Microvascularity of the lumbar erector spinae muscle during sustained prone trunk extension test.

This study evaluated the reliability of oxygenation and blood volume responses, from the right erector spinae in twenty two healthy men and women, during static prone trunk extension on two separate days. Near-infrared spectroscopy (NIRS)-derived physiological change for oxygenation was calculated as the difference between the 'baseline' before the start of the trunk extension and 'minimum' at the point of volitional exhaustion. The physiological change for blood volume was calculated as the difference between the 'baseline' value and 'maximum' at the point of volitional exhaustion. Test-retest reliability, based on the intraclass correlation coefficients for the physiological change were: oxygenation--men: +0.60 versus women: +0.37; blood volume--men: +0.93 versus women: +0.59, respectively. Results suggest that NIRS-derived blood volume measurements were more reliable than the oxygenation responses. The most interesting observation of the study was the hyperemia in blood volume responses with a parallel decrease in oxygenation as participants continued the test until volitional exhaustion. Such an increase in muscle blood volume contradicts the theory that sufficient occlusion of blood flow to the lumbar muscle region is possible with static trunk extension resulting in muscle fatigue.