Final answer:
Elevated CO2 partial pressure, higher temperature, and lower pH all contribute to decreased oxygen affinity in hemoglobin, allowing more oxygen to be delivered to working muscles.
Step-by-step explanation:
The conditions at a working muscle that contribute to a change in oxygen affinity of blood include elevated CO2 partial pressure, higher temperature, and lower pH. These factors influence the oxygen-hemoglobin dissociation curve due to the Bohr effect, where increased levels of carbon dioxide (CO2) in the blood react with water to form bicarbonate and hydrogen ions, leading to a decrease in blood pH. This lower pH, along with the increased temperature from muscular exertion, decreases hemoglobin's affinity for oxygen, facilitating oxygen dissociation to supply active tissues with more oxygen.