Which statement best describes why muscles need more fuel during exercise?

Which statement best describes why muscles need more fuel during exercise?

• A. Increased muscle temperature
• B. Muscles require more fuel to function due to increased demand for oxygen and glycogen; more carbon dioxide produced
• C. Lactic acid buildup only occurs after activity
• D. Muscles become cooler instantly after stopping

Answer: (B)

When muscles work harder, their energy demand rises. To meet that demand, muscles burn more fuel—glycogen stored in the muscles and liver, plus glucose from the blood—through respiration. This increased metabolism requires more oxygen, and as the fuels are oxidized, more carbon dioxide is produced as a waste product. So a statement that links the greater energy need to using more oxygen and glycogen and notes the higher production of carbon dioxide best explains why fuel use goes up during exercise. Heat generation is a byproduct of this process, not the trigger for needing more fuel, lactic acid can occur during intense effort and isn’t simply something that only happens after activity, and muscles don’t cool instantly once activity stops.

When muscles work harder, their energy demand rises. To meet that demand, muscles burn more fuel—glycogen stored in the muscles and liver, plus glucose from the blood—through respiration. This increased metabolism requires more oxygen, and as the fuels are oxidized, more carbon dioxide is produced as a waste product. So a statement that links the greater energy need to using more oxygen and glycogen and notes the higher production of carbon dioxide best explains why fuel use goes up during exercise. Heat generation is a byproduct of this process, not the trigger for needing more fuel, lactic acid can occur during intense effort and isn’t simply something that only happens after activity, and muscles don’t cool instantly once activity stops.