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

The Biering-Sørensen test is commonly used to assess paraspinal muscle endurance. Research using a single repetition of the test has provided conflicting evidence for the contribution of impaired paraspinal muscle endurance to low back pain (LBP). 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 adults with and without a history of LBP. Sixty-four young individuals performed three repetitions of the Sørensen test. Amplitude of activation and median frequency slope (fatigability) were calculated for the lumbar and thoracic paraspinals and hamstrings. Duration of the test was significantly less for the 3rd repetition in individuals with LBP. In individuals without LBP, test duration was predicted by fatigability of the lumbar paraspinals. 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 reveal impairments in young, active adults with LBP. Training programs aiming to improve lumbar paraspinal performance should monitor performance of other synergist muscles during endurance exercise.