Background Currently, there are few studies on the cardiovascular and fatigue effects of commercially available energy drinks. This study investigated the effects of Monster energy drink (Monster Beverage Corporation, Corona, California), on resting heart rate (HR), heart rate variability (HRV), ride time-to-exhaustion, peak exercise HR, respiratory exchange ratio (RER), and peak rating of perceived exertion (RPE). Methods The study used a double-blind, randomized, placebo controlled, crossover design. After an 8-hr fast, 15 subjects consumed Monster Energy Drink (ED standardized to 2.0 mg * kg-1 caffeine) or a flavor-matched placebo preexercise. Resting HR and HRV were determined. After an initial submaximal workload for 30 minutes, subjects completed 10 min at 80% ventilatory threshold (VT) and rode until volitional fatigue at 100% VT. Results Resting HR was significantly different (ED: 65+/-10 bpm vs. placebo: 58+/-8 bpm, p?=?0.02), but resting HRV was not different between the energy drink and placebo trials. Ride time-to-exhaustion was not significantly different between trials (ED: 45.5+/- 9.8 vs. placebo: 43.8+/-9.3 min, p?=?0.62). No difference in peak RPE (ED: 9.1 +/- 0.5 vs. placebo: 9.0 +/- 0.8, p?=?1.00) nor peak HR (ED: 177 +/- 11 vs. placebo: 175 +/- 12, p?=?0.73) was seen. The RER at 30% of VT was significantly different (ED: 0.94 +/- 0.06 vs. placebo: 0.91 +/- 0.05, p?=?0.046), but no difference between the two conditions were seen at the other intensities. Conclusion Although preexercise ingestion of the energy drink does increase resting HR there was no alteration in HRV parameters. Ride time-to-exhaustion was not enhanced.
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