Crossover Point Differences in Combat Sport Athletes and Runners during Exercise Testing

ABSTRACT Introduction During exercise, substrate utilization is characterized by “crossover point,” a term representing the predominant transition from fat to carbohydrate. Exercise intensity highly influences crossover point, but there is a paucity of research on sport-specific differences. The purpose of this study was to examine differences in time to crossover, heart rate (HR), and percent maximal oxygen consumption (%V˙O 2max ) at crossover point between combat athletes and runners during maximal and submaximal tests. Differences in blood lactate, ketone, and glucose responses between sports were also analyzed. Methods Eight male combat athletes and 18 runners were measured for respiratory exchange ratio (RER) during V˙O 2max and submaximal treadmill tests. A Kruskal–Wallis test was applied to determine differences between sport types for time to crossover during both tests. A two-way mixed factorial analysis of variance (ANOVA) was applied, including sport type and exercise test as the between- and within-group factors, respectively. The dependent variables included HR and %V˙O 2max at crossover. For capillary sampling, a two-way mixed ANOVA was applied with blood lactate, ketone, and glucose concentrations as dependent variables. Alpha levels were determined a priori at P < 0.05. Results A significant difference was observed between combat athletes and runners (average age: 32.5 ± 12 yr) in time to crossover point during the submaximal test ( P = 0.009). Combat athletes reached crossover point earlier (10:03 ± 3:21 min) than runners (17:30 ± 6:21 min). No differences were observed for any other measurements ( P > 0.05). Conclusion Differences observed between combat athletes and runners suggest sport-specific metabolic adaptations. Runners had a longer time to crossover than combat athletes, indicating longer fat utilization. Future prospective studies should include a variety of exercise intensities to further elucidate differences in the transition of fuel use between sport types.