Testing isometric fatigue in the trunk muscles

Abstract

Muscle fatigue has high relevance in human performance and may contribute to the high incidence of back pain amongst athletes. However, the term fatigue is often poorly defined and is used inconsistently, frequently being interchanged with endurance. This study aimed to establish whether the Biering-Sorensen test and a test of fatigue for the abdominal muscles were effective at inducing fatigue using a well established definition. Twenty medical students were subjected to two protocols (A & B). Using a Cybex norm isokinetic dynamometer, the isometric peak torques during extension and flexion were measured before and after each protocol. Protocol A involved a 45 second maximal isometric contraction within the dynamometer while Protocol B entailed a Biering-Sorensen (submaximal) test for extension and a sit up crunch for flexion. Extension testing followed flexion testing. Significant reduction in peak mean torque occurred only in flexion for both protocols. The Biering-Sorensen test did not result in a decrease in peak torque suggesting minimal fatigue (using the definition used in this study). A weak correlation was found between the length of time the Biering-Sorensen test was held and the fatigue index. The Biering-Sorensen test does not appear to reduce maximum voluntary contraction strength and remains a test of endurance. However, a similar test for the abdominal muscles did induce fatigue. Further research is required to develop an effective protocol to assess trunk extensor fatigue.