Exercises for the torso performed in a standing posture: spine and hip motion and motor patterns and spine load

The purpose of this study was to document the muscle activity, spine motion, spine load, and stiffness during several movement-based or "functional" exercises and to assess the effect of technique change. Eight subjects, all healthy men from a university population, were instrumented to obtain surface electromyography of selected trunk and hip muscles, together with video analysis and electromagnetic lumbar spine position sensor to track spine posture. Exercises included a walkout in the sagittal plane that compared an upright form against a wall with those performed on the floor, overhead cable pushes, lateral cable walkouts, the good morning exercise, and the bowler's squat. Generally, muscle activation levels were quite modest even though the tasks were quite strenuous in many cases. Even though similar joint moments were required in different exercises, the pattern of activity between muscles was different. Abdominal bracing increased spine stiffness at the expense of more spine load. Thus, muscle activity seems to be constrained in "functional" exercises. There are several possible reasons for this. Single muscles cannot be activated to 100% of the maximum voluntary contraction in functional exercises because this would upset the balance of moments about the 3 orthopedic axes of the spine, or it would upset the balance of stiffening muscles around the spine required to ensure stability of the spinal column. The one exception was the floor walkout, which resulted in full activation of the rectus abdominis; however, this was a sagittal plane task without the joint moment constraints of multiplanar exercise. Therefore, maximal muscle activity is observed during single-plane tasks, but muscle activation levels were constrained during functional tasks. Thus, strength training muscles may not help in "functional multiplanar" tasks. These data can be used to assist decisions regarding the selection of exercises, specifically choices regarding the starting challenge, progression, exercise form, and possibly corrective technique for those who have spine concerns, or those simply looking for performance enhancement.