Do you ever notice that sometimes when people have a problem with one of their lower extremities, there are arm swing changes? Usually on the opposite side? This can be anything from a short leg to lack of ankle dorsiflexion, lack of hip extension or even over pronation.
Many times, gait changes, including arm swing, are an "above down" process. This means it begins in the cortex, affects the pattern generators which subsequently will affect extremities distal to that. Sometimes this is a metabolic problem, sometimes vestibular (which can also be mechanical, causing decreased joint and muscle mechanoreceptor input to the cerebellum and vestibular nucleii), sometimes a combination of both. Throw a figure-of-eight ankle wrap on and walk. Your ROM is decreased (mechanical); this reduces input to your cerebellum which reduces input to your vestibular system. Your ankle dorsiflexion and step length will be diminished on that side; this will often cause an increase in arm swing on the contralateral side, which increases the metabolic "cost".
Arm swing may be coached, but we believe this is not always the correct approach as if it is a vestibular problem with altered cerebellar input (Something with the actual semicircular canals or perhaps input from muscle spindle or Golgi tendon organs), coaching arm swing makes the patient "look better" but does not really "fix" the problem; Which may be something as simple as joint pathomechanics, ligamentous restriction or a lack of skilled/endurance/strength in appropriate musculature. If it is a metabolic issue, sometimes coaching arm swing can improve mechanical efficiency but at the cost of decreasing cortical efficiency, because the brain is such an energy hog.
Arm swing is there for a reason. It tells you something about what is going on or what is not going on. Just because it looks bad does not mean that it is necessarily the problem. Look deeper and keep your eyes, ears and mind open.
We will be talking about the case with this gal. her crossover gait and armswing, alonng with 2 other cases, on our 3rd Wednesdays class on onlince.com: Biomechanics 320 on 8/15/2018
Meyns P, Bruijn SM, Duysens J. The how and why of arm swing during human walking. Gait Posture. 2013 Sep;38(4):555-62. doi: 10.1016/j.gaitpost.2013.02.006. Epub 2013 Mar 13.
Wu Y, Li Y, Liu AM, Xiao F, Wang YZ, Hu F, Chen JL, Dai KR, Gu DY. Effect of active arm swing to local dynamic stability during walking. Hum Mov Sci. 2016 Feb;45:102-9. doi: 10.1016/j.humov.2015.10.005. Epub 2015 Nov 23.