The effect of lumbar back support tension on trunk muscle activity

Objective. Assess the effect of different controlled lumbar back support ti ghtness levels on trunk muscle activity. Design. Two-way repeated measure design assessing lumbar back support tensi on and submaximal trunk extension moments on trunk muscle electromyographic activity. ackground Biomechanical studies on lumbar back supports often use electromy ography (EMG) to assess the affect on trunk muscle activity. However, the l umbar back support may alter the electromyographic signal by changing the e lectrode-muscle distance. Methods. Subjects performed trunk extensions at three static submaximal ext ension moment levels (25%, 50% and 75% MVC) while stabilized at the hips an d shoulders, with the back support tensioned to three different tightness l evels (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 (P less t han or equal to 0.05) of lumbar back support tension on the average normali zed EMG across the 10 trunk muscles sampled. Conclusions. For static experimental tasks, as long as electrodes are prote cted from direct contact with the back support, studies assessing the effec t of lumbar back supports on the trunk muscles via ER IG during static task s are not subject to confounding due to differences in tensions across subj ects.