In the context of oxygen deficit, what best describes the oxygen demand relative to supply at the start of exercise?

• A. Oxygen supply exceeds demand
• B. Oxygen demand is greater than supply
• C. Oxygen demand and supply are equal
• D. Oxygen supply is irrelevant

Answer: (B)

Oxygen deficit occurs at the start of exercise because the muscles immediately need more ATP, but the body's ability to deliver oxygen to those muscles lags behind. The respiratory and circulatory systems take a moment to ramp up oxygen uptake and delivery, so the amount of oxygen being used (supply) is still less than what the muscles require (demand) to support the sudden increase in energy production. To cover this immediate shortfall, the body relies on anaerobic processes to generate energy, and as oxygen delivery catches up, the system can reach a steady state where demand and supply balance.