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.

Sex differences in whole body gait kinematics at preferred speeds.

Studies on human perception have identified pelvis and torso motion as key discriminators between male and female gaits. However, while most observers would advocate that men and women walk differently, consistent findings and explanations of sex differences in gait kinematics across modern empirical studies are rare. In the present study we evaluated sex differences in whole body gait kinematics from a large sample of subjects (55 men, 36 women) walking at self selected speeds. We analyzed the data through comparisons of discrete metrics and whole curve analyses. Results showed that in the frontal plane, women walked with greater pelvic obliquity than men, but exhibited a more stable torso and head. Women had greater transverse plane pelvis and torso rotation as well as greater arm swing. Additional sex differences were noted at the hip and ankle. These kinematic results are in line with anectdotal observations and qualitative studies. In order to understand these observations and substantiate some of the explanations previously set forth in the biomechanics literature, we also explored possible reasons for dynamic sex effects, and suggested applications that may benefit from their consideration.