Substrate utilization and durability during prolonged intermittent exercise in elite road cyclists

This study investigated the effects of prolonged intermittent cycling exercise on peak power output (PPO) and 6-min time-trial (6 min-TT) performance in elite and professional road cyclists. Moreover, the study aimed to determine whether changes in performance in the fatigued state could be predicted from substrate utilization during exercise and laboratory measures obtained in a fresh state.

Twelve cyclists (age: 23 years [21;25]; body mass: 71.5 kg [66.7;76.8]; height: 181 cm [178;185]; $$ O₂peak: 73.6 ml kg^-1 min^-1 [71.2;76.0]) completed a graded submaximal cycling test to determine lactate threshold (LT₁), gross efficiency (GE), and maximal fat oxidation (MFO) as well as power output during a maximal 6 min-TT (MPO_6 min) in a fresh condition. On a separate day, the cyclists completed a 4-h intermittent cycling protocol with a high CHO intake (100 g h^-1). Substrate utilization and PPO was measured hourly during the protocol, which was followed by another 6 min-TT.

MPO_6 min and PPO was reduced by 10% [4;15] and 6% [0;6], respectively, after the cycling protocol. These reductions were accompanied by reductions in the anaerobic energy contribution and $$ O₂peak, whereas the average $$ O₂ during the 6 min-TT was unchanged. Correlation analyses showed no strong associations between reductions in MPO_6 min and PPO and laboratory measures (i.e., LT₁, GE, MFO, $$ O₂peak) obtained in the fresh condition. Additionally, fat oxidation rates during the cycling protocol were not related to changes in neither PPO nor MPO_6 min.

PPO and MPO_6 min were reduced following prolonged intermittent cycling, but the magnitude of these reductions could not be predicted from laboratory measures obtained in the fresh condition.