Individual differences in biophysiological toughness: sustaining working memory during physical exhaustion.

Recent evidence suggests that increased dehydroepiandrosterone sulfate (DHEAS), in combination with decreased cortisol levels have been correlated with enhanced performance outcomes in stressful military environments. This study was implemented to replicate these findings in a group of active duty Air Force members to provide information on the usefulness of these biomarkers indices in the training and operational environment. Seventeen active duty males participated in the 4 sessions of this study. Sessions 1 and 2 were training days for the cognitive testing. Session 3 was a baseline measure of physical fitness, utilizing the VO2 Maximal Treadmill test. Session 4 was centered around a modified-Astrand treadmill protocol designed to induce physical exhaustion. Blood draws for biomarker analysis, cognitive testing (NovaScan), psychomotor vigilance, and physiological measures were collected before, during, and following the treadmill protocol. Results showed that prolonged increases in cortisol negatively correlate with working memory performance. DHEAS release from baseline to poststress was negatively related to the changes in cortisol for 20 minutes following stress. These results indicate that the ratio of DHEAS to cortisol buffers, the effect of cortisol increases that are related to poor working memory performance because of physical exhaustion.