Influence Of Unstable Surface (swissball) In The Muscular Activation During Isometric Bridging Exercises

Abstract

PURPOSE:The purpose of this study was to compare the intensity of EMG activation in a group of trunk muscles in two bridge exercises performed on a stable and on an unstable surface. METHODS: 35 males (age=20.9±2.5) performed Lateral Bridge (LB) and Prone Bridge (PB) in a stable (box) and unstable (swissball) surface. The duration of each exercise was 20 s. Surface EMG was recorded from upper (URA) and lower (LRA) portions of the left Rectus Abdominis, left Internal Oblique (IO), left Longissimus Thoracis (LT) and right Multifidus (MF). In each exercise the average intensity of the normalized EMG was measured during the first and final periods of 5 seconds. The analysis of variance for repeated measures (General Linear Model) was used to identify effects (p<0.05) of surface and time period of 5s in the EMG level of activation. The paired samples t-test was used to detect differences (p<0.05) between surfaces (stable and unstable) and periods of the exercise (initial and final 5s). RESULTS: In LB the muscles LRA, IO and MF showed significant higher EMG activation when the exercise was performed in the swissball compared with the stable surface. This was observed in both periods of 5s (initial and final). In both LB exercises a significant increase of the EMG activation was found from the first to the final 5s in all muscles, except the IO in the stable condition. In PB we found significant higher EMG activation in the URA and LT muscles when the exercise was performed in the swissball. However, we did not find differences in the initial period of 5s. Significant differences for the URA and LT were only found for the final period of 5s where all muscles showed higher mean EMG values in the swissball. When we compared the initial with the final period of 5s in the PB performed in the swissball, all muscles showed in the final period increase in the mean values of EMG activation but significant differences were only found for LRA and MF. When the same comparison was made for the PB performed in the stable exercise, no differences were found. CONCLUSIONS: The use of an unstable surface, the swiss ball, allowed for greater solicitation of trunk muscles during bridging exercises. However, this effect was not observed in each type of bridge exercise in all recorded muscles and it was more evident when the exercise was performed during a period of 20 seconds.