We are starting a new weekly “Throwback Thursday” feature to the Academy Research blog. Each Thursday, I will be providing a review of relevant research prior to 2009 (per the 5-year rule!), which is actually when our blog started.

This is one of the first and most important EMG studies on the exercise ball. It was published in the Physical Therapy journal in 2000 from Stu McGill’s lab in Canada. It’s impact is in the amount of activation of the abs during a curl-up on an exercise ball compared to a stable surface, and it offers a progression of abdominal activation.


Abdominal muscle response during curl-ups on both stable and labile surfaces

The purpose of this study was to compare the electromyographic (EMG) activity of the abdominal muscles while performing curl ups on stable surfaces and labile surfaces. Eight healthy male subjects with no history of back pain performed curl-up exercises under 4 different conditions. The stable surface curl was performed on a padded bench. The three labile surfaces included (1) curl-up on an exercise ball with feet on the floor, (2) curl up on an exercise ball with feet on a bench at the same height as the ball, and (3) curl up with upper body supported by a wobble board. EMG activity was recorded from 4 different abdominal sites: upper and lower rectus abdominus, and the external and internal obliques.

exball_bridge_ab-crunch2Researchers reported that performing a curl-up on the stable bench produced the lowest amplitude of abdominal activity, while curl-up on an exercise ball with feet on the floor produced the highest amplitudes. The exercises performed on the 3 labile surfaces doubled the activity of the abdominals. Curl-up on an exercise ball with feet on a bench was comparable to performing a curl-up on the wobble board. During the exercise ball curl-up with feet on the floor, the external oblique EMG activity was 4 times more than on the stable surface. There was also significantly more activity from the lower rectus abdominus while using the exercise ball with feet on the floor compared to the other 3 exercises. This task was the most demanding in terms of maintaining whole-body stability.

In summary, this study was one of the first to quantify the EMG activity of the abdominals using an exercise ball. It demonstrated that abdominal muscle activity increases significantly when using an unsteady surface compared to a stable surface. In particular, a curl-up performed with the feet flat on the floor significantly increases lower rectus abdominus and external oblique activity. Therefore, an abdominal exercise progression can be established from curl-up on a bench → curl-up on exercise ball with feet on a bench → exercise ball with feet on floor.

REFERENCE: Vera Garcia, et al. 2000. Abdominal muscle response during curl-ups on both stable and labile surfaces. Phys Ther 80(6):564-569.

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