Sarcopenia — the progressive, age-related loss of skeletal muscle mass and function — begins in the fourth decade and accelerates with each subsequent decade. Adults lose approximately 3–8% of muscle mass per decade after age 30, with acceleration after 60. The consequences compound: reduced basal metabolic rate, worsening insulin resistance, increased fall risk, decreased bone density (muscle contraction is the primary stimulus for bone remodeling), and loss of the functional reserve needed to survive acute illness.
Skeletal muscle is an endocrine organ. It secretes myokines — including IL-6, irisin, BDNF, and others — that have systemic effects on metabolism, inflammation, brain health, and cancer surveillance. Irisin, released during exercise, promotes white-to-brown fat conversion and crosses the blood-brain barrier, directly stimulating hippocampal neurogenesis. The cardiovascular, metabolic, and cognitive benefits of exercise are substantially mediated by these myokine signals.
Progressive resistance training is the primary intervention to build and preserve muscle mass. The principle is progressive overload — gradually increasing stimulus over time through heavier weights, more volume, or greater density. For general health, 2–3 sessions per week targeting major muscle groups is sufficient. Protein intake is a critical co-factor: 1.6–2.2 g/kg body weight per day is the range supported by meta-analyses for muscle protein synthesis optimization, with protein distribution across meals being more important than total intake alone.
Muscle mass should be assessed — not just assumed. DXA (dual-energy X-ray absorptiometry) provides the most accurate body composition measurement, including appendicular lean mass (ALM) normalized to height. Grip strength (measured by dynamometry) is a validated proxy for overall muscle strength and a significant predictor of functional outcomes, hospitalization risk, and all-cause mortality in multiple longitudinal studies. These measurements are available but rarely ordered in primary care.