Hemoglobin’s affinity for oxygen
According to the Bohr effect, decreasing the pH in the blood decreases hemoglobin’s affinity for oxygen. During heavy exercise, when the muscles produce a lot of lactic acid, pH decreases which decreases haemoglobin’s affinity for oxygen. This facilitates the unloading of oxygen to tissues in need. Compared to maternal haemoglobin, foetal haemoglobin has more affinity for oxygen.