Core Muscle Activation During Unstable Overhead Squat Using a Water-Filled Training Tube

Abstract

PURPOSE:Stability and balance are essential components for functional movement. While these components are often developed by exercising on unstable surfaces, another alternative is to use an unstable implement. The purpose of this study was to use a novel water-filled implement (“slosh tube”) to assess the degree of muscle instability created during an overhead squat. METHODS: Eight men (age= 20.1 ± 1.0y, ht=179.8 ± 4.8cm, mass= 89.2 ± 6.9kg) completed three 30s trials of an overhead squat using an 11.4 kg tube that was partially filled with water. A central valve allowed three conditions of water movement: 50% open, 100% open, and a stable(S), closed valve setting. Subjects completed 8-10 repetitions within each condition using a counter-balanced design. Muscle activation was assessed on the right side, with passive EMG electrodes placed over the belly of the vastus lateralis (VLAT), deltoid, rectus abdominus (AB), and paraspinal muscles. Integrated EMG was measured for each repetition and converted to a %MVC for each muscle. Instability was determined using the natural log of the coefficient of variation across repetitions. A two way repeated measures ANOVA across (contraction, condition) was used to examine concentric and eccentric contractions in each muscle. %MVC was also assessed. RESULTS:No significant instability was seen in any muscles for both CON and ECC. LnCV ranged from 3.0-3.5. Percent MVC activated was significantly greater for the Paraspinal muscle (CON= 53.6 ± 7.4, ECC = 45.1± 9.7%) and VLAT (CON= 332.3 ± 147.5, ECC= 288.8 ± 114.5) but not for the AB (CON= 10.6 ± 5.1, ECC= 9.2 ± 4.6) or the Deltoid ( CON= 41.3 ± 19.4, ECC = 39.7 ± 17.7) CONCLUSIONS: We conclude that the overhead squat using an unstable, water-filled tube maintains deltoid and abdominal muscle activation throughout the squat, but does not induce activation instability across the four muscles studied.