The influence of fatigue on trunk muscle responses to sudden arm movements, a pilot study

Objective. To examine fatigue induced changes in trunk muscle latencies following trunk muscle fatigue. Design. A repeated measures within subject design. Background. Trunk muscle responses to sudden movements is of interest in clinical biomechanics and motor control. Methods. Electromyographic profiles were recorded from transversus abdominis (finewire), internal oblique, rectus abdominis and external oblique and longissimus at the level of the 3rd lumbar vertebrae bilaterally. Four asymptomatic subjects performed arm-raising task using a visual cue before and after an isometric fatiguing trunk extension task. Results. Feed-forward responses were not detected in all muscles for every trial. In general, following fatigue trunk muscle onset latencies occur earlier (left, P=0.0016; right, P=0.0475). Conclusions. Trunk muscle fatigue alters anticipatory postural adjustments in normal subjects. It remains unclear if there is a pattern for specific muscles changes between individuals and if these are reflected in individuals with low back pain.