Motor Unit Estimates Through Accelerometry

Abstract

Accelerometers were used to measure evoked peak limb acceleration (EPLA) for the fourth (index) finger. EPLAs were used to investigate force properties of motor units (MUs) and estimate their numbers in the first dorsal interosseous (FDI) through clustering in the force versus stimulus amplitude relationship. This system was semi-automated using a personal computer with A/D and D/A facilities. Upon repeated excitation, some MUs would potentiate and increase their force contribution by 3 to 4 times. It was found that MU number estimation procedures based on force that do not consider twitch potentiation may be underestimating MU numbers. A disadvantage of using EPLA for MU estimation is that sensitivity may vary between subjects due to finger weight and joint dynamics.