ABDOMINAL MUSCLE ACTIVATION IN TWO TRUNK-CURL TESTS

INTRODUCTION Trunk-curl exercises have been advocated as the safest and most effective exercises for the abdominal muscles. Trunk-curl tests of abdominal endurance have begun to replace the bent-knee sit-up as the muscular endurance measures in health-related fitness batteries. The purpose of this study was to compare the abdominal muscle activation in two current trunk-curl tests of abdominal endurance. METHODS Twenty-three subjects (12 female and 11 male) between 19 and 24 years of age volunteered and gave informed consent for the study. Electromyographic activity of the right rectus abdominis (RA) and the left external oblique (EO) were recorded with surface electrodes (Noraxon Myosystem 2000) as the subjects performed the bench trunk-curl (Knudson & Johnston, 1995), the modified curl-up (CIAR, 1992), and two maximal voluntary contractions (MVC). Trunk motion was measured with a Penny & Giles M180 electrogoniometer attached to the lateral illiac crest and ribs. EMG and goniometer data were A/D converted at 1000 Hz and stored on disk. Curl-up tests were performed to a cadence of 20 repetitions per minute. Mean rectified EMG of the RA and EO were calculated during the first 500 ms of the concentric phase for six repetitions of each trunk-curl for each subject. Subject mean RA and EO EMG were expressed as a percentage of the maximum rectified EMG in the MVC's. Mean normalized EMG of the RA and EO were compared across trunk-curls with dependent t-tests. Statistical significance was accepted at p < 0.05. RESULTS AND CONCLUSIONS - There were no significant differences in RA and EO activation between the two trunk-curl tests. Mean normalized activation of the RA and EO were between 10.9 and 14.2% of MVC. This activation was slightly smaller than previous EMG research on sit-up/curl-ups (Ekholm, Arborelius, & Fahlcrantz, 1979). Each subject showed a consistent response of the two abdominal muscles to the trunk-curl tests, but there were between subject differences in abdominal muscle activation across tests. Most subjects (70% EO and 61% RA) had greater abdominal muscle activation in the BTC compared to the MTC. The n o d variability of abdominal muscle activation (Ekholm et al., 1979; Gilleard & Brown, 1994) could account for the no significant difference in mean activation of the RA and EO across trunk-curl tests. REFERENCES Cooper Institute for Aerobic Research. (1992). The prudential fitness grarn: test administration manual. Dallas, TX: CIAR. Ekholm, J., Arborelius, E., & Fahlcrantz, A. (1979). Activation of abdominal muscles during some physiotherapeutic exercises. ScandinavianJournal of Rehabilitation Medicine, 11,75-84. Gilleard, W., & Brown, J. (1994). An electromyographic validationof an abdominal muscle test. Archives of Physical Medicine and Rehabilitation, 75,1002- 1007. Knudson, D., & Johnston, D. (1995). Validity and reliability of a bench trunk-curl test of abdominal endurance. Journal of Strength and Conditioning Research, 9, 165-169