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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
DOUBLE
Enrollment
15
Hot environment of 35 degrees Celsius
Thermoneutral environment of 18 degrees Celsius
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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: 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.
Time frame: From baseline to completion, up to 31 days
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