Thermoregulatory Strain and Sleep Responses Across 14 Stages of the Dakar Rally

BackgroundMultistage desert rally competitions combine prolonged environmental heat exposure, mechanical workload, altitude exposure, and restricted recovery, potentially increasing thermal and sleep-related strain. However, integrated field data collected during authentic competition remain limited.MethodsForty-six competitors (44 males, 2 females) participating in the 2018 Dakar Rally were monitored across 14 stages performed in South America under hot desert conditions. Gastrointestinal core temperature, in-vehicle microclimate temperature, actigraphy-derived sleep parameters, and perceptual measures were collected during competition. A total of 204 in-vehicle temperature recordings, 122 core temperature profiles, 131 questionnaires, and 36 nights of actigraphy were analyzed.ResultsStages were prolonged (623±206 km; 9 h 56 min ± 4 h 05 min) and environmentally variable, with 43±31% sand sections and 47% of stages exceeding 2500 m altitude. In-vehicle temperatures exceeded 50°C across all vehicle categories. Mean peak gastrointestinal core temperature reached 38.3±0.4°C; approximately one third of recorded values exceeded 38.5°C, and values ≥39°C were observed. Terrain difficulty was positively associated with peak core temperature, whereas stage duration showed weaker associations. In contrast, total sleep time and low-activity sleep were negatively associated with stage duration and altitude, largely due to earlier wake-up times. Reduced sleep duration was associated with daytime sleepiness.ConclusionsThermoregulatory strain and sleep restriction during prolonged desert rally competition appear driven by distinct operational determinants: terrain difficulty for heat strain and logistical scheduling constraints for sleep loss. Ecological physiologic monitoring may help inform medical oversight strategies in extreme motorsport.