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

ObjectivesTo investigate the electromyographic (EMG) trunk muscle activity during a low-load instrumented axial rotation exercise (Tergumed) and the relevance of increasing resistance.SettingEvaluation was done in a training centre in a university hospital.ParticipantsThirty healthy subjects without musculoskeletal or neuromuscular complaints.Main outcome measuresThe 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).ResultsDuring 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.ConclusionsThe 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.