Identifying Predictors of Fat Oxidation in Response to Exercise Prescribed According to Relative and Metabolic Intensities

Authors

Athrva Deshpande, California State University San MarcosFollow
Todd Astorino Ph.D, Cal State San MarcosFollow

Abstract

Capacity for fat oxidation (FOx) is related to endurance performance and metabolic health. Chrzanowksi-Smith et al. (2021) revealed that maximal O₂ consumption (VO₂max), resting FOx, and physical activity level significantly predict maximal fat oxidation. PURPOSE: To identify predictors of the metabolic response to endurance exercise. METHODS: Active, non-obese men and women (N = 36, age and VO₂max = 24 ± 4 yr and 2.8 ± 0.8 L/min) underwent 3 sessions of cycling separated by 3 – 7 days. All bouts were performed at the same time of day within participants. Initially, body fat and fat-free mass (FFM) were measured using sum of 3 skinfolds, and a ramp test was performed to assess VO₂max, maximal heart rate (HR), and ventilatory threshold (VT). Subsequent sessions included 35 min of cycling at 62 %HRmax and workload = 30 % sub-VT, which were preceded by a 12 hr fast and 36-hour abstention from physical activity. Gas-exchange data and HR were recorded for 3 min pre-exercise and during exercise, and the Frayn equation was used to estimate fat and CHO oxidation (FOx and CHOOx in mg/kg FFM/min). Blood glucose and blood lactate concentration (BLa) were recorded from a fingertip. Significant 3-predictor models of FOx were developed using multiple regression. RESULTS: VO₂max, resting respiratory exchange ratio (RER) (0.86 ± 0.06), and post-exercise BLa (1.4 ± 0.7 mM) accounted for 43 % of variance in FOx in the 62 %HRmax bout (4.4 ± 2.1 mg/kg FFM/min), with slightly higher variance accounted for when exercise PO (W) was entered in lieu of BLa (R = 0.66, R² = 0.44, p < 0.001). Adding CHOOx (15.9 ± 5.0 mg/kg FFM/min, r = -0.51, p < 0.001) to the model accounted for 59 % of the variance in FOx. For the VT bout (FOx = 3.8 ± 2.9 mg/kg FFM/min), VO₂max, BLa (2.8 ± 1.6 mM), and RERrest (0.86 ± 0.07) accounted for 40 % of the variance (R = 0.63, p=0.001). Replacing BLa with CHOOx (27.3 ± 8.6 mg/kg FFM/min) elicited the biggest shared variance (R = 0.75, R² = 0.56, p < 0.001). CONCLUSION: VO₂max was positively correlated with FOx, while resting RER, BLa, and CHOOx are strongly, inversely related to FOx in adults. Body composition and BG were unrelated to FOx. The additional 40 % variance in FOx is likely explained by dietary intake, muscle fiber type, and [glycogen] and remains to be elucidated.

Recommended Citation

Deshpande, Athrva and Astorino, Todd Ph.D (2024) "Identifying Predictors of Fat Oxidation in Response to Exercise Prescribed According to Relative and Metabolic Intensities," International Journal of Exercise Science: Conference Proceedings: Vol. 14: Iss. 4, Article 24.
Available at: https://digitalcommons.wku.edu/ijesab/vol14/iss4/24