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

Area of Science:

• Sports Science
• Exercise Physiology
• Cycling Performance

Background:

• Elite cyclists undergo rigorous training involving prolonged intermittent exercise.
• Assessing performance decrements and their predictors is crucial for optimizing training and competition strategies.

Purpose of the Study:

• To investigate the impact of prolonged intermittent cycling on peak power output (PPO) and 6-minute time-trial (6-min-TT) performance.
• To determine if performance changes in a fatigued state can be predicted by substrate utilization during exercise and laboratory measures in a fresh state.

Main Methods:

• Twelve elite cyclists completed a graded submaximal cycling test to assess lactate threshold (LT1), gross efficiency (GE), maximal fat oxidation (MFO), and 6-min time-trial power output (MPO6min) in a fresh condition.
• Participants then underwent a 4-hour intermittent cycling protocol with high carbohydrate intake, during which substrate utilization and PPO were measured hourly.
• A final 6-min-TT was performed post-protocol to assess performance after fatigue.

Main Results:

• A significant reduction in MPO6min (10%) and PPO (6%) was observed after the prolonged cycling protocol.
• These performance reductions were associated with decreased anaerobic energy contribution and peak oxygen uptake (VO2peak), while average VO2 during the 6-min-TT remained unchanged.
• No significant correlations were found between performance reductions and laboratory measures (LT1, GE, MFO, VO2peak) in the fresh state, nor with fat oxidation rates during the protocol.

Conclusions:

• Prolonged intermittent cycling exercise leads to significant reductions in both peak power output and 6-minute time-trial performance in elite cyclists.
• Laboratory-based physiological and metabolic measures obtained in a fresh state are not reliable predictors of performance decrements following such exercise protocols.