Study Design: Cross-sectional study. Objective: The self-reported reasons for terminating isometric back extension endurance testing and their associations with test performance and other factors were investigated to gain insight into determinants of test performance. Background: Factors limiting isometric back extension endurance performance remain unclear. Better understanding the reasons for termination of isometric extension endurance testing could provide insights into what the test actually reflects. Methods and Measures: Lifetime work, leisure activities and back pain questionnaire data, isometric back extension endurance testing (holding time, as measured in seconds), and reasons for test termination were obtained for a population-based sample of 544 working-age men. Results: The most common reason for test termination was fatigue (62.5%), followed by pain in various parts of the lower extremities (12.6% ) and back (3.2% ). A history of daily low back pain over the prior 12 months and greater pain intensity of the worst back pain episode over the same period were associated with a greater likelihood of termination due to back pain. In a regression analysis, longer holding time was associated with stopping due to fatigue rather than low back pain, with a trend of 19 seconds (95% confidence interval [CI], -2-40) longer holding time. After controlling for low back pain history, those previously involved in competitive sports were 2.6 times more likely to stop due to pain. Those with a competitive sport history had 14 seconds (95% CI, 5-23) greater holding time than those without such a history. Conclusions: Isometric back extension endurance testing is most commonly reported to be terminated due to muscle-related capacity as indicated by fatigue. Back pain is more likely to decrease performance time in men with a history of significant (frequent, intense) low back symptoms.

J Orthop Sports Phys Ther. 2005;35(7):437-442. doi:10.2519/jospt.2005.2007

Key Words: fatigue, low back pain, lumbar spine, muscle