The Effect Of Crunch Exercise Speed On Electromyographic Activity Of Three Abdominal Muscles

Abstract

In studies using electromyography (EMG) to analyze the electrical activity of the abdominal muscles during core strengthening exercises, the data are typically collected for a fixed period of time or repetitions, early in the activity. A previous study found no significant difference in EMG activity between a 2 second and a 4 second crunch speed during this aforementioned initial phase. However, it is common practice to perform crunches to the point of fatigue, therefore making it relevant to consider the electrical activity at exhaustion. PURPOSE: To look at the influence of speed of repetitions on the electrical activity of the abdominal muscles during crunches performed to fatigue. METHODS: 10 trained, college-age male subjects (mean age = 20.8 yrs.) performed four second abdominal crunches (FS) and two second crunches (TS), in time to a metronome, to exhaustion in two separate trials. Electrical activity of the upper rectus abdominis (URA), lower rectus abdominis (LRA), and external oblique (EO) muscles were recorded using a Biopac™ bipolar electrode EMG system in which data were normalized as a percent of a maximum isometric abdominal curl against resistance. The order of trials was randomized and performed with 48 hours between trials. Data were analyzed using a 2 X 3 linear model ANOVA with a Scheffe post hoc test. RESULTS: Crunches performed at a faster speed were found to have significantly more electrical activity than slower crunches at fatigue (p< 0.01). The comparisons of the fast crunch to the slow crunch by muscle were as follows: URA, 10.65 ± 4.46 % vs. 8.04 ± 1.84 %; LRA, 11.86 ± 4.27 % vs. 8.64 ± 2.26 %; EO, 13.79 ± 3.05 % vs. 8.86 ± 3.07 %. CONCLUSION: Contrary to the findings of the previous research which only looked at the initial repetitions, a faster 2 second crunch elicits greater EMG activity than a slower 4 second crunch when completed to fatigue.