The Dietary Influence On Substrate Utilization During A Submaximal Oxygen Consumption Test In Male Combat Sport Athletes And Runners
Authors:   , Stanzione Joseph R. , Volpe Stella L. 
Published: September 2022

Introduction: Crossover point is characterized as the point during exercise when one transitions energy substrates from fat to carbohydrate predominance. Crossover point is applicable to most exercise endeavors and varies based on exercise intensity. However, less is known about crossover point and its specificity towards sports type. Understanding the relationship between crossover point and sport type would be beneficial in understanding the metabolic response to exercise across exercise modalities. In addition, the current state of the research has primarily focused on endurance sports with respect to crossover point; thus, there is a paucity of data on non-endurance athletes (e.g., Combat Sport Athletes). Athletes participating in high intensity sports are an ideal population to study, because most data on substrate use are focused on endurance-related activities. Furthermore, crossover point is intensity driven; but it has been well documented that the constituents of the diet can directly play a role as well. Most studies in this area have focused on a few days of dietary intervention or analyses of an athlete's usual intake. There is information lacking on the immediate influence of a pre-exercise meal on exercise metabolism or the crossover point. Therefore, the purpose of this study were as follows: 1) to analyze differences between Runners, Triathletes, Rowers and CrossFit Athletes, 2) to analyze differences in time to crossover point between a group of high intensity sport athletes (Combat Sport Athletes) and a group of low- to moderate- intensity sport athletes (Runners); and, 3) to examine if two acute dietary interventions and a fasted intervention could alter baseline time to crossover point in a group of healthy athletes. Healthy athletes were defined as those without any metabolic disorders and who could participate in maximal and submaximal exercise. Methods: Participants were recruited from the surrounding Philadelphia area to participate in a four-session crossover study design consisting of a maximal oxygen consumption (VO2max) test and three submaximal tests, each separated by at least one week. The submaximal tests were preceded by either a bolus feeding of carbohydrate, fat or no meal (in a randomized fashion), 30 minutes prior to exercise. Participants were measured via indirect calorimetry during all exercise tests, and crossover point was determined using respiratory exchange ratio (RER), defined as reaching an RER >0.85 with no return below 0.85 for the remainder of the test. Each participant was also measured for anthropometrics, body composition and dietary intake at each session. A one-way ANOVA was applied to determine differences between Runners, Triathletes, Rowers and CrossFit Athletes. A 2x2 factorial ANOVA was conducted to determine if differences existed in heart rate and percent (%) VO2max at crossover point between Combat Sport Athletes and Runners during a VO2max and submaximal test. A Kruskal-Wallis test was applied to determine if differences existed in time to crossover point between Combat Sport Athletes and Runners during a VO2max and submaximal test. A Kruskal-Wallis test was applied to identify differences between sport groups. A Friedman's test was applied to denote the directional effects of two acute dietary interventions and a fasted intervention on time to RER. All statistical procedures were performed with the Statistical Package for the Social Sciences (SPSS) version 24.0, with alpha levels set a priori to p<0.05. Results: We found significant differences between Runners, Triathletes, Rowers and CrossFit Athletes for time to crossover point (p = 0.007) and %VO2max at crossover point (p = 0.018). Significant differences were observed in time to crossover between Combat Sport Athletes and Runners during exercise (p = 0.005). No differences were observed for heart rate and %VO2max. Significant differences were observed between Combat Sport Athletes and Runners during their fasted condition test (p = 0.012). In addition, all athletes exhibited a significantly earlier time to crossover after an acute carbohydrate intervention (p = 0.001). There were no significant differences after an acute fat intervention. Conclusions: This is the first study to identify significant differences in crossover point between specific sport types. Further, this is the first study to analyze Combat Sport Athletes and crossover point. It appears that Combat Sport Athletes have an earlier use of carbohydrate compared to runners, who have a higher affinity for fat oxidation. In addition, all athletes exhibited an earlier use of carbohydrate, compared to fasting, by consuming carbohydrate prior to exercise. Eating fat prior to exercise does not appear to alter crossover point compared to a fasted condition, based on our methodology. More studies are warranted that consider alterations in crossover point and how it can influence sports performance outcomes.