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Quantification of the Differences in Electromyographic Activity Magnitude Between the Upper and Lower Portions of the Rectus Abdominis Muscle During Selected Trunk Exercises

GJ Lehman, MSc, is Clinic Scientist, University of Waterloo-Canadian Memorial Chiropractic College (UW-CMCC) Research Clinic, Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada
SM McGill, PhD, is Professor of Spine Biomechanics, Faculty of Applied Health Sciences, Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.

Address all correspondence to Dr McGill

Background and Purpose. Controversy exists around exercises and clinical tests that attempt to differentially activate the upper or lower portions of the rectus abdominis muscle. The purpose of this study was to assess the activation of the upper and lower portions of the rectus abdominis muscle during a variety of abdominal muscle contractions. Subjects. Subjects (N=11) were selected from a university population for athletic ability and low subcutaneous fat to optimize electromyographic (EMG) signal collection. Methods. Controlling for spine curvature, range of motion, and posture (and, therefore, muscle length), EMG activity of the external oblique muscle and upper and lower portions of rectus abdominis muscle was measured during the isometric portion of curl-ups, abdominal muscle lifts, leg raises, and restricted or attempted leg raises and curl-ups. A one-way repeated-measures analysis of variance was used to test for differences in activity between exercises in the external oblique and rectus abdominis muscles as well as between the portions of the rectus abdominis muscle. Results. No differences in muscle activity were found between the upper and lower portions of the rectus abdominis muscle within and between exercises. External oblique muscle activity, however, showed differences between exercises. Discussion and Conclusion. Normalizing the EMG signal led the authors to believe that the differences between the portions of the rectus abdominis muscle are small and may lack clinical or therapeutic relevance.

Key Words: Electromyography • Exercise therapy • Low back pain • Rectus abdominis muscle

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