Estimated Cardiorespiratory Response

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Abstract
Cardiorespiratory responses during marathon running (42.2 km) were estimated on nine nationally ranked marathon athletes. Oxygen consumption ([vdot]o2), ventilation ([vdot]E), and heart rate (HR) were predicted from competitive data (average speed) using individual regression equations derived from steady-state values measured in the laboratory. From these predictions, ventilation equivalent ([vdot]E/[vdot]o2) and oxygen pulse ([vdot]o2/HR) were calculated. Stroke volume (q), cardiac output ([Qdot]), and the arteriovenous oxygen difference (a-⫨O2 diff) were estimated as follows: q = q max = Vo2 max/[Hgb] × O2 capacity of Hgb × (SaO2 – S⫨O2) max × HR max; [Qdot] = q × HR; and a-⫨O2 diff = [vdot]o2/[Qdot]. The [vdot]o2 max, HR max, and [Hgb] were measured in the laboratory; (SaO2 - S⫨O2) max was as- sumed to be O.7. These steady-state estimates were evaluated with respect to the effects of race duration and environmental factors. It was concluded that q, [Qdot], and particularly HR are heavily stressed during marathon competition and. In fact, are maintained very nearly at maximal levels (92% to 96% max) throughout the duration of the race. The other variables are taxed to a much lesser extent (69% to 86% max).