Purpose: Since most previous reports of EMG activation profiles from psoas and the abdominal wall have been qualitative, the objective of this work was to document myoelectric activity from these deep muscles. This knowledge is required to assist in choosing specific training exercises and for making rehabilitation decisions that require knowledge of normalized and calibrated muscle activation levels in different tasks.
Methods: Intramuscular EMG was collected from five men and three women, in whom amplitudes were normalized to maximum contraction efforts and reported over a wide variety of clinical and rehabilitation tasks. Electrodes were inserted into vertebral portions of psoas and the three layers of the abdominal wall. Normalized signal amplitudes were reported as peak levels and time histories.
Results: All forms of sit-ups activated psoas (15-35% MVC) more than the curl-up(<10%); psoas was not highly activated during barbell lifting of loads up to 100 kg (<16% MVC); psoas was most active during maximal hip flexion efforts; push-ups activated psoas up to 25% MVC. Several isometric abdominal exercises were evaluated using the criteria of maximizing abdominal activation while minimizing psoas activity: the side (bridge) support exercise proved the best training method for the abdominal wall.
Conclusions: Consideration of deep muscle activity, provided in this report, is important for choosing the most appropriate rehabilitation and training program for an individual. Specific guidance is provided for choosing the best abdominal exercise, together with activation profiles during lifting, during twisting, and during hip rotation.
Institute of Sports Science, Federal School of Sports, Magglingen, SWITZERLAND; Occupational Biomechanics and Safety Laboratories, Department of Kinesiology, University of Waterloo, N2 L 3G1, Waterloo, CANADA; Institute for Computer Science and Applied Mathematics, University of Bern, Bern, SWITZERLAND; Orthopaedic Research Laboratory, Division of Orthopaedic Surgery, McGill University, Montreal, CANADA
Submitted for publication March 1996.
Accepted for publication June 1997.
The authors thank Professor H. Hoppeler for scientific support, Maria Keiser and Michael Kientsch for technical assistance, and gratefully acknowledge the financial support of the Federal Sports School and the Federal Committee of Sports, Switzerland, and the Natural Sciences and Engineering Research Council, Canada.
Current address for Daniel Juker: Thurgauisch-Schaffhausische Höehenklinik, CH-7270, Davos-Platz, Switzerland; and for Peter Kropf: Université Laval, Dépt. d'informatique, Faculté des sciences et génie, Quebec, Canada.
Address for correspondence: Prof. S. McGill, Ph.D., Occupational Biomechanics & Safety Labs, Department of Kinesiology, University of Waterloo, Waterloo N2L 3G1, Canada.