During cast immobilization for a fracture, which physiological change is most expected in the immobilized muscle?

• A. Increased capillarity
• B. Decreased capillarity
• C. Increased metabolic rate
• D. Increased blood flow

Answer: (B)

During cast immobilization for a fracture, the immobilized muscle undergoes several physiological changes due to a lack of movement and use. One of the most significant changes is the decrease in capillarity, which refers to the number of capillaries in the muscle tissue that supply oxygen and nutrients.

When a muscle is immobilized, its activity level decreases substantially. This inactivity leads to reduced metabolic demand from the muscle cells, leading to a decrease in blood flow and, consequently, a reduction in the synthesis and maintenance of capillaries. Fewer capillaries can result in insufficient oxygen delivery and nutrient supply to the muscle, which can contribute to muscle atrophy and weakness.

Moreover, the reduced use of the immobilized muscle causes physiological adaptations that favor maintenance of energy balance, but since the metabolic activity is decreased, the stimulus for angiogenesis (the formation of new capillaries) is also diminished. Therefore, the overall effect of immobilization on the muscle is a reduction in capillary density, leading to decreased capillarity as a critical physiological change.