Electromechanical response times and muscle elasticity in men and women

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Abstract
The purpose of this study was to compare the delay in performance attributable to muscle elasticity in men and women. A group of 11 active young men age (mean, SE) 21.9, 0.7 years, stature 1.780, 0.020 m, body mass 76.4, 3.2 kg and 11 women age 20.9, 0.4 years, stature 1.670, 0.020 m and body mass 61.9, 2.6 kg provided written informed consent and were recruited to the study. In response to an acoustic signal delivered via headphones, the subjects performed a plantar flexion movement of the preferred leg as quickly as possible. A seated position ensured that the knee of the subject was flexed at a right angle and that the shank was vertical. The ball of the foot was on a force platform which was used detect the onset of muscle tension and the heel rested on a pressure pad which was used to identify movement. Surface electrodes sensed electromyographic activity (EMG) in the soleus muscle. Force platform output was captured by a digital storage oscilloscope and recorded via a y-t pen recorder for subsequent analysis. A separate timer was used to determine total reaction time (TRT). Premotor time (EMGT) was taken to be the time interval from the delivery of the signal to change in EMG. Electromechanical delay (EMD) was the time interval between the change in EMG and movement and was subdivided into force time (FT) i.e. the time interval between EMG and the onset of muscle tension and elastic charge time (CT) i.e. the time interval between the onset of muscle tension and movement. The subjects performed ten trials and in most cases the mean of ten readings was used to determine TRT, EMGT, EMD, FT and CT. There were no differences between men and women in TRT (163.3, 5.6 ms vs 176.2, 6.3 ms; P=0.149), EMGT (123.6, 6.0 ms vs 131.8, 6.4 ms; P=0.359) and FT (9.5, 1.1 ms vs 10.9, 1.2 ms; P=0.400) whereas there were differences in EMD (39.6, 1.2 ms vs 44.9, 2.0 ms; P=0.037) and CT (30.2, 1.3 ms vs 34.1, 1.3 ms; P=0.044). The results suggest that there are sex-linked differences in musculotendinous elasticity and these might in part account for observed performance differences.