If walking is a learned activity, we can assume that running falls into that same category. Most of the literature on the biomechanics of locomotion has involved walking, and not nearly as much is known about running. Like walking, an individual's running pattern is developed anywhere between the ages of two and eight. Many runners appear to have developed an effortless, almost perfect action, yet others seem to develop a very inefficient and potentially injurious technique.
Runners constantly undergo unbalanced stress on normal body parts. These biomechanical errors are induced by multiple factors, such as the tendency of many runners to run on the same side of the road or the same way around a track. As these asymmetrical forces stress the body, there can be profound musculoskeletal effects; eventually leading to overuse injuries, which is a common complaint presented in chiropractic offices. If unidentified and untreated, these injuries can lead to severe or even permanent disability, such as short leg syndromes.
Through measurements made of treadmill walking/running in our Gait Laboratory, we've noticed that the stillest part of a runner's body is the head. It appears that carriage of the head is even smoother than that of the center of gravity. In fact, in walking the head appears to remain so still, that it's as if one could balance a glass of water on their head. In contrast, in the literature, smoothness of motion of the center of gravity (commonly referenced as b/t the umbilicus and the pelvis) has traditionally served as the central focus of gait mechanics. Perhaps, smoothness of the center of mass actually occurs as a result of intentions to provide for smooth head carriage? Thus, we propose that this apparent need to maintain smooth head carriage can actually be seen to link asymmetry in the lower body with asymmetry in the upper body. Hence, in runners who demonstrate obvious pelvic asymmetry (functionally related to leg-length inequality), we hypothesize that active asymmetrical control of the spine will be called upon as a form of compensation. In future work, we will seek to determine the correlation between measurements of head motion, with measurements of asymmetry in both the upper and lower body.