Electromyographic analysis of four techniques for isometric trunk muscle exercises.

Posture to avoid hyperextension of the lumbar spine during isometric trunk muscle exercises has been widely recommended. However, there are no common standards for cervical and pelvic alignment during exercises. To investigate the effects of four different techniques regarding cervical and pelvic alignment, electromyographic (EMG) and radiological studies were performed on 30 healthy subjects. The four different postures were: (1) maximally extended neck, (2) neutral neck, (3) maximally flexed neck, and (4) maximally flexed neck with pelvic stabilization through muscle contraction. During flexion exercises, the largest increase in EMG activity in the abdominal muscles was observed with the flexed neck with pelvic stabilization (p < .01). During extensor exercises, the largest increase in EMG activity in the erector spinae was also obtained in the same position (p < .01). An increase of EMG activity in antagonist muscles (eg, erector spinae on flexion, and rectus and oblique muscles on extension) was also greatest with the flexed neck and pelvic stabilization. From the radiographic study, degrees of lumbar lordosis were least with the flexed neck and pelvic stabilization (p < .01). This study showed that neck and pelvic alignment can influence the EMG activity of trunk flexors and extensors during isometric trunk exercises. For isometric trunk muscle exercises, a maximum flexed neck with pelvic stabilization through muscle contraction seems to be the most optimal posture for decreasing the lumbar lordosis and for activating trunk flexors and extensors most effectively.