Arm Swing and dynamic stability of the system.

We have discussed the arm swing issue so many times over the years that we have lost count. By many sources, arm swing is a product of lower limb action and a product of the effective, or ineffective, relationship between the shoulder "girdle" (maybe thoracic rotation component) and the pelvic girdle (lumbopelvic rhythm) during gait.  This is the concept of phasic and anti-phasic limb swing. If you want to dive into that, and you should if you are unfamiliar with the concept, you can look it up on our blog using the search box.  We are not to forget that the arms, and thus arm swing, is a major factor in maintaining balance. We have used the term "ballast" many times to describe the effects of arm swing, rotation, abduction, circumduction etc on assisting balance maintenance of the body during various locomotion strategies. These are largely subconscious actions, hence why we agree with the research suggesting that arm swing is secondary, compensatory, and takes its queues off of the activity of the lower limb motor actions. In essence, arm swing variants are necessary compensations to assist in maintaining things like balance, center of pressure, equilibrium and the like. 

In this recent 2017 study, we have another suggesting arm swings function in assisting, even improving, dynamic stability. We are reminded of MdGill's suggestion, and the concepts of phasic and antiphasic torso-pelvis counter rotational movements, of how spinal loads can be affected by changes or differences in arm position.  Even arm position changes in sitting and standing can alter spinal loads, so during movement it is a virtual guarantee. 

This study looked at "how arm swing could influence the lumbar spine and hip joint forces and motions during walking." In this study, the researchers had each subject perform walking with different arm swing amplitudes and arm positions. Here is a comment from the researchers on what they found, it is pretty much what we have been writing about for several years based off of other research"

"The range of motion of the thorax with respect to the pelvis and of the pelvis with respect to the ground in the transversal plane were significantly associated with arm position and swing amplitude during gait. The hip external-internal rotation range of motion statistically varied only for non-dominant limb. Unlike hip joint reaction forces, predicted peak spinal loads at T12-L1 and L5-S1 showed significant differences at approximately the time of contralateral toe off and contralateral heel strike."

Thus, we find yet another study confirming what many will say is obvious, that being arm position and movements have notable effects on whole body kinetics and spinal loads. This study suggested that arm variations did not have an effect on spinal loads during walking. We find this curious; it is something we will be looking into, and pondering. We hope you do as well.

Effect of arm swinging on lumbar spine and hip joint forces. Lorenza Angelini et al. Journal of Biomechanics, Sept 2017
http://www.sciencedirect.com/science/article/pii/S0021929017304670