| Summary: | <p>Abstract</p> <p>Background</p> <p>High-intensity interval training has been shown to be a time-efficient way to induce physiological adaptations similar to those of traditional endurance training. Creatine supplementation may enhance high-intensity interval training, leading to even greater physiological adaptations. The purpose of this study was to determine the effects of high-intensity interval training (HIIT) and creatine supplementation on cardiorespiratory fitness and endurance performance (maximal oxygen consumption (VO<sub>2PEAK</sub>), time-to-exhaustion (VO<sub>2PEAK</sub>TTE), ventilatory threshold (VT), and total work done (TWD)) in college-aged men.</p> <p>Methods</p> <p>Forty-three recreationally active men completed a graded exercise test to determine VO<sub>2PEAK</sub>, VO<sub>2PEAK</sub>TTE, and VT. In addition, participants completed a time to exhaustion (TTE) ride at 110% of the maximum workload reached during the graded exercise test to determine TWD (TTE (sec) × W = J). Following testing, participants were randomly assigned to one of three groups: creatine (creatine citrate) (Cr; <it>n </it>= 16), placebo (PL; <it>n </it>= 17), or control (<it>n </it>= 10) groups. The Cr and PL groups completed four weeks of HIIT prior to post-testing.</p> <p>Results</p> <p>Significant improvements in VO<sub>2PEAK </sub>and VO<sub>2PEAK</sub>TTE occurred in both training groups. Only the Cr group significantly improved VT (16% vs. 10% improvement in PL). No changes occurred in TWD in any group.</p> <p>Conclusion</p> <p>In conclusion, HIIT is an effective and time-efficient way to improve maximal endurance performance. The addition of Cr improved VT, but did not increase TWD. Therefore, 10 g of Cr per day for five days per week for four weeks does not seem to further augment maximal oxygen consumption, greater than HIIT alone; however, Cr supplementation may improve submaximal exercise performance.</p>
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