Mitochondrial dysfunction is the primary cause of age-related decline in skeletal muscle.

The Short Version

The scientific literature does not support singling out mitochondrial dysfunction as "the primary cause" of age-related skeletal muscle decline. While multiple peer-reviewed reviews describe mitochondrial dysfunction as an important contributor and sometimes hypothesize it as an upstream initiator, the broader evidence base consistently characterizes sarcopenia as multifactorial—driven by denervation, neuromuscular junction failure, chronic inflammation, hormonal changes, and anabolic resistance alongside mitochondrial impairment. At least one high-authority source explicitly identifies denervation, not mitochondrial dysfunction, as the dominant driver in very old muscle.