Muscle function and size in the lumbar spine before and after a four week exercise intervention.

BACKGROUND: Exercise of the spinal muscles is recommended for a variety of rehabilitative reasons but it is not always clear whether interventions are effective in improving the performance of the muscles or whether their benefit is elicited via other mechanisms.

OBJECTIVE: To explore the effects of an exercise intervention on the size and exercise performance of the lumbar spine extensor muscles.

METHODS: Eleven healthy participants undertook a four week programme of exercise. Magnetic resonance imaging and phosphorus spectroscopy were performed before and after the intervention to determine the time to fatigue and phosphocreatine (PCr) depletion during a muscle endurance test (modified Biering-Sørensen) together with muscle cross-sectional area (CSA).

RESULTS: The post intervention measures were significantly different to the pre-intervention results for the time to fatigue (post-pre: 20.5 ± 22.7 s (P= 0.014)) and PCr depletion both at the point of fatigue (post-pre: 9.5 ± 11.9% (P= 0.024)) and at a matched time-point (post-pre: 12.2 ± 11.9% (P= 0.007)). CSA was not significantly different in any muscle.

CONCLUSIONS: Exercise improved the performance of the trunk muscles despite no impact on CSA. This demonstrated the importance of obtaining a wide range of measures when assessing the effectiveness of exercise intervention programmes.