Back muscle activity during locomotor tasks in inactive children / 体力科学

ABSTRACT

The electromyographic (EMG) activities of the back and thigh muscles while pedaling a bicycle ergometer at different load levels (300, 450, 600 and 750 kpm/min) and during walking and running at top speed up and down a staircase were investigated in children classified as physically less and more active than average. Each child underwent a battery of physical fitness tests to determine his physical fitness level relative to the national standard. Although the physiques of the inactive and active children did not differ, there were considerable differences between their back-lift, grip and knee-extension strengths, and the maximum anaerobic power, and 50-m dash performances of the two groups. The EMG data for each of the different tasks over selected periods (bicycle pedaling 5 complete revolutions, staircase task 5 stepping cycles) under different workload conditions were full-wave rectified and integrated (IEMG) . Under low workload conditions (ergometer tasks at 300 and 450 kpm/min and walking up and down stairs), the mean IEMG values (mIEMG) of all the muscles tested did not differ significantly in the inactive and active children. However, for all the higher workload tasks (pedaling at 600 kpm/min and running up and down stairs), the mIEMG values of the erector spinae muscles in the inactive children were significantly lower than those of the active children, and the difference increased gradually as the workload increased. This trend was even more marked when normalized mIEMG values were used. When the children ran up and down stairs at top speed, the inactive group had lower thigh, gluteus maximus and erector spinae muscle mIEMG values than the active group, and the difference between the normalized mIEMGs of the erector spinae muscles of the two groups showed a particularly strong statistical significance (P<0.01) when running both up and down stairs. As a similar trend was observed when the workload was maintained at a high level for the bicycle pedaling task, we concluded that at least part of the difference between the muscular activities of the two groups of children demonstrated when they carried out the running task was attributable to differences in the development of the muscle fibers and neuronal mechanisms of the erector spinae muscles.