Arm Swing Part 3: Running Downhill on Uneven Terrain.
Today we have a pretty cool video for you. It is perfect stuff for a Sunday blog post. It is called “The Chase”. This team has done something pretty neat and this probably took alot of time to complete. Notice it is the same guy in two different outfits (red chasing black), giving the impression of him chasing himself. It is about pushing yourself to be the best you can. But there are some clips at 2:17 we want you to pay attention to. Watch his arm swing when he is scrambling down the hill. The arm swing is tight, controlled and helps his core and balance. But there are other costs to doing this, and it gives perfect support to our blog posts from a few weeks ago on arm swing.
If you have not read our posts from December 7-8 (link) it might behoove you to read them now otherwise today’s topic will have limited meaning to you. We are building on this topic of limb swing, and how some of it is passive and some is active from a neurologic control standpoint.
So, we are back to looking at limb swing again. Particularly arm swing today. It is important for you to realize, as put forth in:
Huang et al in the Eur Spine Journal, 2011 Mar 20(3) “Gait Adaptations in low back pain patients with lumbar disc herniation: trunk coordination and arm swing.”
that as spine pain presents, the shoulder and pelvic girdle anti-phase begins to move into a more “in-phase” favor. Meaning that, the differential between the upper torso twist and pelvic twist is reduced (in the drawing above the lines will laterally converge). In our opinion, in threatening motor challenges (such as running downhill at 2:17 in the video above) the body will create a reduction in spine rotation and motion due to the increased activation of the core to maintain balance and stability. IF this anti-phase is reduced then arm swing will be reduced (as is seen when he is scrambling downhill). The central processing mechanisms do this to reduce spinal twisting, because reduced twist means reduced spinal motor unit compression and this hopefully leads to less pain but also more body control. The consequence to this reduced spinal rotation is reduced limb swing. Think about this next time you see someone, a runner patient or athlete, with reduced arm swing especially on one side. Furthermore, according to
Collins et al Proc Biol Sci, 2009, Oct 22
“Dynamic arm swinging in human walking.”
normal arm swinging requires minimal shoulder torque, while volitionally holding the arms motionless requires 12 % more metabolic energy, proving that there are both active and passive components to arm swing. Collins also discovered that among measures of gait mechanics, vertical ground reactive moments are most affected by arm swinging and increased by 63% without it. Wow, 63% !
So, taking this data, one could extrapolate that energy consumption is increased running downhill on uneven terrain. This may be nullified by moving with gravity and the downhill slope. But on such uneven terrain, if you are smart and not reckless you will be expending energy to slow the downhill chaos so you can remain in control of the descent. This goes for flat uneven or slippery terrain as well, keep this in mind when you hit some icy patches this season. Thing of The Gait Guys, and note how your body adapts to the surface. The surface has huge impact on how you use your body.
So, it is all about efficiency and protection. Efficiency comes with fluid unrestricted movements and energy conservation but protection has the cost of wasting energy and reduced mobility through a limb(s) and spine.
For you neuro nerds, remember the receptors from the central spine and core fire into the midline vermis of the cerebellum (one of the oldest parts of our brain, called the paleo cerebellum); and these pathways, along with other cerebellar efferents, fire our axial extensor muscles that keep us upright in the gravitational plane and provide balance or homeostasis. And when running downhill you had better be firing your extensors !
Shawn and Ivo … combining almost 40 years of orthopedics, neurology, biomechanics and gait studies to get to the bottom of things….. to help you become better athletes, better coaches, and better doctors.