Evaluating the Combined Effects of Thermal Strain and a Prolonged Cognitively Demanding Task on Cognitive Performance

Introduction: Environmental heat stress can adversely affect cognitive performance, mood, and physiological responses, but the interplay between these factors during sustained cognitive tasks remains under-explored.This study aimed to identify the effects of a prolonged cognitively demanding task during thermoneutral conditions, and when combined with heat stress on cognitive performance. We hypothesised that cognitive performance following a prolonged cognitively demanding task performed while exposed to heat would be reduced. We also hypothesised that thermal and cardiovascular strain, and perceptions of thermal discomfort and fatigue would be increased while vigour would be decreased. Methods: Seven adults (3F/4M, 29±5 y; 174.4±9.4 cm; 79.9±17.2 kg; 1.9±0.3 m 2 ) completed three experimental trials in randomized order while exposed to thermoneutral (TN, 34ºC) or hot (HS, 50ºC) water circulating through a water perfused suit. Trial 1 (T1) consisted of passive rest for 90 min in a TN environment; Trial 2 (T2) consisted of 90 min of the Stroop Colour Word Test (SCWT) in 3 x 30 min blocks in a TN environment; Trial 3 (T3) consisted of 90 min of the SCWT in HS. Rectal (Trec) and mean skin temperature (Tsk), heart rate (HR), systolic (SBP) and diastolic blood pressure (DBP) were measured continuously throughout the protocol. Perceptions of thermal sensation (TS), thermal comfort (TC) and affect were obtained before and after each 30 min SCWT block. The Brunel Mood Scale (BRUMS, fatigue and vigour domains) and cognitive performance (5 min Sustained Attention Response Task (SART)) were completed pre- and post- trials. Results: The change (pre- to post-trial) for Trec (T1: +0.0±0.2ºC; T2: -0.1±0.3ºC; T3: +0.7±0.5ºC), mean skin temperature (T1: +0.5±0.5ºC; T2: +0.4±0.4ºC; T3: +3.5±1.9ºC) and HR (T1: +0±9 bpm; T2: +0±7 bpm; T3: +19±10 bpm) was significantly greater (p<0.05) in T3 compared to T1 and T2, but there were no differences in SBP or DBP (P>0.05). Average TS and TC scores were significantly higher (p<0.001) in T3 (TS: 5.8±0.7 a.u.; TC: 2.8±0.4 a.u.) compared to T1 (TS: 4.3±0.3 a.u.; TC: 1.2±0.2 a.u.) and T2 (TS: 4.5±0.4 a.u.; TC: 1.4±0.4 a.u.), indicating people felt hotter and more uncomfortable. Affect was only significantly different (p<0.001) between T1 (0.8±1.3 a.u.) and T3 (-0.9±1.8 a.u.). The change in reported fatigue was significantly greater (p<0.01) in T3 (+2.3±2.2 a.u.) compared to T1 (-0.3±1.7 a.u.), while there were no significant differences in the change in reported vigour between trials (P>0.05). Finally, there were no significant differences for the SART test in the change in accuracy of correct responses (T1: +0.002±0.009; T2: -0.004±0.026; T3: -0.022±0.04), reaction time (T1: -21.3±29.6 ms; T2: 5.9±70ms; T3: -9.9±32.6 ms), errors of commission (T1: 0.02±0.07; T2: -0.06±0.13; T3: -0.08±0.13); nor errors of omission (T1: 0.001±0.007; T2: 0.001±0.018; T3: -0.011±0.02, p>0.05). Conclusions: Cognitive performance measured by the SART was not significantly affected by a prolonged cognitively demanding task in thermoneutral conditions, nor when combined with heat stress, despite increased thermal and cardiovascular strain and greater perceptions of heat and discomfort. Moreover, cognitive performance is preserved despite greater reductions in affect when performing a prolonged cognitively demanding task when combined with heat stress. These findings highlight the resilience of cognitive function under heat stress but underscore the psychological and physiological burden of such conditions, which could impact real-world performance and wellbeing in heat-stressed environments. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.