This month’s issue of MSSE features an interesting article by Van Wijck, Wijnands, and colleagues reporting that L-citrulline intake may protect against intestinal injury during strenuous exercise in athletes. L-citrulline is readily converted to L-arginine, which is a precursor of nitric oxide (NO), a potent vasodilator. L-citrulline supplementation reduced exercise-induced splanchnic hypoperfusion and improved microcirculation. Previously, the same group showed that, compared with L-arginine, L-citrulline is a more suitable substrate to enhance intestinal perfusion and microcirculation in endotoxemic mice. With the current study, they translated these findings to humans, showing that intestinal compromise as a consequence of blood redistribution from the splanchnic organs to the working muscles could be prevented by citrulline supplementation. In association with this article, we are making freely available a previous publication by the same group [Aggravation of Exercise-Induced Intestinal Injury by Ibuprofen in Athletes. Med Sci Sports Exerc. 2012;44(12): 2257-2262].
Also featured in this month’s issue is a report of a longitudinal case study of changes in maximal systemic oxygen transport capacity of an Olympic athlete over a 20-year period following his final elite competition. Previous studies inform us that maximal heart rate declines on the order of 0.7 beats per minute per year. The logical consequence would be reductions in cardiac output and maximal oxygen uptake. Usually, the average male can expect a decline of about 1% per year in maximal oxygen uptake. Thus, it seems contradictory that athletes continue to compete in endurance events at the highest international level at least until the age of approximately 40 years. This month, Nybo et al. report on 20 years of annual physiological data of a medal winner at five consecutive Olympic Games. During this period the athlete experienced the expected reduction of maximal heart rate, but maintained maximal oxygen uptake and aerobic exercise ability. Therefore, a reduction of maximal heart rate is not inevitably associated with reduced maximal oxygen uptake or performance deterioration if vigorous physical training is continued. As a supplement to this report, we are making freely available a well-cited article by Saltin and Strange [Maximal Oxygen Uptake: "Old" and "New" Arguments for a Cardiovascular Limitation. Med Sci Sports Exerc. 1992;24(1):30-37].
Also spotlighted this month is a report by Bidwell et al. that nicely illustrates the College’s “Exercise is Medicine” theme. These authors conclude that physical activity tends to ward off the negative effects of fructose in the diet. In young, healthy individuals averaging only about 4,200 steps per day, consumption of an additional 75 g of fructose per day for two weeks caused an increase in postprandial lipidemia and signs of potential low-grade inflammation. However, subjects who were averaging 13,000 steps per day did not experience these adverse changes in response to the added dietary fructose.
L. Bruce Gladden