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.
Methods
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48 athletes performed 6 lifts at 40% maximum, 4 lifts at 60% maximum and 2 lifts at 80% maximum. Zebris 3-D motion analysis system used to measure lumbar spine motion. Exercise then repeated with weight lifting support belt.
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4 cadaveric sheep spinal motion segments fixed to tension/compression loading frame, allowing compression replicating the forces seen in in vivo study. Pressure measurement achieved using a Flexiforce single element force sensor strip, positioned at posterior annulus. Posterior annulus pressure measured during axial compression and on compression with specimen fixed at 3° of extension.
Results
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Significant decrease (p<0.05) seen in flexion in all groups studied when lifting at 40% maximum was compared with lifting at 60% and 80% of maximum lift. Extension from a calibrated zero point ranged in groups studied from -1.5° (40% group), to -20.3° (80% group). No statistically significant difference found between motion seen when performing exercise as ‘free’ squat or when lifting using support belt in any group.
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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.
