Faculty Scholarly Dissemination Grants


Core Muscle Activation During Unstable Bicep Curl Using a Water-Filled Training Tube


Movement Science Department


College of Liberal Arts and Sciences

Date Range



Life Sciences


PURPOSE: Stability and balance are essential components for functional movement. These components may developed by training with unstable surfaces, or unstable loads. The purpose of this study was to use a novel unstable implement (slosh tube) and assess the degree of muscle instability created during a bicep curl. METHODS: Ten men (age= 21+ 1.6y, ht=180.0 + 3.3cm, mass= 87.4 + 15.0kg) and ten women (age= 19.6+ 1.3y, ht=161.4 + 12.0cm, mass= 61.2 + 7.4kg) completed three, 30s trials of a bicep curl using an 11.4 kg tube partially filled with water. A central valve allowed three conditions of water movement: 50% open, 100% open, and a balanced, closed valve setting. Subjects completed 8-10 repetitions within each condition (1.5s per rep) using a counter-balanced design. Muscle activation was assessed on the right side, using bipolar surface electrodes placed over the belly of the bicep, deltoid, rectus abdominus and paraspinal muscles. Integrated EMG was measured for each repetition and converted to a %MVC for each muscle. Instability was determined using the coefficient of variation across repetitions. A two way repeated measures ANOVA (gender, condition, gender x condition) with post hoc t-tests was used to examine concentric contractions only. RESULTS: Significant instability was seen in the paraspinal muscles for both genders at the 50% (CV= 26.5 + 14.5) and 100% (CV= 27.1 + 9.9) condition compared to stable (CV= 15.0 + 9.1). Across all subjects the deltoid showed greatest instability at the 100% open setting (CV= 38.5 + 23.2) compared to stable (CV= 21.0 + 7.5). For the bicep, men showed greater overall instability (CV= 30.9 + 17.0) compared to women (CV= 22.9 + 8.4). There were no differences in abdominal activation in any condition. Percent MVC activated was significantly greater for women for the bicep (50= 97.7 + 57.6, 100= 88.1 + 55.6, stable= 87.0 + 50.1) and paraspinal (50= 36.7 + 22.3, 100= 47.5 + 29.0, stable= 38.6 + 23.9) compared to men (bicep50= 39.5 + 17.0, 100= 38.3 + 18.3, stable= 31.8 + 11.1) (paraspinal 50= 15.1 + 10.0, 100= 16.2 + 8.8, stable= 14.3 + 9.6). No differences were seen for deltoid or abdominal. CONCLUSION: We conclude that a bicep curl using an unstable implement utilizing water inertia causes increased paraspinal and deltoid instability in men and women, with additional instability in the bicep for men.

Conference Name

American College of Sports Medicine Annual Meeting

Conference Location

San Diego, CA

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