Wednesday, February 29, 2012

(Your) Back In Action

This week’s contribution is provided by long-time colleague and Biomechanic, R. Barry O’Donnell, M.S. Barry comes with some impressive credentials including being a member of the 1976 US Olympic wrestling team.

We rigorously defend our lift-drag protocol as far safer than the bent-over technique used in other settings. For this reason: safety, we’re emphatic about Challenge Competitors using proper technique. We’re very proud of our record- one of the safest sports out there.

The Biomechanics of lifting and dragging with a neutral spine and in flexion:

The strategy of lifting with the spine in flexion increases the effects of shear loading on the spine and increases the chance of injury. The fully flexed spine shows myo-electric silence in back extensor muscles and strained posterior passive tissues with high shearing forces on the lumbar spine. A neutral spine (standing tall, shoulders back lumbar curve in place) recruits the pars lumborum muscle groups to support the reaction shear and reduces total joint shear (1).  A great example of this posture is demonstrated in the CrossFit article (Brandon Cunningham, dummy rescue). As a result of lifting and dragging in this posture the extensor muscles appear to contribute to the posterior shear force that supports the anterior shear action on the upper body so that the shear forces are reduced from 1000N (Newtons ≈ 224 lb.) to 200N (approximately 50 lb.).

When lifting with the torso flexing about the hips with a neutral spine (think of the hip as a hinge) in contrast to flexion of the spine, thereby reducing the risk of injury.

The fully flexed spine is weaker than one that is moderately flexed (2).

Posture coupled with the required muscular strength and endurance is paramount when lifting and dragging to avoid injury and possible spine buckling. In addition proper training will help to decrease errors in motor patterns that may cause injury.

This is why we exercise our prerogative to intervene when we observe unsafe practices and stop Competitors from hurting themselves. 

1.   McGill, S.M. Journal of Biomechanics. 30, (5) 1997.
2.   Adams et. al. Clinical. Biomechanics. 1994 9: 5-14

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