FAT OXIDATION IS POSITIVELY ASSOCIATED WITH RUNNING PERFORMANCE AFTER STRENUOUS CYCLING IN YOUNG TRIATHLETES

Endurance performance can be predicted by maximal oxygen uptake (VO2peak), sustainable percentage of VO2peak, and energy cost of movement (C) (1). However, during prolonged exercise, the ability to maintain these physiological attributes, i.e., durability, has recently been shown to characterize elite performance, e.g., in cycling (2). Mainly, two metabolic mechanisms are discussed to adversely affect durability: an increase in C, e.g., due to reduced neuromuscular efficiency, and/or increased reliance on fat oxidation (FO) due to gradual glycogen depletion during prolonged exercise. Since the prediction of prefatigued cycling performance has recently been improved by considering FO (3) and in triathlon, running always occurs after cycling, this study investigated C and substrate metabolism in triathletes before and after strenuous cycling to determine their relevance to prefatigued running performance.
Fifteen young squad triathletes (16 ± 1 yrs; 60.8 ± 5.5 mL∙min-1∙kg-1) completed a combined cycling and running incremental protocol. After three 5-min running stages on a treadmill (2.8 + 0.4 m∙s-1, 30 s rest), athletes performed a 15-s sprint test, followed by a 20-min recovery phase, and a 3-min incremental test to exhaustion (~1.5 W∙kg-1 + 20 W) on a cycling ergometer. Following an 8-min rest, another 5-min incremental test to exhaustion (2.8 + 0.4 m∙s-1, 30 s rest) was performed on the treadmill. C, carbohydrate oxidation (CHO), and FO were estimated from spirometric data via indirect calorimetry and compared in the first three running stages under fresh (before) and prefatigued (after cycling) conditions using rmANOVA. Associations between VO2peak, C, and CHO/FO and time to exhaustion (tlim) in the exhaustive incremental running test, were examined by correlation and stepwise regression analysis.
In contrast to unaltered C (4.59 ± 0.34 and 4.53 ± 0.36 J∙ kg-1∙m-1, p = 0.12), mean CHO (2.82 ± 0.45 and 2.07 ± 0.37 g∙min-1, p < 0.001) decreased, while FO (0.14 ± 0.13 and 0.41 ± 0.18 g∙min-1, p < 0.001) increased from fresh to prefatigued running. Besides VO2peak (r = 0.59, p = 0.02), tlim (1610 ± 176 s) correlated with the change in FO (ΔFO) from fresh to prefatigued running (r = 0.49, p = 0.06). Regression analysis identified VO2peak, C, and ΔFO as the most informative model for tlim (adj. R2 = 0.59, p = 0.01).
In young triathletes, CHO significantly decreased and FO increased during running after strenuous cycling compared to before, while C remained constant. Due to the correlation between ΔFO and tlim and higher accuracy when ΔFO was added to the model for tlim, substrate metabolism should be considered for predicting prefatigued running performance in triathlon. In addition, the positive association between ΔFO and tlim suggests that high FO rates may be beneficial for performance and should thus be improved, e.g., by training with low glycogen availability.
1 Joyner, 1991, JAP
2 Mateo-March et al., 2022, IJSPP
3 Maunder et al., 2022, EJAP