As usual, I am highlighting three papers in this month's journal. First, it is quite possible that physical inactivity leads to yet unknown, unhealthy phenomena. In this context, Burton and Coyle take a unique physiological approach to identify how many steps per day appears “healthy" based upon the degree of improvement in fat metabolism on the day after running for one hour. They found that walking either approximately 2,500 or 5,000 steps per day on the days prior to the run resulted in equally impaired fat metabolism, a phenomenon they termed “exercise resistance." However, when 8,500 steps per day were taken, fat metabolism was improved. Using these acute changes in postprandial fat metabolism, these authors proposed the practical recommendation that 5,000 steps per day is inadequate while 8,500 steps per day is sufficient for this exercise benefit. These types of observations are key to developing broad guidelines about the interaction of activity and exercise for improving health.
Second, racecar drivers wear fire protective suits, which hinders their ability to effectively cool themselves via sweating. During races with high ambient temperatures, it is common for drivers to experience a 2°C–3°C increase in core body temperature. Clearly, thermal strain can have catastrophic implications for driver safety. Accordingly, the FIA (sanctioning body for motorsports) has instituted regulations to limit the cockpit temperature of racecars during competition. Barthel and Ferguson evaluated the effectiveness of this regulation at limiting thermal stress in drivers. Their results showed that cockpit temperature was a poor predictor of thermal strain on racecar drivers and they recommended that thermal strain of the driver should be monitored rather than cockpit temperature to ensure driver safety.
Finally, Constantini et al. investigated the relationship between the poikilocapnic hypoxic ventilatory response (HVR) at rest and during exercise along with exercise ventilation, and a true performance measure (i.e., cycling time trial) at simulated moderate altitude as experienced by endurance athletes in competition and training. Exercise HVR was greater than, and not correlated with, resting HVR, even after adjusting for exercise-induced increases in CO2 production. While time trial performance in hypoxia was worse in comparison to normoxia, this decline was not related to ventilatory responsiveness to hypoxia, per se. Several other measures of ventilatory “output" explained a large portion (~85%) of the variance in hypoxic performance impairment. Specifically, their findings indicated that a sufficient, but not exaggerated, hyperventilatory response during exercise is likely essential for mitigating hypoxia-induced impairments in endurance cycling performance.
L. Bruce Gladden
School of Kinesiology