Background: Analysis of electromyographic (EMG) activities in the back during dynamic exercise is needed because more complex loading on the spine is created in comparison with that during static exercise. The purpose of this study is to investigate the difference in bilateral midback and low-back paraspinal muscle (PSM) activities during performance of different resistance isokinetic exercises in healthy subjects and those with scoliosis.
Methods: Forty-one healthy subjects and thirty-three subjects with adolescent idiopathic scoliosis (AIS) were enrolled. An isokinetic back system in combination with quantitative surface EMG was used to evaluate the dominant and nondominant PSM activities by analyzing the root mean square (RMS) during isokinetic extension and flexion exercise at velocities of 30 degree/s and 90 degree/s.
Results: Significantly higher RMS of EMG were found in the dominant medial and lateral PSM of the lumbar region than the non-dominant muscles in the healthy control group and in those with AIS with smaller curves (<20 degrees) during isokinetic flexion and extension exercises. In AIS patients with larger curves (20 to 50 degrees), shifting of muscle activities from the dominant to the non-dominant side occurred during isokinetic exercises, and the EMG activities of the thoracic muscle were significantly higher on the non-dominant (concave) side than on the dominant (convex) side.
Conclusions: The bilateral PSM do not act symmetrically during isokinetic back exercises. The dominant lumbar PSM supply the major action in healthy subjects and patients with small curve scoliosis. For larger curve scoliosis, compensated muscle activity is needed in the midback when doing resistance exercises. More midback protection may be needed by scoliotic subjects with large curves during resistance exercise.