9-Panel plot interpretation

The basic requirement to sustain muscular exercise is an increase in cellular respiration for regeneration of the adenosine triphosphate (ATP) to fuel the muscular contractions. To support the increase in cellular respiration. O2 and CO2 transport between the cells and the environment must match the rate of cellular respiration (except for transient lags allowed by the capacitances in energy  stores and the transport system).  The increase in O2 and CO2 transport are functions of the peripheral circulation, heart, pulmonary circulation, blood, lungs and respiratory muscles. Any defect in this interactive system could result in failure of the exercising muscles to take up and use the O2 needed for anaerobic regeneration of ATP.