Fifteen minutes into a 10 -kilometer run, what is the major...

Fifteen minutes into a 10 -kilometer run, what is the major energy source of the leg muscles?
a. Preformed ATP
b. Glycolysis
c. Oxidative metabolism
d. Pyruvate and lactate
e. High-protein drink consumed right before the race

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Key Concepts

Immediate Energy System

The immediate energy system relies on preformed ATP stored in muscles and the rapid resynthesis of ATP from creatine phosphate. This system provides a quick burst of energy for very short-duration, high-intensity activities, although its contribution is limited in longer-duration exercise.

Energy Systems in Exercise

The concept of energy systems in exercise refers to the coordinated activation of different metabolic pathways—immediate, anaerobic glycolysis, and aerobic metabolism—to meet the energy demands of physical activities. The dominant energy system shifts based on the duration and intensity of the exercise.

Aerobic Metabolism

Aerobic metabolism, also known as oxidative metabolism, is the process by which cells use oxygen to convert carbohydrates, fats, and proteins into adenosine triphosphate (ATP) for prolonged, moderate-intensity exercise. It is highly efficient and becomes the predominant energy source during activities that last more than a few minutes.

Anaerobic Glycolysis

Anaerobic glycolysis is the metabolic pathway that breaks down glucose into pyruvate without the use of oxygen, rapidly producing a small amount of ATP along with lactate as a byproduct. It plays a key role during short bursts of high-intensity effort or when oxygen availability is limited.

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