3-DIMENSIONAL MOTION ANALYSIS AND POSTERIOR ANNULUS PRESSURE MEASUREMENT OF THE LUMBAR SPINE DURING ‘FREE SQUAT’ WEIGHT LIFT TRAINING

Abstract

Hypothesis: Athletes significantly alter their lumbar spinal motion when performing squat lifting at heavy weights. This altered motion effects a change in pressure in the posterior annulus of lumbar discs.

Study Design:

1. 3-D motion analysis of lumbar spinal motion in athletes, during squat weight lifting.

2. Pressure measurement of the posterior annulus following the motion analysis study.

Methods: 48 athletes performed 6 lifts at 40% maximum, 4 lifts at 60% max and 2 lifts at 80% max. 3-D motion analysis system, measured lumbar spine motion. Exercise performed as a ‘free’ squat and repeated with a weight lifting support belt.

4 cadaveric sheep spinal motion segments mounted in purpose built jig, replicating angulation seen in the in vivo motion study. These samples were then fixed to a tension/compression loading frame, replicating the forces seen in the in vivo study. Pressure measurement was achieved using a Flexiforce single element force sensor strip, positioned at the posterior annulus.

Posterior annulus pressure was measured during axial compression and on compression with the specimen fixed at 3° of extension.

Results:

1. Significant decrease (p< 0.05) in flexion in all groups when lifting at 40% max was compared with lifting at 60% and 80% of max. Flexion from calibrated zero point ranged from 24.7° (40% group), to 6.8° (80% group). A progressively significant increase (p< 0.05) seen in extension in groups studied when lifting at 40% max was compared with lifting at 60% and 80% max lift. Extension from a calibrated zero point ranged from − 1.5° (40% group), to − 20.3° (80% group). No statistically significant difference found between motion seen when performing the exercise as a ‘free’ squat or when lifting using a support belt in any group studied.

2. Initial uniform rise in measured pressure readings to a pressure of 350–400N, in the axially loaded and extension loaded specimens. Pressure experienced by the axially loaded group then gradually dropped below the pressure exerted by the loading frame, while the pressure experienced in the posterior annulus of the extension loaded specimens progressively increased.

Comparing axially loaded specimens with specimens loaded in extension, there was an average increase in pressure of 36.4% in the posterior annulus, when the spine was loaded in 3° of extension at a pressure equivalent to the 80% lift in the in vivo motion study, in comparison to axial loading.

Conclusions: Squat weight lifting at heavier weights, causes athletes to lift at a progressively greater degree of extension. The use of a weight lifting support belt does not significantly alter spinal motion during lifting. The increased extension at heavier weights results in a stress concentration in the posterior annulus of lumbar discs.