The plank is a simple exercise commonly used to stabilize the body. However, it’s also easy to progress beyond it pretty quickly. In a recent study in the Journal of Strength and Conditioning Research, a suspension trainer was used as a possible method of increasing the effectiveness of the plank.
In the study, the researchers used several plank variations to test the effect on four muscles: the serratus anterior, the rectus femoris, the external obliques, and the rectus abdominis. They used four plank variations:
- A standard plank with the elbows on the floor
- A plank with the arms suspended in a TRX suspension trainer
- A plank with the feet were suspended in a TRX suspension trainer
- A plank with both arms and feet suspended
For each plank variation they used electromyography to determine muscle activation.
Effects by Muscle Group
The serratus anterior, which is the muscle that you’ll find along your ribs under the outer edge of your pecs, helps stabilize the shoulders by bringing them forward. It also assists in breathing. The serratus was worked the hardest in the position where the legs were suspended.
The rectus femoris is the central muscle of the quadriceps. It flexes the hips and extends the knee. This muscle wasn’t worked particularly hard, but hit its peak when the arms were suspended in the plank.
The external obliques were worked harder when the arms were suspended, but this may be due to the plank being performed on the elbows. It seems like this condition would create a greater potential for rotational instability. Since the legs are longer than the arms, it makes sense that the variations that emphasized the legs being wider or staggered would prove to work the obliques more, since the obliques would have a greater need to resist rotation.
Finally, the rectus abdominis, which is the muscle most people mean when they say “abs,” was hit the hardest when the arms were in the suspension trainer, as well as when both arms and legs were in. The two conditions were no different in terms of muscle activation.
The condition in which the arms were suspended was superior for every muscle tested except for the serratus. This could be due to the suspension trainer elevating the lower body and thus providing more resistance to the serratus. It could also be because the serratus muscle controls the shoulder girdle, and is better able to activate and exert force when stabilized, which is its primary function anyway. Destabilizing the lower body allows the serratus to perform its primary function of stabilizing the shoulders.
The muscle that was worked most substantially during this test, regardless of the plank variation, was the rectus abdominis. The rectus abdominis exceeded fifty percent of its maximal voluntary contraction during the arms-in and arms-and-legs suspended conditions. No other muscle group attained that level of activation in any condition.
It seems that the plank, especially a suspended plank, is a great exercise for working the abs, and particularly for increasing endurance in the ab muscles. If you’re looking to increase the intensity of the plank for the abs, try suspending your arms and save yourself time and the funny looks you might get by putting your feet in there, too. If you want to work the other muscles tested in this study, look elsewhere.
1. Jeannette Byrne, et. al., “The Effect of Using a Suspension Training System on Muscle Activation During the Performance of a Front Plank Exercise,” Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000510
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