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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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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Caffeine | Experimental | 5 mg/kg dose of caffeine (in pill form) |
|
| Placebo | Placebo Comparator | 5 mg/kg dose of placebo (maltodextrin - in pill form) |
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| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Hot environment | Other | Hot environment of 35 degrees Celsius |
| |
| Measure | Description | Time Frame |
|---|---|---|
| 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 |
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Inclusion Criteria:
Exclusion Criteria:
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| Name | Role | Phone | Extension | |
|---|---|---|---|---|
| Mark Glaister | Contact | +447957616552 | mark.glaister@stmarys.ac.uk |
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| Thermoneutral environment |
| Other |
Thermoneutral environment of 18 degrees Celsius |
|