Myoelectric spectral analysis and strategies for quantifying trunk muscular fatigue.

Objective techniques for assessing trunk musculature with respect to fatigue-related characteristics do not exist. Based on work that relates frequency spectral shift in myoelectric signals to muscular fatigue at other body sites, a study was carried out to investigate and evaluate strategies for application of these techniques to the lumbar musculature. Through evolution of test administration procedures to reduce test time and discomfort as well as data interpretation methods to account for interindividual variability observed in data, an approach was developed for objective measurement of fatigue rate. While abdominal and lumbar muscle groups were assessed in 40 healthy subjects with results presented for 50% and 100% maximum voluntary contraction load levels, the methodology is discussed with emphasis on erector spinae results. The approach involves a normal function fatigue plot. The plot relates fatigue rate as measured by myoelectric spectral characteristics to muscle load normalized by body weight and is independent of the maximum voluntary contraction concept. This relationship forms the basis of comparison of the measured fatigue rate for a subject with questionable function to expected normal values determined from the plot, given the measured load level.