What is the most likely cause of calf muscle atrophy in a 40-year-old man who underwent Achilles tendon surgery?

Calf muscle atrophy following Achilles tendon surgery in this patient is most likely due to increased protein degradation. After any surgical procedure, particularly one involving immobilization, muscle disuse tends to occur. When a muscle is not used regularly, the body responds by reducing muscle mass, primarily through the process of protein catabolism, which breaks down muscle proteins. This catabolism can be exacerbated by inflammatory responses following surgery, which can lead to an increase in the production of protein-degrading enzymes such as ubiquitin-proteasome pathway components and autophagy-related proteins.

The other options are less directly related to the immediate situation following the surgery. Decreased glycogen synthesis typically has a more significant impact on energy availability rather than directly causing muscle atrophy. Mitochondrial damage affects cellular energy production but does not directly initiate atrophy processes. Necrosis of muscle fibers indicates severe damage rather than atrophy due to disuse; it requires more acute injury scenarios, such as trauma or ischemia, not the post-surgical state characterized by more gradual atrophy due to lack of use. Therefore, increased protein degradation accurately explains the underlying mechanism of muscle loss in this context.