The relevance of increasing resistance on trunk muscle activity during seated axial rotation

Abstract

Objectives To investigate the electromyographic (EMG) trunk muscle activity during a low-load instrumented axial rotation exercise (Tergumed) and the relevance of increasing resistance. Setting Evaluation was done in a training centre in a university hospital. Participants Thirty healthy subjects without musculoskeletal or neuromuscular complaints. Main outcome measures The normalized (as a percentage of maximal voluntary isometric contractions (MVIC)) EMG activity of 14 abdominal and back muscles were investigated during dynamic trunk rotation exertions at 30%, 50% and 70% of maximum mean force (MMF). Results During the low-load (30% MMF) rotation exercise, the internal abdominal oblique muscle reached activity levels of 30% of MVIC. All the examined back muscles and the external abdominal obliques reached activity levels of 60% of MVIC. Increasing the resistance during seated axial rotation, created significantly higher relative muscle activity levels for all trunk muscles. Conclusions The results of the present study indicate that increasing resistance to 50% and 70% MMF during seated axial rotation in a Tergumed training device consistently created higher relative activity levels in all trunk muscles. In the vulnerable spine undergoing rehabilitation the results suggest that training at 30% MMF may be sufficient.