Several industries experience periods of cold exposure and rewarming throughout the workday but mental performance under these conditions is unknown. A better understanding of cognition during the rewarming phase after cold exposure may help reduce accidents and improve performance. Ten young men (wearing ∼0.1 clo) underwent three consecutive mornings trials where they were exposed to cold air (10°C) and then subsequently rewarmed (25°C air). A computerised test battery was administered during each stage of the protocol to determine working memory, choice reaction time, executive function and maze navigation. Rectal and skin temperature, oxygen consumption and thermal sensation were also measured throughout and showed a typical response. Relative to baseline performance, working memory, choice reaction time and executive function declined during exposure to 10°C, and these impairments persisted 60 min into the recovery period (i.e. once physiological parameters had returned to baseline). Further work is needed to develop countermeasures to this predicament. Practitioner Summary: This study showed that working memory, choice reaction time and executive function declined during exposure to 10°C air, and these impairments persisted 60 min into the rewarming period (i.e. once measurable physiological parameters had returned to normal). Individuals may be at risk for injury after removal from a cold environment.

Muller MD, Ryan EJ, Kim C-H, Bellar DM, Blankfield RP, Glickman EL. Reliability of the measurement of stroke volume using impedance cardiography during acute cold exposure. Aviat Space Environ Med 2010; 81:120–4. Introduction: It is well documented that cardiovascular alterations occur during acute cold exposure (ACE). Interindividual variability is present, due mainly to body size differences, gender, and age. However, no study has evaluated stroke volume in the same individual twice in the same ambient conditions (i.e., test-retest reliability). Impedance cardiography (ICG) has become a popular method to acquire hemodynamic data in both clinical and applied physiology settings. Further, ICG does not interfere with other dependent variables such as oxygen consumption. Therefore, based on the uniqueness of the methodology, we sought to test reliability in this technology at 5°C for 65 min on two separate occasions. Methods: Nine young men underwent two 65-min trials of resting ACE, separated by at least 72 h. Volunteers were clothed in approximately one layer of clothing. Core and skin temperatures, oxygen consumption, and central hemodynamics were measured. Results: As expected, core and skin temperature decreased while oxygen consumption showed a modest increase over time. In both trials, stroke volume significantly increased over time as heart rate decreased. There was similarity within subjects and between trials for all variables, as assessed via bivariate correlations. Conclusion: Cold increased stroke volume and decreased heart rate when subjects were pooled together, but each subject retained his individuality (minimal interindividual differences). Results suggest that impedance cardiography may be a reliable technique to use during acute cold exposure.

Inadequate energy intake induces changes in endogenous glucose production (GP) to preserve muscle mass. Whether addition provision of dietary protein modulates GP response to energy deficit is unclear. The objective was to determine whether exercise-induced energy deficit effects on glucose metabolism are mitigated by increased dietary protein.

Dehydration limits the appropriate delivery of oxygen and substrates to the working muscle. Further, the brain’s ability to function may also be compromised whereby thermal sensation and mood state may be altered. The purpose of the present investigation was to compare the thermoregulatory, perceptual, and negative mood state profile in glucose (GLU) vs. non-glucose beverage (NON-GLU) condition. Ten healthy men volunteered and were counterbalanced either a GLU or NON-GLU containing beverage on separate mornings. In each condition, they were exposed to 37°C, 50% relative humidity (RH) for baseline, exercise, rehydration, and recovery periods. The exercise period elicited the desired level of dehydration (mean of 2.6 ± 0.3% body weight losses). Upon completion of the protracted exercise, participants were administered either a GLU or NON-GLU containing electrolyte based sports drink ad libitum for 30 min, followed by a recovery period of 15 min in 37°C, 50% RH. Rectal (Tre) and mean skin temperatures (Tsk) were continuously monitored. Gagge (TS) and heated thermal sensation (HTS), profile of mood state (POMS) were measure at the end of each period. During recovery after rehydration, Tre was not significantly different between conditions (GLU vs. NON-GLU) (37.4 ± 0.8 vs. 37.0 ± 1.2°C); Tsk was also not affected by rehydration in both conditions (36.0 ± 0.5 vs. 36.0 ± 0.6°C) and, TS and HTS did not differ between conditions (0.9 ± 1.3 vs.1.3 ± 0.7) and (1.0 ± 0.8 vs.0.8 ± 0.3). Total mood disturbance (TMD) score for the POMS was utilized for overall negative mood state and demonstrated a main effect for time (p < 0.05). TMD during recovery was decreased compared to before hydration in both conditions. The non-glucose containing beverage maintained plasma volume and was effective at maintaining body temperature homeostasis in a similar fashion compared to the glucose containing beverage. Furthermore, negative mood state was not different between the two conditions. The non-glucose beverages can serve a valuable role in the exercise environment depending upon the sport, the ambient temperature, the individual, duration of the exercise, the age and training states of the individual.

This study investigated the effect of cold-water hand immersion on selective attention as measured by the Stroop Color Word Test in nomorbaric normoxia and hypoxia. Ten healthy men rested for 60 min, after which they immersed their non-dominant hand into 5 °C water for 15 min. The interference score of the Stroop Color Word Test and thermal sensation were measured at baseline in the final 5 min of resting and in the final 5 min of cold water hand immersion. The interference score was not influenced by hypoxia but was found to be significantly improved compared to resting in both conditions during cold water hand immersion. Selective attention improved during 15 min of cold-water hand immersion, with increased thermal sensations rated as “very cool” of the immersed arm. Cold-water hand immersion may be helpful in improving cognitive function in normoxia and normobaric hypoxia.

A sudden increase in exercise and energy expenditure is associated with an increase in protein turnover and nitrogen excretion. This study examined how a sudden increase in exercise-induced energy expenditure affected whole body protein metabolism and nitrogen balance in people of differing levels of aerobic fitness. We hypothesized that alterations in whole-body protein turnover would be attenuated, and nitrogen balance would be preserved, in individual with higher levels of aerobic fitness.