PURPOSE: This study investigated the combined effects of thermal strain, progressive dehydration, and prolonged exercise on cognitive performance, in a sample of naturally menstruating females. 

METHODS: Twelve recreationally trained, naturally cycling females completed two (dehydrated, hydrated) experimental sessions. Experimental days were separated by at least one menstrual cycle, and were conducted in the mid-luteal phase of the cycle. In both sessions, participants rode on a cycle ergometer in an environmental chamber set to 40 °C, 20% relative humidity, for three 45-minute work bouts. Work intensity over each bout was prescribed from a previously determined maximal power output, and replicated for both sessions. Work rates were set to 45%, 35%, and 25%, of maximal power output (watts) for the three work bouts, respectively. At the end of each work bout, cognitive performance was assessed using a 10-minute computerised cognitive battery, consisting of a Parametric Go/No-Go (PGNG), Corsi Block Tapping (CBT), and Stroop task. Venous blood samples and clothed body mass values were also collected at the end of each bout. Participants were not permitted to exit the chamber during the session. In the dehydrated condition, no fluid was consumed; in the hydrated condition, compensation of body mass loss at the end of each work bout dictated the fluid replacement for the proceeding work bout.

RESULTS: Core temperature responses were significantly higher (p<.001) in the dehydrated condition, across all three work bouts (mean difference = 0.12 °C, 0.39 °C, 0.65 °C). Percentage of body mass loss was significantly higher (p<.001) in the dehydrated (M= -3.51, SD=0.94%), than the hydrated (M= -0.70, SD=0.62%) condition, and serum osmolality was significantly lower (p<.001)  in the hydrated (M=283, SD=004 mOsm·kg⁻¹), than the dehydrated (M=303, SD=007 mOsm·kg⁻¹) condition. Reaction time was detrimentally affected by time and dehydration (p<.001) in the PGNG, whilst accuracy remained unaffected. CBT performance was consistently higher across the hydrated condition (p=.042). Accuracy and interference effects in the Stroop task were non-significant for the main effects of both time and condition. 

CONCLUSION: While core temperature, body mass and serum osmolality was detrimentally influenced by the dehydrated trial, results of the cognitive performance tasks were inconsistent. Working memory and simple reaction time scores showed reduced performance across the dehydrated condition. However, the Stroop task did not demonstrate any significant performance changes as a result of time, or condition effects. Where the influence of environmental and physiological stressors does not appear to act uniformly on assessments of cognitive performance in naturally cycling females, future research should consider the applicability of specific tasks to occupational and athletic demands. 

DISCLOSURE: The authors have nothing to disclose.