Fig. 1.

Schematic of the reaction-diffusion mathematical model showing a one-dimensional spatial domain, where the position in the cell (x) ranges from x = 0 (sarcolemma) to x = L (fiber center), where L is segment length. O₂ is supplied at a fixed concentration (7.85 μM) and transported through a membrane (gray area) with a fixed resistance (1/k_mt, where k_mt is the mass transfer coefficient of O₂ transport from the hemolymph through the cell membrane). O₂ supplies a bulk population of mitochondria uniformly distributed throughout the region from x = 0 to x = L and a boundary population of mitochondria clustered at the fiber's edge (x = 0). The ATPase reaction (e.g., myosin) is distributed uniformly through the spatial domain from x = 0 to x = L. C⁰, O₂ concentration; k₁ and k₂, rate constants; k_2w, rate constant for ATP production at the fiber boundary.