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

NCT07129200 | Not Yet Recruiting

• 1 other identifier: SMU_ETHICS_2024-25_1111
• Study Type: interventional
• Target: 15
• Locations: 0 countries
• Sites: N/A

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.

Conditions

Caffeine; Thermoregulation

Keywords

caffeine; thermoregulation; time trial; exercise physiology

Outcome Measures

Primary Outcomes (5)

• Blood lactate concentration

  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.

  From baseline to completion, up to 31 days

• Heart rate

  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.

  From baseline to completion, up to 31 days

• Rating of perceived exertion

  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.

  From baseline to completion, up to 31 days

• Oxygen uptake

  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.

  From baseline to completion, up to 31 days

• Time trial performance

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

  From baseline to completion, up to 31 days

Study Arms (2)

Caffeine

EXPERIMENTAL

5 mg/kg dose of caffeine (in pill form)

Other: Hot environment; Other: Thermoneutral environment

Placebo

PLACEBO COMPARATOR

5 mg/kg dose of placebo (maltodextrin - in pill form)

Other: Hot environment; Other: Thermoneutral environment

Interventions

Hot environment OTHER

Hot environment of 35 degrees Celsius

Caffeine; Placebo

Thermoneutral environment OTHER

Thermoneutral environment of 18 degrees Celsius

Caffeine; Placebo

Eligibility Criteria

• Age: 18 Years - 45 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Healthy trained runners

Sponsors & Collaborators

• St. Mary's University, Twickenham: lead

Central Study Contacts

Mark Glaister

CONTACT

+447957616552; mark.glaister@stmarys.ac.uk

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: DOUBLE
• Who Masked: PARTICIPANT, INVESTIGATOR
• Purpose: BASIC SCIENCE
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: August 12, 2025
• First Posted: August 19, 2025
• Study Start: August 22, 2025
• Primary Completion: April 30, 2026
• Study Completion (Estimated): June 30, 2026
• Last Updated: August 19, 2025

Record last verified: 2025-08