Effects of local fatigue on myoelectrical activity of erector spine muscles and the center for pressure displacement of the feet during balance recovery following postural perturbation in kyphotic subjects

Background: kyphosis deformity affects postural control. Muscular fatigue is one of the factors that can impair the mechanism of body balance. The aim of this study was to determine the effects of local fatigue on the myoelectrical activity of erector spine muscles and the center for pressure displacement of the feet during balance recovery following postural perturbation in kyphotic subjects.

Methods: In this quasi-experimental study, 12 male students with>40 degrees thoracic kyphosis and 12 controls were selected to participate in the study. A flexible ruler was used to measure thoracic kyphosis. For postural control assessment, each subject underwent unexpected, forward-backward perturbations while standing on a foot scan mounted on a movable plate triggered by a weight equivalent to 10% of the subjects’ body weight. Experimental procedure was measured before (3 trails) and after (3 trials) the fatigue protocol. The myoelectric activity of the erector spine and multi fidus was compared in the groups using repeated measures of ANOVA and independent t-test (P<0.05).

Results:  There was no significant difference in the foot center of pressure displacement in both groups after muscular fatigue. After fatigue, there was an increase in the activity of longissimus thoracis (P=0.001) and iliocostalis thoracis (P= 0.001) in control group, while no significant difference was reported for the muscular activity of multifidus (p=0.084). The activity of langisimus thoracis was significantly increased (P=0.028) in kyphtic group after fatigue.

Conclusion: erector spine muscles fatigue could not significantly affect the postural control in both groups, but the electrical activity of erector spine muscles during balance recovery following postural perturbation in kyphotic subjects was different than the controls.