In an age where we can divert most of our attention to our phones, and still be able to walk at the same time, I start to wonder whether our arm swing is still relevant. Is it becoming a less than necessary motor skill in society and hence the need the rehabilitate it?
The answer is no.
Try this – walk at your normal pace and hold your phone up and look at it as if you are reading. Then pick up your walking pace and start breaking into a run. The faster you go, the more you have to let your phone down and swing your arms with your legs.
It’s not that it’s because it takes more concentration to run, and therefore we need to remove the attention taken up by the phone, but because our spinal cord and brain circuitry demand arm swing to assist in the following areas:
Energy Conservation
As paradoxical as this may sound, arm swing actually saves energy, rather than uses more of it. In an experiment, researchers look at 4 conditions of arm position:
1. opposite arm swing (normal)
2. swung in the same direction (anti-normal)
3. arms bound down by their sides
4. actively held arms by their side
They found that normal arm swing is most energy efficient, by 26% compared to the least efficient mode which is anti-normal. (Collins et al, 2009)
Think of anyone who has had a stroke and cannot use move his or her arm voluntarily. It either hangs by their side limply (condition 3), actively contracted against their body (condition 4) or it involuntarily moves often in the same direction as the advancing leg (condition 2). So with this level of energy cost per step, it is no wonder people with stroke or other neurological conditions with both arm and leg involvements struggle to walk effectively.
So treatment of this supposedly redundant motor activity is actually a key part of neurological rehabilitation. The goal of therapy is therefore to minimise the interference of the arms in walking, such that even limp and flaccid arms are more desirable than involuntarily flexing ones.
Similarly, in people with spinal cord injury, you can have incomplete quadriplegics with poor arm movement and reasonable leg movement, and can walk but lack arm swing. And more interestingly, incomplete paraplegics can have overactive arms which impede their ability to use their legs in this energy efficient and coordinated fashion.
Balance and Ground Reaction Force
Watching a toddler learn to walk shows us a glimpse into our neurological development of balance and stability. They typically walk with high steps and arms held out and high, to assist with balance. This is because it is difficult for them to control their balance and also the forces that the ground exerts back on their bodies as they stamp each foot.
Similarly, if you have to go down or fall onto a big step, notice that your arms come up to help stabilise you. The further you advance your leg down, the higher your opposite arm comes up.
Meyns et al (2013) discussed in their review paper that arm swing is needed for helping our bodies cope with the every changing perturbations of our environment we walk in. No matter how hard we try, each step we take is slightly different from the last and yet our bodies can cope with this array of micro-challenges successfully a thousand times over each day.
The answer lies, amongst other things, with arm swing.
When we walk, the ground reaction force that comes back up at us through our feet get absorbed by the legs and trunk and whatever is left is dissipated through our arms in the form of swing. Our trunk and shoulders, which govern arm swing, then can either engage or disengage depending on the level of balance and force required. So this suggests that arm swing is partly active and partly passive.
Therefore, in neurological rehabilitation, as therapists we have to think about ways to treat the body to allow the arms to be play both active and passive roles during walking, standing and moving between transitions. There is a lot of emphasis in the literature about how patients need to be more active, but my question is, are they being active in the right places, at the right times?
Resources:
Collins, S. H., Adamczyk, P. G., & Kuo, A. D. (2009). Dynamic arm swinging in human walking. Proceedings of the Royal Society of London B: Biological Sciences 276(1673):3679-88
Meyns, P., Bruijn, S. M., & Duysens, J. (2013). The how and why of arm swing during human walking. Gait & posture, 38(4), 555-562.
