Thursday, 8 November 2012

‘Windmill Arms’ and ‘Beating the Drum'

A post on the direction of arms and the flow-on effect to the pelvis and lower limb.

How often have you seen the windmill arm action or one arm doing something quite different to the other? You might ask, what difference does it make? You may also ask does it change biomechanics enough to make a difference? Let’s explore this from a practical perspective.

The arms are like a cadence monitor - if we want to accelerate we drive our arms faster to cause an action/reaction in our legs. Ideally both arms should move in a similar path matching our stride. This produces a more even stride with similar timing in the air and on the ground, left side to right side. But what happens if we have one arm moving relatively well and the other is externally rotating or waving out to the side?

Fig 1. You can see the right arm externally rotating. This runner is probably navigating a corner/road deviation however, a rotation of this magnitude in the arm should not occur.

What you will see is a slower arm drive on the side of external rotation. A few things are occurring;

·      The arm drive is slower as it travels a further distance (in a circular motion away from the body)

·      The contralateral leg has to react to this by slowing the swing phase slightly or producing an abducted leg swing (we’ve all seen these)

·      The lack of movement in a more linear plane will not take advantage of the stretch shortening cycle (SSC), (our ability to store and use kinetic energy). This stored energy is often considered free energy and is most evident in activities that produce eccentric actions with ground contact. This also occurs in running through out our posterior sling*

Fig 2. This runner is externally rotating his left arm (away from his body). This will probably change the right leg swing phase to an abducted (away) from the midline position.

This will appear as a jerky gait or someone that appears to have a slight limp. The arm swing in effect is slowing a portion of the gait. Another consideration is the loading on the opposite side. Does it increase time on the ground and loading in stance phase? This would be hard to prove unless a force plate is used. Needless to say it’s less than ideal.

A similar scenario in the lower limb can be caused by what a friend of mine calls ‘beating the drum’. This occurs when the arm extends back but does so from the elbow. taking the arm from about 90 degrees to 130-150 degrees. Again, this is slower not only because it has to travel further but also because more force is needed to propel a longer lever.

Does this increase injury? Again, this would be hard to prove. Having said that, if you do possess a musculoskeletal imbalance then this would most likely increase your injury risk.

Can you change this? Of all the biomechanical dealings with distance running I find this one the easiest and often the biggest change to running efficiency and perception. Changing arm swing would seem to be easier because you have more co-ordination and finer movement control over your upper limbs (more receptors per gram of tissue when compared to the pelvis and leg musculature).

Often there is an immediate change to the stride pattern and a more even running pattern. It also feels lighter on the foot strike to the same as the arm which externally rotates.

So the arms do more that just go back and forth, they can literally dictate actions of the lower limb and influence pelvic function. Next time you run, think about what your arms might be doing

* Posterior sling: An anatomical sling extending from our hamstring, sacrotuberous ligament, gluteus maximus, to the contralateral lumbo-dorsal fascia into our lats. This sling acts like a spring storing energy from side to side with each stride

No comments:

Post a Comment