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NCT Number: NCT07129200

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

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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Key information

Conditions

Caffeine Thermoregulation

Age range

18 year–45 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Healthy trained runners

Exclusion criteria

-

Treatment and study plan

Hot environment

Other

Hot environment of 35 degrees Celsius

Thermoneutral environment

Other

Thermoneutral environment of 18 degrees Celsius

Primary outcomes

  1. Blood lactate concentration

    Time frame: 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.

  2. Heart rate

    Time frame: 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.

  3. Rating of perceived exertion

    Time frame: 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.

  4. Oxygen uptake

    Time frame: 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.

  5. Time trial performance

    Time frame: From baseline to completion, up to 31 days

    Change from baseline in distance covered during a 30 minute time trial on a treadmill.

Study contacts

Contact information is provided by the study sponsor or research team.

Mark Glaister

CONTACT

[email protected]

+447957616552

Sponsors and collaborators

Lead sponsor

St. Mary's University, Twickenham

Other

Registry information

Official study title

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

Important dates

Study start
2025
Primary completion
2026
Study completion
2026
First posted
Aug 19, 2025
Registry last updated
Aug 19, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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