Modeling O2 transport as an integrated system limiting (V) over doto2MAX

Maximal endurance exercise capacity is determined by a variety of factors, including maximal ability to transport O-2 to the muscle mitochondria and to use this O-2 for ATP generation ((V) over doto(2)MAX). This analysis combines the individually well-known O-2 mass conservation equations for the four critical steps in the O-2 transport pathway (ventilation, alveolar/capillary diffusion, circulation and muscle diffusion) into an analytical, closed form, model showing how (V) over dotO(2)MAX depends on all four steps. It further shows how changes in any one step affect the function of the others. This analytical approach however requires approximating the O(2)Hb dissociation curve as linear. Removing this condition to allow for the real O(2)Hb curve requires numerical analysis best explained graphically. Incorporating maximal mitochondrial metabolic capacity to use O-2 allows prediction of when (V) over dotO(2)MAX is limited by transport or by metabolic capacity. This simple approach recapitulates in vivo behavior and clarifies the determinants of maximal exercise. (C) 2010 Elsevier Ireland Ltd. All rights reserved.