In some muscles, nonuniform surface electromyography (EMG) responses have been demonstrated within a muscle, meaning that the electrode location could be critical in the results of surface EMG. The current study investigated possible region-specific EMG responses within the human biceps femoris (BF) muscle. Surface EMG was recorded from various regions along the longitudinal axis of the BF muscle with 20 electrodes. Ten healthy men performed maximal isometric contractions of hip extension and knee flexion, which involve the BF muscle. The ratio of the EMG amplitude between hip extension and knee flexion tasks (HE/KF) was calculated and compared among the regions. There were no significant differences in HE/KF among the regions along the BF muscle (P > .05). This suggests that the entire superficial region of the BF muscle is equally regulated in the 2 different tasks. We suggest that the electrode location is not critical in estimating the activation properties and/or functional role of the superficial region, which corresponds with approximately 50% of the muscle length of the BF muscle, using surface EMG during maximal contraction.
Kohei Watanabe is with the Laboratory of Neuromuscular Biomechanics, School of International Liberal Studies, Chukyo University, Nagoya, Japan. Motoki Kouzaki is with the Laboratory of Neurophysiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan. Toshio Moritani is with the Laboratory of Applied Physiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.