Train Low, Compete High? Fasting before exercise ?

While high-intensity interval training has long been considered a proven strategy to improve both aerobic and anaerobic endurance, emerging evidence suggests that fasting before activity may be one way to make sure you are getting the most out of your workout. The findings in a number of studies contradict traditional wisdom that training is best completed with normal to high carbohydrate levels. According to a review by Pim Knuiman and colleagues of the research published in Nutrition & Metabolism, engaging in high-intensity workouts while glycogen levels are low may enhance the capacity for muscles to oxidize fat and generate energy. While it is widely known and accepted that carbohydrates are the fuel for a single, prolonged workout or endurance activity, research is beginning to show that withholding carbohydrates in advance of training sessions may not affect performance and help to burn fat more efficiently. And some studies do not rule out the possibility that it may actually improve performance over time. “Indeed, several studies have reported that endurance exercise with low glycogen Train Low, Compete High? Fasting Before Exercise May Be Good availability may be a strategy to augment the response in exercise-induced signaling associated with improved oxidative capacity . . . and potentially enhance exercise performance,” according to the review authored by Pim Knuiman, Maria T. Hopman, and Marco Mensink of Wageningen University in the Netherlands. Here’s what some of those studies have shown: • In one study, 14 well-trained cyclists performed nine high-intensity training sessions and nine aerobic training sessions—some with high-glycogen levels at the time of the workouts and others with depleted glycogen levels. During the study period, time trial performance improved by about 10 percent for both groups, and fat oxidation increased in the low-glycogen group, “which may have been due to the enhanced metabolic adaptations in skeletal muscle,” according to the study’s authors. • In another study, 23 “recreationally active men” in three groups completed a 24-week training regimen of high-intensity running. Two groups started training sessions with glycogen levels depleted by 35 to 40 percent after consuming a low-carb lunch, but one of those groups consumed a glucose supplement immediately before and during exercise. The third group completed training under normal conditions, and all three groups reverted to their habitual diet on nonactivity days. The lowglycogen group that did not receive a supplement showed increases as high as 70 to 76 percent in oxidative activity in their leg and thigh muscles following the training regimen, whereas the other groups showed gains between 17 and 53 percent— although the increased oxidative activity did not translate to better performance. • In a third study, 20 young men took up cycling for six weeks; half of them worked out after missing breakfast, and the other half worked out 90 minutes after eating a carbohydraterich breakfast. Gains in performance were nearly identical in the two groups after the training regimen, Patrick Wade, KT Staff Write Page 18 Kinesiology Today Winter 2017 Volume 10, No. 1 www.americankinesiology.org Continue on Page 21 and the ability to oxidize fat was nearly 21 percent higher in the lowcarb group. But again, the difference did not translate to enhanced performance; the study’s authors suggest that the reason may be that the training itself did not subject the athletes to the intensity of a real-life competition. The authors of the review say there are still some unknowns. For example, the body of research is not clear on how glycogen levels affect fat oxidation or energy levels in highly trained athletes versus novices, and in different kinds of exercise. Training parameters like time, intensity, and frequency varied widely from study to study. Notably, the majority of the research shows no difference in performance gains between low- or high-glycogen training regimens. In some, performance gains were less pronounced in the low-glycogen groups compared to those training under normal conditions. While further research certainly is needed, the authors say there may be something there. “[T]he low glycogen approach seems promising with regard to the adaptive response following exercise,” the authors write. “Therefore, low glycogen training may be useful as part of a well-thought out program.