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

Impaired paraspinal muscle endurance may contribute to persistent low back pain (LBP) and is frequently assessed using a single repetition of the Biering-Sørensen test. This study investigated how Sørensen test duration, muscle activation, and muscle fatigability are affected by multiple repetitions of the test, and determined predictors of Sørensen test duration in young, active adults with and without a history of LBP. Sixty-four individuals with and without persistent LBP performed 3 repetitions of the Sørensen test. Amplitude of activation and median frequency slope (fatigability) were calculated for the lumbar and thoracic paraspinals and the hamstrings. Duration of the test was significantly less for the 2 and 3 repetitions in individuals with LBP. 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 hamstrings and amplitude of activation of the thoracic and lumbar paraspinals. Our findings demonstrate that it is necessary to amplify the difficulty of the Sørensen test to elucidate impairments in young, active adults with LBP. Training programs aiming to improve lumbar paraspinal performance in individuals with LBP should monitor performance of other synergist muscles during endurance exercise.