Just three years ago EPOC was thought to have two components, fast and slow. Fast component represented the oxygen debt required to rebuild ATP and PCr used during ex (exercise). Without sufficient O2, phosphate bonds are broken to supply energy. During recovery, bonds need to be reformed via oxidative process to repay the debt. The slow component was thought to be the removal of lactate from the tissue either by conversion to glycogen or oxidation to CO2 and H2O, therefore providing energy to restore glycogen. Based on this theory people thought that by examining post oxygen consumption, they could guess the amount of anaerobic activity that had occurred. Studies were way off.
But a study done a Queens U and AZ State, about two years ago found that infact that was too simplistic! During the initial phase of ex O2 is borrowed from oxygen store, myglobin and hemoglobin, therefore it must be replenished during recovery. Respiration remains temporarily elevated following exercise partly to clear CO2, that is in the tissue from metabolic waste. Body temp is also elevated that keeps metabolic and respiration rates high, therefore needing more O2. Elevated levels norepinephrine and epinephrine are elevated during ex and also have similar effects.