Not All Instability Training Devices Enhance Muscle Activation in Highly Resistance-Trained Individuals

Abstract

The objective of this study was to measure the electromyographic (EMG) activity of the soleus, bicep femoris, rectus femoris, lower abdominal, and lumbosacral erector spinae (LSES) muscles with a variety of (a) instability devices, (b) stable and unstable (Dyna Disc) exercises, and (c) a fatiguing exercise in 16 highly conditioned individuals. The device protocol had participants assume standing and squatting postures while balancing on a variety of unstable platforms (Dyna Disc, BOSU ball, wobble board, and a Swiss ball) and a stable floor. The exercise protocol had subjects performing, static front lunges, static side lunges, 1-leg hip extensions, 1-leg reaches, and calf raises on a floor or an unstable Dyna Disc. For the fatigue experiment, a wall sit position was undertaken under stable and unstable (BOSU ball) conditions. Results for the device experiment demonstrated increased activity for all muscles when standing on a Swiss ball and all muscles other than the rectus femoris when standing on a wobble board. Only lower abdominals and soleus EMG activity increased while squatting on a Swiss ball and wobble board. Devices such as the Dyna Disc and BOSU ball did not exhibit significant differences in muscle activation under any conditions, except the LSES in the standing Dyna Disc conditions. During the exercise protocol, there were no significant changes in muscle activity between stable and unstable (Dyna Disc) conditions. With the fatigue protocol, soleus EMG activity was 51% greater with a stable base. These results indicate that the use of moderately unstable training devices (i.e., Dyna Disc, BOSU ball) did not provide sufficient challenges to the neuromuscular system in highly resistance-trained individuals. Since highly trained individuals may already possess enhanced stability from the use of dynamic free weights, a greater degree of instability may be necessary.