Background
Electromyography (EMG) is useful in investigating muscle activation; however, noninvasive evaluation of surface EMG is limited due to its complicated waveform. This study investigated muscle structure and activation using an analysis technique for surface EMG.
Material and Method
Surface array electrodes were used in 17 healthy male subjects to record eight-channel EMGs from each biceps brachii muscle during voluntary isometric contraction with a 1-kg weight band with the subjects seated. The peaks detected by referenced EMGs were normalized and averaged as averaged pulses (APs) and the innervation zone (IZ) was estimated from the APs. Muscle fiber conduction velocities (MFCVs), estimated by the time difference of the peaks (method P) and by cross-correlation (method CC) by APs, were compared. Time periods with positive values around the central peak in AP (PP) were measured and the contribution of MFCVs by motor unit action potentials (MUAPs) was estimated.
Results
IZs were estimated in 12 subjects. Near the IZ, correlation between MFCVs by methods P and CC was lower than in other locations; MFCV was significantly larger by method P than by method CC in the vicinity of the IZ. PP of the comparison AP was significantly larger than that of the reference AP. The distribution of the MFCVs by different MUAPs was verified by computer simulation.
Conclusions
Surface EMG was used to demonstrate the diversity of MFCVs, with some increased MFCVs, for several MUAPs in the vicinity of the IZ. This method could be applied to the evaluation of neuromuscular disorders.

Keywords: Neural Conduction - physiology, Muscle Fibers, Skeletal - physiology, Isometric Contraction - physiology, Electromyography - methods, Electrodes, Arm - physiology, Action Potentials - physiology, young adult