Understanding the Biering-Sørensen test: contributors to extensor endurance in young adults with and without low back pain.

Impaired paraspinal muscle endurance may be a contributor to persistent low back pain (LBP) and is frequently assessed using a single repetition of the Biering-Sørensen test. The aim of this study was to investigate how Sørensen test duration, and muscle fatigability, are affected by multiple repetitions of the test, and to determine predictors of Sørensen test duration in young, active adults with and without a history of LBP. Sixty-four individuals participated; 41 had a greater than one-year history of LBP symptoms. Participants performed 3 repetitions of the Sørensen test while electromyography (EMG) data were collected from the lumbar and thoracic paraspinals and the hamstrings. Muscle fatigability was quantified as the slope of the change in median frequency of the EMG signal over time. Duration of the test decreased across repetitions for both groups and was significantly less for the 2 nd and 3 rd repetitions in individuals with LBP. For all three muscles, fatigability increased across repetitions, but did not differ between groups. In individuals without LBP, fatigability of the lumbar paraspinals was the best predictor of test duration. In individuals with LBP, Sørensen test duration was predicted by fatigability of the thoracic paraspinals and hamstrings. Our findings demonstrate that it is necessary to amplify the difficulty of the Sørensen test to fully elucidate impairments in young adults with LBP. Training or rehabilitation programs aiming to improve lumbar paraspinal endurance in individuals with LBP should account for the endurance of other synergist muscle groups during endurance exercise.