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

Abstract

This study investigated the effects of prolonged intermittent cycling exercise on peak power output (PPO) and 6-min time-trial (6min-TT) performance in elite and professional road cyclists. Moreover, the study aimed to determine whether changes inperformance in the fatigued state could be predicted from substrate utilization during exercise and laboratory measures obtained in a fresh state. Twelve cyclists (age: 23years [21;25]; body mass: 71.5kg [66.7;76.8]; height: 181cm [178;185]; O2peak: 73.6ml 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 6min-TT (MPO6min) in a fresh condition. On a separate day, the cyclists completed a 4-h intermittent cycling protocol with a high CHO intake (100gh-1). Substrate utilization and PPO was measured hourly during the protocol, which was followed by another 6min-TT. MPO6min 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 6min-TT was unchanged. Correlation analyses showed no strong associations between reductions in MPO6min 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 MPO6min. PPO and MPO6min were reduced following prolonged intermittent cycling, but the magnitude of these reductions could not be predicted from laboratory measures obtained in the fresh condition.