Trunk Muscle Activation While Resisting Asymmetrically Applied Loads in an Axially Rotated Posture

The present investigation describes the electromyographic (EMG) response of eight trunk muscles during the application of loads to the torso while subjects maintained a twisted posture. The external moments of 20 and 40 Nm were applied to a harness system as each of the 10 subjects twisted 25 degrees. The applied moment direction was varied in 3 0 degree increments completely around the subjects (0 to 33 0 degrees). Surface EMG was used to monitor the left and right Latissimus Dorsi, Erector Spinae, External Oblique, and Rectus Abdominus. Multivariate and univariate analyses of variance (MANOVA and ANOVA) procedures showed significant main effects for all muscles and a significant moment magnitude by moment direction interaction effect in 6 of the 8 muscles. The greatest muscle activity was observed in the right Erector Spinae and the left External Oblique muscles. The results are also compared with an earlier study in which a similar loading paradigm was used as subject maintained a neutral upright posture.