Objective:To study the correlation between duration and amplitude of motor unit potentials(MUPs) in limb muscle.Methods:MUPs were recorded in 392 blocks of muscles including biceps brachii

abductor pollicis brevis

quadriceps femoris and tibialis anterior in 165 subjects who were different in gender and age.The correlation between duration and amplitude were analyzed by statistical methods.Results:The correlation coefficient between duration and amplitude was 0.54.The duration-amplitude curve was like transverse S type;and it was gentler and had less error bars in duration of 9.6ms to 11.5 ms.The error bars of amplitude enlarged remarkably beyond the area.The amplitude-duration ratios of different muscles

genders and ages in duration of 9.6ms to 11.5ms had no significant deviation(P=0.44

P=0.21

P=0.22).Conclusion:There is obvious correlation between amplitude and duration but may be irrelative to the musculature

gender and age.This is a stable electrical characteristic of skeletal muscle motor unit.The variability of amplitude rises apparently when beyond a certain duration range.