Multiple measures of muscle function influence Sorensen Test performance in individuals with recurrent low back pain

BACKGROUND: Sorensen Test time-to-task-failure (TTF) predicts several low back pain (LBP) clinical outcomes, including recurrence. Because the test is described as a measure of trunk extensor (TE) muscle endurance, LBP rehabilitation programs often emphasize endurance training, but the direct role of TE muscle function on Sorensen Test-TTF remains unclear. OBJECTIVE: To assess the discriminative and associative properties of multiple markers of isolated TE performance with regard to Sorensen Test-TTF in individuals with recurrent LBP. METHOD: Secondary analysis of baseline measures from participants in a registered (NCT02308189) trial (10 men; 20 women) was performed. Participants were classified by Sorensen Test-TTF as high, moderate or low risk for subsequent LBP episodes, and compared to determine if classification could discriminate differences in TE function. Correlations between Sorensen Test-TTF and isolated TE performance, anthropometrics and disability were investigated. RESULTS: Individuals at risk of subsequent LBP episodes had greater perceived disability and fat mass/TE strength ratios (P⩽ 0.05) than those not at risk. Modest, significant (r= 0.36-0.42, P⩽ 0.05) associations were found between Sorensen Test-TTF, TE endurance and fat mass/TE strength. Exploratory analyses suggested possible sex-specific differences related to Sorensen Test-TTF. CONCLUSIONS: Isolated TE muscle endurance is only one of several factors with similar influence on Sorensen Test-TFF, thus LBP rehabilitation strategies should consider other factors, including TE strength, anthropometrics and perceived disability.