Action potential velocity measurements in the upper trapezius muscle.

The feasibility of action potential velocity (APV) measurements in the upper trapezius muscle with surface electrodes has been investigated. A four-bar electrode array connected to a double differential amplifier system was used. APV was estimated by a polarity correlation algorithm implemented on a PC computer. Six females and six males participated in the investigation. Attempts to get acceptable APV estimates were made in five electrode locations, 5 mm interspaced along the upper rim, beginning in the most distal part. Data were collected while holding out the arm horizontally in the sagittal plane. The results indicate that the method worked in five out of six males while it was difficult to get reliable estimates in the female group. Furthermore, the two most distal electrode locations gave the best results. In these two locations, the average APV for males was 4.8 m s(-1), sd 0.9. The difficulties in the female group were possibly due to small muscle dimensions and subcutaneous fat. Use of the double differential technique seems to be essential; attempts with the single differential technique were fruitless.