Electromyographic activity of the lumbar and hip extensors during dynamic trunk extension exercise

Objective: To evaluate the effects of exercise intensity and multiple sets on muscle activation patterns during trunk extension exercise. Design: Descriptive, repeated measures. Setting: University-based musculoskeletal research laboratory. Participants: Twenty volunteers recruited from a university setting. Intervention: Not applicable. Main Outcome Measures: Electromyographic activity was recorded from the L3-4 paraspinal region, gluteus maximus, and biceps femoris muscles during multiple sets of trunk extension exercise at intensities representing 40%, 50%, and 70% of peak isometric force. Results: As exercise intensity increased, the electromyographic activity of the gluteus maximus increased to a greater extent than the activity of the paraspinal region. At the 50% intensity level, biceps femoris electromyographic activity was significantly greater than the paraspinal region electromyographic activity, whereas at the 70% intensity no differences were found between muscles. During multiple sets of exercise at the same intensity a muscle by set interaction was observed. This interaction revealed that with respect to other muscle groups, the electromyographic activity of the gluteus maximus increased between sets 1 and 2, whereas electromyographic decrements occurred in the paraspinal region. During exercise at the 40% intensity level, biceps femoris electromyographic activity increased to a greater extent between sets 1 and 2 when compared with the paraspinal region. Conclusion: Exercise intensity and multiple sets result in alterations in muscle recruitment patterns of the lumbar and hip extensor muscles. These findings raise questions as to the efficacy of added loading and multiple sets during trunk extension exercise.