Estimated Cardiorespiratory Response

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).