Which statement is true about oxygen delivery during aerobic exercise?

• A. Oxygen delivery is unnecessary for any exercise.
• B. All exercise occurs without oxygen.
• C. During warm-up oxygen is not needed.
• D. During aerobic exercise the heart can supply the oxygen that muscles need.

Answer: (D)

During aerobic exercise the muscles rely on oxygen to produce energy through aerobic metabolism. The heart plays a key role by increasing cardiac output—pumping more blood and at a faster rate—so more oxygen-rich blood is delivered to working muscles. This enhanced oxygen delivery supports sustained, moderate-intensity activity, making the statement that the heart can supply the oxygen muscles need true. The other ideas clash with how energy is produced during exercise: oxygen is not unnecessary for any exercise, as aerobic metabolism requires it; not all exercise occurs without oxygen, and even warm-up movements demand oxygen to meet gradual increases in energy demand.