The critical power test is a well-established procedure that provides estimates of two important parameters characterizing work performance; anaerobic work capacity (AWC) and critical power (CP). The concept proscribes a hyperbolic relationship between power output (P) and time to exhaustion (t), given by (P - CP)t = AWC. Since evidence now exists that the procedure overestimates CP and underestimates AWC, this study was undertaken to investigate the effect of relaxing the requirement that the time asymptote necessarily be at zero. Using data from a previous study, it is shown that in so doing, (1) a time asymptote significantly less than zero is obtained, (2) significantly smaller estimates of CP and larger estimates of AWC are obtained, (3) a third parameter is introduced that theoretically represents maximal instantaneous power, (4) it implies that the maximal power that could be developed at any instant is proportional to the amount of AWC remaining at that instant, which in turn implies that (5) at exhaustion not necessary all of AWC is consumed.

The model described in this article is a generalised three component hydraulic model, proposed to represent net whole body bioenergetic processes during human exercise and recovery. During exercise, fluid flows from the three interconnected vessels in the system represent the breakdown of high energy phosphates (phosphagens), oxygen consumption and lactic acid production. During recovery, replenishment of the fluids represents the repayment of oxygen debt. The model is quantified and solved mathematically, and the solution compared with observed experimental data. Since currently known physiological facts are consistent with four configurations of this model, further experimentation is necessary.

The critical power test for cycle ergometry has been criticised as providing an overestimate of the real value of the critical power. Part of the blame may rest in the practical problem associated with getting reliable measurements of longer endurance times when power settings are not much above the critical power. However, by adjusting the incremental slope of ramp exercises, exhaustion brought about by high power and in a reasonably short time can be ensured, so avoiding this practical problem. This communication presents the theory and methods required to obtain estimates of both anaerobic work capacity and critical power from several ramp tests conducted to exhaustion. The method is illustrated with published laboratory data collected from exercising subjects.

Women exercising at low intensities in 35°C experienced most statistically significant physiological changes after 70RH. As H and Ereq remained constant across trials, heat storage increased with each 15% rise in RH because dry and respiratory heat losses minimally offset decreased E. Higher Tre, Tsk, and resultantly higher sweat rates reflected heat storage increases as E decreased in each trial. Overall, at 35°C Ta, we found women exercising for 90 min at low intensities remained at safe rectal temperatures up to 70% RH.

The properties of a proposed three component hydraulic model of human bioenergetics are examined in respect of the maximum exertable power and the endurance time for given workloads. An equation expressing the decline in maximal effort during an "all-out" exercise is derived, from which a VO2 time equation can be deduced. In addition a workload versus endurance time equation can be obtained, enabling the prediction of time to exhaustion. The resulting equations are illustrated graphically by means of a numerical example. Model predictions, when compared with experimental results, reveal discrepancies which confirm the rejection of the model, as was suggested in an earlier paper.