A. Kalafatis, K. Beisel, E. Donahue, K. Christison, C.L. Dumke, FACSM

University of Montana, Missoula, MT

Research has demonstrated multiple factors contributing to maximal fatty acid oxidation (MFAO). However, less is known about factors that regulate changes in fatty acid oxidation during exercise. PURPOSE: The purpose of this study is better understand how cycling at MFAO for 60 minutes will alter fat oxidation. METHODS: Twelve fasted, uncaffeinated individuals (8 males, 4 females, average VO2max = 44.3± 2.3 mL·kg-1·min-1, average age =23.7±0.8) underwent two laboratory visits. They first underwent a VO2 max test in which heart rate (HR), rating of perceived exhaustion (RPE), absolute fat (FAO) and carbohydrate oxidation (CHOO) were recorded. Hydrostatic weighing was used to determine body fat percentage. The second visit included a 60-minute exercise on a cycle ergometer at the subjects predetermined maximal fatty acid oxidation (MFAO) workload (0.55±0.05 g·min-1; 58.6±1.1 % VO2max; 126.7±9.6 W). HR, RPE, and the respiratory exchange ratio were recorded every fifteen minutes, with water provided at 3 ml·kg-1 at 15, 30, and 45 minutes. Lactate and glucose were measured at 30 and 60 minutes. Data were analyzed using repeated measures ANOVA, and paired samples T-test for pre- and post changes. RESULTS: There was a main effect of time on HR (154.7±3.5 at 15min, vs 168.0±2.9 bpm at 60min; p=0.005), RPE (11.2±0.3 at 15 min vs 13.8±0.4 at 60 min; p=0.001) and FAO (0.46±0.05 at 15 min vs. 0.65±0.06 at 60 min; p<0.001). FAO at the end of 60 mins of exercise was significantly greater than MFAO (p=0.04) from the VO2max test. The change in FAO during exercise did not correlate with subject characteristics. However, MFAO was superior in the tallest (r=0.67, p=0.02), heaviest (r=0.78, p=0.003), and those with the greatest maximum workload (r=0.82, p=0.001). Correlation was found between the tallest and weight loss during the trial (r=0.66, p=0.019). CONCLUSION: These data suggest that during the 60 minute bike ride that FAO exceeds the MFAO during a VO2max test. In addition, the largest subjects with the greatest maximum workload had the highest MFAO and FAO during the one hour trials.

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