Periodised Carbohydrate Intake Does Not Affect Substrate Oxidation but May Contribute to Endurance Capacity

The aim of this study was to investigate whether periodising carbohydrate intake around specific training sessions will enhance endurance training adaptations. Seventeen healthy recreationally endurance-trained males (n = 5) and females (n = 12) (27.5 ± 5.4 years) participated in a four-week training intervention. Participants were divided into two groups: FASTED (stayed fasted between evening high-intensity interval training session and low-intensity training session in the following morning) and FED (no restriction in food intake). Pre- and post-testing included peak oxygen uptake (VO2peak), anaerobic capacity, and 60 min submaximal running tests. Fasted venous blood samples were drawn for the determination of triglyceride and glucose concentrations. VO2peak increased in both FASTED (4.4 ± 3.0%, p=0.001) and FED (4.6 ± 4.2%, p=0.017), whereas maximal running velocity increased only in the FASTED (3.5 ± 2.7%, p=0.002). Lactate concentrations in the anaerobic test after intervention were greater in FASTED than FED (p=0.025-0.041). Running time in the anaerobic test was improved in FASTED (from 64.1 ± 15.6 to 86.3 ± 23.2 s, p<0.001) but not in FED (from 56.4 ± 15.2 to 66.9 ± 21.3 s, p=0.099). Substrate oxidation did not change after intervention in either of the groups (p=0.052-0.597). Heart rate was lower in the submaximal running test in FASTED (p<0.001) but not in FED (p=0.097). Training with periodised carbohydrate availability does not have any effect on substrate oxidation. However, it seems to enhance the capacity to perform high-intensity exercise.