outer-core-abdominal-musclesCore exercises have become popular in both fitness training and rehabilitation. The rectus abdominus and oblique muscles of the trunk are often considered part of the ‘core’ since they provide flexion, rotation, and stabilization. While flexion and rotation movements are easily created with traditional abdominal exercises such as the curl-up and trunk rotation, stabilization exercises are somewhat more controversial. Some advocate “bracing” the abdominal muscles, while others perform arm and leg movements while maintaining a stable pelvis.

While these exercises may activate the trunk stabilizers, they may not be truly exercising the muscles in the manner they function: reactive stabilization. In other words, these muscles function on a subconscious level prior to voluntary, conscious movement of the extremities to stabilize the trunk. This “reactive” stabilization provides a stable base from which we can move our extremities.

Some researchers have shown that arm movements in standing include a reactive stabilization of the trunk muscles; however, no researchers have examined the muscle activation levels during elastic-resisted arm exercises.

Researchers in South Korea wanted to assess the effect of blue Thera-Band® elastic band exercises during shoulder flexion, extension, and horizontal abduction in a seated position. 20 healthy subjects were assessed using surface EMG of the rectus abdominus, external oblique, and internal obliques.

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EMG data was collected during an isometric hold at end range during bilateral shoulder flexion, extension, and horizontal abduction. They found that activation of the rectus abdominus and obliques was significantly higher in shoulder extension and horizontal abduction than in flexion. The researchers stated that Thera-Band resisted shoulder extension and horizontal abduction “can be recommended for low back pain patients who cannot perform trunk stabilization exercises directly.” Furthermore, stroke patients with trunk muscle deficits may also benefit from this exercise. Obviously, further research should examine different muscles and exercises, as well as the effect of these exercises in patients with low back pain.

REFERENCE: Lee DK, et al. Effects of changing the resistance direction using an elastic tubing band on abdominal muscle activities during isometric upper limb exercises. J Phys Ther Sci. 2012. 24:703-706.

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