SPECTRAL AND TEMPORAL RESPONSES OF TRUNK EXTENSOR ELECTROMYOGRAPHY TOAN ISOMETRIC ENDURANCE TEST

Study Design. This study investigated the effect oi trunk extensor mus cle location on the spectral and temporal electromyographic activity o f the muscles during a fatiguing isometric extension of the torso agai nst gravity. Objectives. To determine the spectral responses of the tr unk extensor muscles at more locations than have been studied previous ly, to determine if fatigue in the knee flexors limits this test, and to quantify the recruitment patterns of the trunk extensor muscles in a group of healthy subjects. Summary of Background Data. Isometric end urance tests appear to have more value than strength tests in predicti ng the occurrence of low back pain. Electromyographic activity of trun k extensor muscles during these tests may provide clues to the etiolog y of neuromuscular-based low back pain, Spectral electromyographic mea sures appear to be successful discriminators between low back pain pat ient and normal populations, although which muscles provide the best i nformation is unclear. likewise, the recruitment patterns of the trunk extensors during fatiguing isometric tasks is not well quantified. Me thods. Ten healthy men performed an isometric trunk endurance test, Su rface electromyography was recorded from the erector spinae medially a nd laterally at vertebral levels of L1 and L3, medially at L5, and fro m the biceps femoris and gastrocnemius. Spectral parameters were calcu lated from the Fast Fourier Transform, and temporal parameters were ca lculated from the root mean square of the raw data. Linear regression was used to determine their responses as a function of time. Results. There was a significant effect of vertebral level and medial-lateral l ocation on the initial median frequency and linear slope of the median frequency regressions. No significant evidence of fatigue in the lowe r extremities was observed. For most subjects, the temporal response o f the surface electromyography was parabolic (concave-down), peaking a t 30-50% of the endurance time.Conclusion. Establishment of which musc le locations provide the best information and knowledge of the recruit ment patterns are essential for the development of clinical diagnostic procedures and rehabilitation protocols.