Fourteen days of unilateral knee immobilization in healthy young men is associated with a 9.6% reduction in vastus group muscle cross-sectional area, a 3.3% decrease in leg lean mass, and a 15.6% decline in unilateral leg press strength.

When a leg is immobilized, the muscles stop contracting regularly, so they use less energy. This causes the energy-producing parts of muscle cells to shrink and become less efficient, leading to a buildup of harmful byproducts. The cell responds by activating cleanup systems that break down its own proteins, especially those needed for structure and energy production. As a result, muscle fibers shrink, mass decreases, and the muscle loses its ability to generate force.