The Effects of Caffeine on Exercise Physiology and Time-trial Performance in a Hot Environment

NCT07129200 — Not applicable, Not yet recruiting, 15 participants, St. Mary's University, Twickenham

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The Effects of Caffeine Supplementation on Exercise Physiology and Time-trial Performance in a Hot Environment

Registry	NCT07129200
Status	Not yet recruiting
Phase	Not applicable
Study type	Interventional; randomized, crossover, masking: double, basic science
Enrollment	15 (Estimated)
Sponsor	St. Mary's University, Twickenham (Other)
Conditions	Caffeine, Thermoregulation
Interventions	Hot environment, Thermoneutral environment (Other)
Dates	start 2025-08-22 (estimated), primary completion 2026-04-30 (estimated), completion 2026-06-30 (estimated), first posted 2025-08-19, last updated 2025-08-19

-Summary

Maintaining a stable core temperature is vital for physiological function; yet, exercise in heat can be problematic, and there is risk of exertional heat-related illness (Flouris \& Schlader, 2015; Leyk et al., 2019; Périard et al., 2021; Tyler et al., 2016; Veltmeijer et al., 2015). While aerobic fitness improves heat tolerance (Alhadad et al., 2019), strategies like acclimation and pre-cooling also mitigate heat stress (Casadio et al., 2016; Lorenzo et al., 2010; Ross et al., 2013; Siegel et al., 2010). Caffeine, an ergogenic aid (Del Corso et al., 2011; John et al., 2024), is known to enhance performance via adenosine antagonism and increased catecholamines in normothermic environments (Fredholm et al., 1999; Graham \& Spriet, 1991). However, effects in heat are inconsistent (Ganio et al., 2009; Zhang et al., 2014), possibly due to caffeine reducing the ability to thermoregulate effectively. Therefore, the aim of this study is to investigate the effects of a moderate dose of caffeine (5 mg/kg) on thermoregulation during a 30-minute running time trial in 35°C heat.

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+Arms and interventions

Arm	Type	Interventions	Description
Caffeine	Experimental	Other: Hot environment; Other: Thermoneutral environment	5 mg/kg dose of caffeine (in pill form)
Placebo	Placebo comparator	Other: Hot environment; Other: Thermoneutral environment	5 mg/kg dose of placebo (maltodextrin - in pill form)

Hot environment (Other): Hot environment of 35 degrees Celsius
Thermoneutral environment (Other): Thermoneutral environment of 18 degrees Celsius

+Outcome measures

Primary outcomes

Blood lactate concentration [From baseline to completion, up to 31 days]: Change from baseline in blood lactate concentration measured at rest and at five different exercise intensities (65, 70, 75, 80, and 85% percent of maximal oxygen uptake) on a treadmill.
Heart rate [From baseline to completion, up to 31 days]: Change from baseline in heart rate measured at rest and at five different exercise intensities (65, 70, 75, 80, and 85% percent of maximal oxygen uptake) on a treadmill.
Rating of perceived exertion [From baseline to completion, up to 31 days]: Change from baseline in rating of perceived exertion measured (using the 6-20 Borg scale) at five different exercise intensities (65, 70, 75, 80, and 85% percent of maximal oxygen uptake) on a treadmill.
Oxygen uptake [From baseline to completion, up to 31 days]: Change from baseline in oxygen uptake measured at five different exercise intensities (65, 70, 75, 80, and 85% percent of maximal oxygen uptake) on a treadmill.
Time trial performance [From baseline to completion, up to 31 days]: Change from baseline in distance covered during a 30 minute time trial on a treadmill.

+Eligibility

Sex: Male, ages: 18 Years to 45 Years, accepts healthy volunteers

Inclusion Criteria:

* Healthy trained runners

Exclusion Criteria:

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