femoris and vastus medialis, however, EMDmax, ie. the longest EMD among the three muscles in each contraction, was significantly longer than the mean EMD values of the three muscles (p<0.05).
Zhou, S, Lawson, DL, Morrison, WE & Fairweather, I 1995, 'Electromechanical delay of knee extensors: the normal range and the effects of age and gender', Journal of Human Movement Studies
, vol. 28, no. 3, pp. 127-146.