Sixty days of bed rest causes a significant reduction in maximal voluntary isometric knee extension and flexion torque, with women experiencing a greater decline than men in both knee extension (−39.7% vs. −25.1%) and knee flexion (−32.9% vs. −10.2%), indicating sex-specific vulnerability to disuse-induced muscle weakness.

When muscles are not used for a long time, the body produces more myostatin, which stops muscle fibers from growing and causes them to shrink. At the same time, harmful molecules build up in the muscle, damaging its structure. Women experience a stronger increase in myostatin and a weaker activation of protective antioxidant systems, so their muscle fibers shrink more and their nerve-muscle connections break down faster, making them lose more strength than men.