Regulation of energy expenditure during prolonged athletic competition

Background: Athletic competitions, such as the Tour de France, demand both momentary bursts of very high power output and the ability to provide high levels of energy expenditure for several weeks. As such, they provide a model of the ability for sustained muscular activity, which is important in terms of how humans are understood, not only as athletes, but also within an evolutionary context. Methods: Laboratory correlated HR responses were made of elite professional cyclists (N = 7) during successive competitions in one of the three grand tours in cycling in successive years, with the intent of evaluating the magnitude and pattern of energy expenditure. HR recordings were normalized into a training impulse (TRIMP) score, summating the intensity and duration of each race, and tracked over the duration of successive tours. Results: Although the day-by-day pattern of HR responses in exercise intensity zones associated with exercise intensities below the first ventilatory threshold, between the first and second ventilatory thresholds, and above the second ventilatory threshold varied in response to the course and competitive situation, the net accumulation of both time in each of the HR zones and TRIMP was remarkably constant from one tour to the next, both within the group at large as well as within individual athletes. The magnitude of accumulation of TRIMP was similar to that of previous reports on elite tour cyclists. Conclusions: We interpret these results as evidence that humans adopt a pacing strategy designed to optimally distribute energy reserves over the duration of each tour.