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

Not Applicable

Not yet recruiting

• Conditions: Caffeine; Thermoregulation

• Registration Number: NCT07129200
• Lead Sponsor: St. Mary's University, Twickenham

Brief 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.

Detailed Description

Not available

Study Timeline

• Status Verified: 2025-08
• Study First Submitted: 2025-08-12
• Study First Submitted QC: 2025-08-12
• Last Update Submitted: 2025-08-12
• Study First Posted: 2025-08-19
• Last Update Posted: 2025-08-19
• Study Start: 2025-08-22
• Primary Completion: 2026-04-30
• Study Completion: 2026-06-30

Recruitment & Eligibility

• Status: NOT_YET_RECRUITING
• Sex: Male
• Target Recruitment: 15

Inclusion Criteria

• Healthy trained runners

Exclusion Criteria

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: CROSSOVER

Primary Outcome Measures

Name	Time	Method
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.
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.
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.