Integrating Cognitive and Mood Assessments into the Heat Tolerance Test for Male Soldiers After Exertional Heat Injury: A Prospective Observational Study

Background: The Heat Tolerance Test (HTT) is widely used to evaluate physiological recovery following exertional heat injury (EHI). However, the current protocol does not assess neurocognitive or affective recovery, which may remain impaired despite normalization of core temperature and heart rate. This study examined whether brief, field-deployable assessments of sustained attention and mood state could discriminate between heat-intolerant (HI) and heat-tolerant (HT) individuals during the HTT. Results: Seventy male combat soldiers (20.3 ± 1.2 years) with a history of EHI completed the HTT; 14 (20%) were classified as HI. Compared to HT counterparts, HI individuals exhibited significantly slower mean reaction times (MeanRT) on the Psychomotor Vigilance Test at 60 min (t (13) = − 8.13, p < 0.001, d = − 2.17) and 120 min (t (13) = − 12.31, p < 0.001, d = − 3.29). They also demonstrated fewer valid responses, more premature responses, and more timeouts (p < 0.01). Total Mood Disturbance (TMD) increased significantly in the HI group from baseline (6.7 ± 12.7) to 120 min (63.4 ± 6.5), with significant between-group differences (p < 0.001). ROC analyses showed that MeanRT (AUC = 0.807, 95% CI: 0.72–0.90) and TMD (AUC = 0.856, 95% CI: 0.79–0.93) effectively discriminated HI status. Additionally, baseline TMD significantly predicted MeanRT at 120 min (p < 0.001), suggesting that mood disturbance is associated with cognitive decline under thermal strain. Conclusions: HI individuals exhibited substantial impairments in vigilance and mood during the HTT, despite achieving physiological recovery. Incorporating brief cognitive and affective metrics into post-EHI assessments enhances the diagnostic sensitivity of the HTT and may inform return-to-duty decisions in both military and civilian contexts where thermal strain compromises operational performance.