JUSTICE INSTITUTE OF BRITISH COLUMBIA EMG Activity of the Trunk Stabilizers During Stable and Unstable Environments Elliott, B, Gaetz, M. and Anderson, G. Training the core muscles of the trunk has application in personal training, rehabilitation and injury prevention. Training to enhance the functioning of the core muscles has been a “hot topic” of late, with the introduction of many pieces of apparatus to enhance the core muscle activation during exercise. The purpose of this study was to quantify the core muscle activation during exercises performed on various commercially available apparati that introduce an unstable training surface — the BOSU and Stability balls. The hypothesis was that there would be greater core muscle activation during exercises performed on unstable surfaces. Methods: Fifteen highly trained conditioning coaches performed 5 exercises (bridge, bridge (one leg), side bridge, curl up and the superman) on a stable surface (the floor), and two unstable surfaces (BOSU dome and Stability ball). Surface electrode electromyography was recorded over the Rectus Abdominus, Erector Spinae, and Internal Oblique muscle groups. A root mean square of the EMG was calculated for each muscle and each exercise condition. Data were analysed using a Univariant General Linear Model ANOVA, with Boneferroni post-hoc comparisons. Significance was set at the P≤0.05 level. Results: ANOVA results indicated a significant main effects for stability and muscle. Significance during stable and unstable exercise was found during the side bridge exercise only. Muscle activity within exercises was significantly different for all exercises but the curl up. The erector spinae showed greatest activation during both the two foot and one foot supported bridge, whereas the internal obliques were the most active during the side bridge. During the superman the erector spinae was the dominant muscle during stable conditions while the internal obliques were dominant during the unstable exercise. When comparing the 5 exercises, the curl up was the exercise that maximally activated the muscles of the trunk. Discussion: The present hypothesis could not be supported for any of the exercises except the side bridge. No significant differences were found between stable and unstable conditions using the bridge, single leg bridge, curl up or superman exercises. However, while not significant there was a trend with muscle activation being higher for most muscles during exercise performed on unstable surfaces. The use of highly trained conditioning coaches may explain these results. These individuals routinely “set the core” by activating the core muscles during most exercises. Setting the core increases muscle activation during exercises performed on a stable surface, reducing the difference we might expect to see in a general population. It is hypothesized that significant differences in muscle activation would be seen across exercises performed on stable and unstable surfaces when using an untrained population, or those that are not accustomed to instability training. The exercise with the greatest core muscle activation was the curl up to 45° of trunk flexion in both the stable or unstable environments. This was, however, the only dynamic exercise and this result should be expected. The side bridge was the only exercise to show a significant stability effect. This corresponds to that exercise which the subjects found most challenging in the unstable environment and probably accounts for the significant increase in muscle activation. Conclusion: Increased EMG activation of core trunk stabilizers using unstable surfaces was observed for the side bridge only. An non-significant increase in core stabilizer EMG observed during exercises performed on an unstable surface. While studies have demonstrated a significant affect using a stability ball in the past, the present study was unable to duplicate this finding in highly trained conditioning coaches. Significance was only found in that exercise that was found to be most challenging. For this reason it is hypothesized that instability training may be beneficial in those with little previous exposure to training on unstable surfaces.. Acknowledgement: This study was supported by the University of the Fraser Valley Condition Stable/Unstable Muscle Significance Most active Muscle Bridge Not significantSignificantErector spinae Bridge-1 foot Not significantSignificantErector spinae Side bridge Significant Internal obliques Curl-up Not significant N/A Superman Not significantSignificantErector spinae Exercise 1 – Bridge Exercise 2 - Bridge, 1 Foot Exercise 3 - Side Bridge Exercise 4 - Curl up Exercise 5 - Superman Table 1: Significance of results