Tohoku J Exp Med. 1994 Jul; 173(3): 303-9.

The variation of action potential and impedance in human skeletal muscle during voluntary contraction.

Liao TJ, Nishikawa H.

Department of Oriental Medicine, Meiji College of Oriental Medicine, Kyoto, Japan.

We used an insulated acupuncture needle to deliver a 20 kHz alternative current to detect the changes on the electromyogram (EMG) and deep muscle impedance. We found that impedance increased (with a duration of 224.1 +/- 75.3 msec) and then decreased (with a duration of 293.4 +/- 97.3 msec) after motor unit action potential (MUAP) firing during isometric voluntary contraction (VC) of the tibialis anterior muscle (TAM). We divided the positive peak into pattern I (with a latency range of > or = 30 msec and < or = 75 msec) and pattern II (with a latency range of > 75 msec and < or = 140 msec). These patterns of change corresponded to the contraction times of tension caused by the electrical stimulation and VC. These impedance changes may be caused by a change in the extracellular and intracellular fractions, and may reflect the variance of tension intensity in the muscle tissue.