The effect of lumbar back support tension on trunk muscle activity

Objective. Assess the effect of different controlled lumbar back support tightness levels on trunk muscle activity. Design. Two-way repeated measure design assessing lumbar back support tension and submaximal trunk extension moments on trunk muscle electromyographic activity. Background. Biomechanical studies on lumbar back supports often use electromyography (EMG) to assess the affect on trunk muscle activity. However, the lumbar back support may alter the electromyographic signal by changing the electrode–muscle distance. Methods. Subjects performed trunk extensions at three static submaximal extension moment levels (25%, 50% and 75% MVC) while stabilized at the hips and shoulders, with the back support tensioned to three different tightness levels (44.5, 66.7 and 89.0 N) as well as a no-back support condition. Results. Statistical analysis failed to find a significant effect (Pless-than-or-equals, slant0.05) of lumbar back support tension on the average normalized EMG across the 10 trunk muscles sampled. Conclusions. For static experimental tasks, as long as electrodes are protected from direct contact with the back support, studies assessing the effect of lumbar back supports on the trunk muscles via EMG during static tasks are not subject to confounding due to differences in tensions across subjects.