**Question:** Sprinter gets its immediate energy from -

A. Glycogen
B. Fat
C. Proteins
D. Glucose

**Core Concept:**
The human body has three primary energy sources: Glycolysis, Kreb's cycle, and Oxidative Phosphorylation. These processes occur in the mitochondria to produce ATP (Adenosine Triphosphate), the body's primary energy currency. In high-intensity activities like sprinting, the body relies on Glycolysis and the less efficient Oxidative Phosphorylation for energy production.

**Why the Correct Answer is Right:**
For a sprinter, the immediate energy source is D. Glucose because Glycolysis and Oxidative Phosphorylation are highly efficient when glucose is the substrate. In sprinting, the body breaks down glucose (from glycogen stored in muscles and liver) via Glycolysis, generating pyruvate and NADH. Pyruvate enters the mitochondria, where it undergoes Kreb's cycle and Oxidative Phosphorylation to produce ATP. Glucose is the preferred energy source for high-intensity activities due to its quick availability and efficiency in the mitochondria.

**Why Each Wrong Option is Incorrect:**
A. Glycogen is the primary energy source during prolonged activities like endurance running or walking. However, in sprinting, the energy demand is too high for glycogen reserves, making glucose the more suitable option.
B. Fat is the primary energy source during prolonged activities (e.g., marathons) due to its storage capacity and slow release rate. In sprinting, the energy demand is too high for fat to be an efficient energy source.
C. Proteins are not used for energy production, as they are structural components and the body would waste valuable amino acids to generate energy, leading to muscle breakdown and wasting.

**Clinical Pearl:**
Understanding energy production pathways during high-intensity activities is crucial for medical students and physicians, especially when diagnosing and treating patients with mitochondrial disorders affecting energy production.