Activation patterns of postural muscles during bilateral arm flexion in children

Abstract

  We investigated activation patterns of postural muscles during bilateral-arm flexion in children. Subjects comprised healthy 14 boys and 11 girls aged 6 years. In response to a visual stimulus presented at 1-3 s after a warning signal, the subjects initiated bilateral arm flexion as quickly as possible and then stopped their arms voluntarily at a horizontal position. After 5 practice trials, test trial was performed 10 times with a 30 s-rest between the trials. Electromyograms (EMG) were recorded from the tibialis anterior (TA), gastrocnemius (GcM), rectus femoris (RF), biceps femoris (BF), and anterior deltoid (AD). The relative number (%) of subjects who showed the EMG burst of postural muscle was 80% in TA, 100% in GcM, 68% in RF, and 100% in BF. The relative frequency (%) of the trials in which the EMG burst was observed was higher in the following order; 57% in GcM only, 26% in TA-GcM, and 5% in TA only for the lower leg, and 65% in BF only, 30% in RF-BF, and 2% in the RF only for the thigh. Start time (mean ± standard deviation) of each muscle with respect to onset of AD was earlier in the following order; TA (-16 ± 39 ms), BF (20 ± 19 ms), GcM (43 ± 29 ms) and RF (47 ± 51 ms). In the children, unlike adults, TA was also activated in many subjects and the preceding activation to AD was not observed in BF. In addition, large inter- and intra-individual differences were indicated.