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

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 (V) over dot O-2 (max) similar to 74 ml.kg(-1).min(-1)). In each testing session, subjects performed a ramp test until exhaustion on a cycle ergometer (workload increases of 25 W.min(-1)). The following variables were recorded every 100 W until the tests: oxygen consumption ((V) over dot O-2, in l.min(-1)), respiratory exchange ratio (RER in (V) over dot CO2.(V) over dot O-2(-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.