Metabolic and neuromuscular adaptations to endurance training in professional cyclists: A longitudinal study

Abstract

The aim of this longitudinal study was to analyze the changes in several metabolic and neuromuscular variables in response to endurance training during three defined periods of a full sports season (rest, precompetition and competition). The study population was formed by thirteen professional cyclists (age±SEM: 24±1 years; mean V̇O2 (max) ~74 ml · kg-1 · min-1). In each testing session, subjects performed a ramp test until exhaustion on a cycle ergometer (work-load increases of 25W · min-1). The following variables were recorded every 100W until the tests: Oxygen consumption (V̇O2 in/min-1), respiratory exchange ratio (RER in V̇CO2·V̇O2-1) and blood lactate, pH and bicarbonate concentration [HCO3-]. Surface electromyography (EMG) recordings were also obtained from the vastus lateralis to determine the variables: Root mean square voltage (rms-EMG) and mean power frequency (MPF). RER and lactate values both showed a decrease (p<0.05) throughout the season at exercise intensities corresponding to submaximal workloads. In contrast, no significant differences were found in mean pH or [HCO3-]. Finally, rms-EMG tended to increase during the season, with significant differences (p<0.05) observed mainly between the competition and rest periods at most workloads. In contrast, precompetition MPF values increased (p<0.05) with respect to resting values at most submaximal workloads but fell (p<0.05) during the competition period. Our findings suggest that endurance conditioning induces the following general adaptations in elite athletes: (1) lower circulating lactate and increased reliance on aerobic metabolism at a given submaximal intensity, and possibly (2) an enhanced recruitment of motor units in active muscles, as suggested by rms-EMG data.