During a 3-minute submaximal run, which energy systems contribute and how does the fuel mixture shift as duration changes?

During a 3-minute submaximal run, which energy systems contribute and how does the fuel mixture shift as duration changes?

• A. Primarily oxidative energy with minimal anaerobic contribution; as duration increases, fat oxidation rises while carbohydrate usage remains minimal.
• B. Predominantly oxidative energy with some anaerobic glycolysis; as duration increases, reliance on fat oxidation rises while carbohydrate utilization remains high.
• C. Primarily phosphagen energy with decreasing fat oxidation over time.
• D. Only oxidative energy with carbohydrate utilization dropping to zero.

Answer: (B)

During a submaximal run of about three minutes, energy comes mainly from oxidative phosphorylation in the mitochondria. The phosphagen system provides ATP only at the very start, so its role is brief, and there is some contribution from anaerobic glycolysis as glycolysis ramps up to help meet energy needs in the initial phase. As the duration extends, the body shifts toward greater fat oxidation to spare carbohydrate stores. However, carbohydrate utilization does not disappear; it remains substantial because the pace is still relatively high and glycolytic flux continues to supply pyruvate for the mitochondria. In short, energy is predominantly oxidative with some anaerobic glycolysis, and over time fat use increases while carbohydrate use stays meaningfully high.

During a submaximal run of about three minutes, energy comes mainly from oxidative phosphorylation in the mitochondria. The phosphagen system provides ATP only at the very start, so its role is brief, and there is some contribution from anaerobic glycolysis as glycolysis ramps up to help meet energy needs in the initial phase.

As the duration extends, the body shifts toward greater fat oxidation to spare carbohydrate stores. However, carbohydrate utilization does not disappear; it remains substantial because the pace is still relatively high and glycolytic flux continues to supply pyruvate for the mitochondria. In short, energy is predominantly oxidative with some anaerobic glycolysis, and over time fat use increases while carbohydrate use stays meaningfully high.