Jesse A. Stein1, Melitza R. Ramirez1, & Katie M. Heinrich1

1Kansas State University, Manhattan, Kansas

Caffeine’s ergogenic effects during endurance and high-intensity exercise are well-established. However, habitual caffeine use may diminish its ergogenic properties. Researchers have investigated high-intensity functional training (HIFT) which incorporates endurance, weightlifting, and gymnastics modalities performed at a relatively high-intensity. However, the effects on caffeine supplementation on HIFT performance remain unknown. PURPOSE: Our study aimed to determine the effects of caffeine on HIFT performance between low- and high-caffeine users. METHODS: 13 HIFT-trained men were recruited. Participants completed a 7-day caffeine recall to determine low- (<200mg/day, n=7, age=29.3±8.4 years, HIFT-experience=5.2±3.2 years, weight=86±11.3 kg) and high-caffeine users (>300mg/day, n=6, age=27.7±4.2 years, HIFT-experience=2.8±2.4 years, weight=94.5±8.5 kg). Using a double-blind, crossover design, participants were randomized to consume 5mg/kg body weight of caffeine or a placebo 60 minutes before a HIFT workout. The HIFT workout consisted of as-many-rounds-as possible in 20 minutes of 5 pull-ups, 10 push-ups, and 15 air squats (1 round = 30 repetitions). HIFT performance was determined by the absolute difference in repetitions between the caffeine and placebo conditions (HIFT performance = repetitions during caffeine – repetitions during placebo). An independent-samples t-test was used to determine the differences in HIFT performance between low- and high-caffeine users. RESULTS: Low- and high-caffeine users completed 451±91 vs. 395±95 and 501±95 vs 415±99 repetitions during the placebo and caffeine conditions, respectively. HIFT performance was not significantly different between low- and high-caffeine users (50±38 vs. 20±18 repetitions, p=0.10). CONCLUSION: Caffeine’s ergogenic effect was not significantly different between low- and high-caffeine users’ performance, suggesting a no caffeine tolerance effect. HIFT athletes may benefit from supplementing caffeine without significant impairments from high-caffeine consumption. Future investigations should determine the effects of caffeine utilizing other HIFT workouts, and consider stratifying participants by daily caffeine consumption relative to body weight.

ACKNOWLEDGEMENTS: This study was funded by the Kansas State University, College of Human Ecology.

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