<prompt> During exercise, increase in O2 delivery to muscles is because of all exceptOxygen dissociation curve shifts to leftIncreased stroke volumeIncreased extraction of oxygen from the bloodIncreased blood flow to muscles  <response>: Hb-O2 dissociation curve shift to left indicates more affinity of Hb to O2 and thus less delivery of O2 to tissues. Exercise causes increased 2,3 DPG.Shift to left seen in- Increased pH- Decreased 2,3 DPG, temperature, PCO2- HbF FetalShift to right seen in- Decreased pH- Increased 2,3DPG, temperature, PCO2- HbS Sickle cell 