Characteristics Of Electromechanical Delay In The Elderly

Abstract

Electromechanical delay (EMD) refers to the time lag between the onset of electrical activity (electromyogram: EMG) and tension development in skeletal muscle. Aging may influence this EMD as a hypothesis. PURPOSE The purpose of this study was, by measuring muscle reaction times and muscle strength in the condition that the eccentric (ECC) and concentric (CON) muscle actions of the lower limb for the elderly and young subjects, to investigate the characteristics of elderly people' s EMD, various reaction times and eccentric and concentric muscle strength from comparison with the young. METHODS A group of 13 elderly and 15 young healthy female subjects signed informed consent for volunteered to participate in this experiment. Their average age, height, and weight were 73.9 (SD 5.2) years, 149.4 (SD 5.0) cm, 49.7 (SD 5.5) kg (elderly group) and 18.9 (SD 0.7) years, 159.2 (SD 4.8) cm, 49.6 (SD 5.5) kg (young group), respectively. The measurement was performed for extension movement of knee joint, and surface EMG waveform was recorded from rectus femoris. RESULTS Concerning peak torque values of elderly group [ECC: 134.0 (SD 26.1) Nm, CON: 41.2 (SD 11.7) Nm], there were significantly low values (ECC: p<0.05, CON: p<0.01) than young group [ECC: 156.4 (SD 27.8) Nm, CON: 79.3 (SD 23.3) Nm] in both ECC and CON muscle strength. EMD of elderly group [ECC: 101.7 (SD 9.7) ms, CON: 92.7 (SD 13.1) ms] were significantly longer (ECC: p<0.05, CON: p<0.01) than young group [ECC: 82.8 (SD 10.9) ms, CON: 87.8 (SD 10.9) ms] in both ECC and CON muscle actions. Similarly, total reaction time (TRT) and pre-motor reaction time (PMT), there were significant difference (p<0.01∼p<0.001) between elderly group and young. CONCLUSIONS These results suggested that EMD and the muscular work according to increase in age were decreased and declines of these neuromuscular system were considered to may cause of fall during a walk and occurrence of injuries.