Modelling human power and endurance.

A generalised three component hydraulic model has been proposed to represent the human bioenergetic processes relating internal energy stores to performance during exercise, and into recovery. Further development of the model allows testable predictions to be made. In particular in this paper I examine certain hypotheses of chemical fuel shortage as a subgroup of the potential causes of fatigue, and their implications for maximal power and for endurance. The assumption that the limitation to sustainable power is direct proportionality to the glycogen store remaining, appears the most feasible. Based on this assumption, equations for the decline in maximum attainable power over time, the endurance at fixed workrates and the endurance at incremental tests (as a function of the increment slope) are obtained. Using published data for fit males, the maximum exertable power declines after about 6 s at 972 W to very low levels after about 2 min. For constant powers selected between 208 and 927 W, endurance declines from ad infinitum to only 6 s. Endurance at VO2max is predicted to be about 9 min. For incremental exercise tests of slope ranging from 30 W/min to 60 W/min, endurance lessens from 14 to 9 min. In these tests the anaerobic threshold is reached in times between 6 and 3 min. Although the power at termination of a test increases with incremental slope, terminal oxygen consumption is effectively constant. Almost all these model predictions are observed to correspond well with published experimental findings. These results suggest that the model can be used to represent an adequate overview of the operation of the human bioenergetic system.