Which energy system is preferentially used when exercise intensity is low and oxygen supply is high?

Which energy system is preferentially used when exercise intensity is low and oxygen supply is high?

• A. Glycolytic
• B. Creatine phosphate system
• C. Aerobic
• D. Lactate shuttle

Answer: (C)

When exercise is easy and oxygen is plentiful, energy is produced mainly through aerobic metabolism. Oxidative phosphorylation in mitochondria uses substrates like carbohydrates and fats to generate ATP efficiently, giving a large energy yield that can sustain activity for longer periods. The creatine phosphate system provides energy only for a very short, rapid burst, so it isn’t the main source here. Anaerobic glycolysis would dominate if oxygen were limited or intensity higher, because it can produce ATP quickly without relying on oxygen, but it’s less efficient and leads to lactate buildup. The lactate shuttle describes how lactate can be used as fuel, but it isn’t the primary energy source at low intensity with high oxygen.

When exercise is easy and oxygen is plentiful, energy is produced mainly through aerobic metabolism. Oxidative phosphorylation in mitochondria uses substrates like carbohydrates and fats to generate ATP efficiently, giving a large energy yield that can sustain activity for longer periods. The creatine phosphate system provides energy only for a very short, rapid burst, so it isn’t the main source here. Anaerobic glycolysis would dominate if oxygen were limited or intensity higher, because it can produce ATP quickly without relying on oxygen, but it’s less efficient and leads to lactate buildup. The lactate shuttle describes how lactate can be used as fuel, but it isn’t the primary energy source at low intensity with high oxygen.