J. Beal, E. LaRue, S. Pello, A. Woodie, W. M. Silvers

Whitworth University, Spokane, WA

Previous research has demonstrated the combine benefits of caffeine (CAF) and carbohydrates (CHO) as ergogenic aids for aerobic endurance performance. However, muscular endurance has not received much research attention in this area. PURPOSE: The purpose of this study was to determine the effects of a CAF-CHO supplement on muscular endurance performance via the YMCA bench press test (YMCA). METHODS: Twenty-two eligible participants (nm = 11; nf = 11; ht: 175.8 ± 9.3 cm; bw: 76.3 ± 12.5 kg; age: 20.2 ± 1.2 y) participated in this study. Inclusion criteria included that participants had previous weightlifting experience and consumed CAF less than three times a week. The YMCA was performed in cadence to a metronome set at 60 bpm (a repetition occurred every two beats). All participants completed the YMCA for two drink conditions: CAF-CHO (6 mg/kg bw caffeine + 20 g carbohydrate mixed into 16 fl oz of water) and placebo (PLA). Following drink ingestion, participants waited 45 min before performance of the YMCA. Repetitions performed to exhaustion (REPS), heart rate (HR), and rating of perceived exertion (RPE) were recorded. Dependent groups t-tests (alpha set at p ≤ 0.05) were utilized to determine statistical differences between trials. RESULTS: Significant differences were observed for REPS between drink conditions (CAF-CHO: 35.4 ± 13.1 reps vs. PLA: 32.5 ± 12.5 reps; p = 0.02). There were no significant differences between drink conditions for HR (CAF-CHO: 124.4 ± 20.5 bpm vs. PLA: 121.7 ± 20.9 bpm; p = 0.46) or RPE (CAF-CHO: 13.5 ± 1.5 vs. PLA: 13.3 ± 1.2; p = 0.32) despite trends that indicate otherwise. CONCLUSION: Under the present research conditions, the CAF-CHO supplement improved muscular endurance as measured via the YMCA. This may have been due more to the metabolic effects of carbohydrate, which presumably increased glucose availability, though that dependent variable was not measured. Under the present research conditions, HR and RPE were not affected, which previous research has shown to be influenced by caffeine. Due to the combination of small effect sizes (dHR = 0.13; dRPE = 0.15)for these dependent variables and a small sample size, the risk that a Type II error was committed is high (βHR = 0.95; βRPE = 0.95). Consequently, future research that includes a larger sample size or additional dependent variables, such as blood glucose levels, is necessary to reproduce and verify the findings in the present study.

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