Trunk muscle fatigue in subjects with a history of low back pain and a group of healthy controls measured by similarity index

Abstract

Trunk muscle fatigue has high relevance in human performance. Most authors agree that the use of the median frequency is preferred as a fatigue indicator. Most work has to date, been done on dynamic fatigue measurements, using the similarity index (SI). Repeated trunk flexion-extensions were measured using the B200 Isostation. Muscle activity was recorded by surface electromyography (EMG) in order to evaluate fatigue of trunk flexor and extensor muscles. Twenty male university students participated in this pilot study, including 6 apparently healthy subjects with a history of low back pain (LBP), and 14 healthy matched controls. All participants were instructed to perform repeated trunk flexion-extension against 50% of their back extensors maximal volutary contractions (MVCs) resistance until they could no longer perform the task. The SI was calculated from quantitative analysis of EMG data recording during dynamic trunk flexion extension task. Median frequency was also measured before and after fatiguing contractions. The results of this study revealed a significant decrease in the SI and median frequency measurements following fatigue in both groups (p< 0.05). The results of this study indicated that in both groups changes in SI measurements following fatigue are in agreement with the changes in median frequency measurements.