## Core Concept
The question tests the understanding of glucose transport into muscle cells (myocytes), specifically focusing on the type of glucose transporter (GLUT) involved in this process. Glucose transporters are proteins that facilitate the transport of glucose across cell membranes. Different types of GLUTs are present in various tissues, and their actions can be insulin-dependent or insulin-independent.

## Why the Correct Answer is Right
The correct answer, **GLUT4**, is primarily found in adipose tissue and striated muscle (skeletal and cardiac muscle). It plays a crucial role in glucose metabolism by facilitating the uptake of glucose into these cells in response to insulin and muscle contraction. During strenuous exercise, such as running, jumping, and weight lifting, muscle cells require more glucose for energy production. GLUT4 translocation to the plasma membrane is stimulated by muscle contraction and insulin, making it essential for glucose uptake in myocytes during and after exercise.

## Why Each Wrong Option is Incorrect
- **Option A: GLUT1** is widely distributed in various tissues and is responsible for basal glucose uptake. It is not the primary glucose transporter responsive to insulin or muscle contraction in myocytes.
- **Option B: GLUT2** is mainly found in the liver, pancreas, and kidneys, and is involved in glucose sensing and glucose-stimulated insulin secretion. It is not primarily associated with glucose transport into myocytes.
- **Option C: GLUT3** has a high affinity for glucose and is predominantly expressed in neurons, where it ensures a constant supply of glucose for neural function. It is not the key glucose transporter in myocytes.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **GLUT4** is the glucose transporter that is crucial for glucose uptake in skeletal muscle and adipose tissue, and its action is enhanced by both insulin and physical exercise. This is particularly relevant in the context of diabetes management and exercise physiology.

## Correct Answer Line
**Correct Answer: D. GLUT4**.