Skeletal muscle is the largest metabolically active tissue in the human body. It is the primary site of postprandial glucose disposal, a major producer of anti-inflammatory myokines, the main determinant of resting metabolic rate, and a critical component of the hormonal environment that regulates body composition. The progressive loss of muscle mass that accompanies ageing, known as sarcopenia, is therefore not merely a fitness concern. It is a metabolic health emergency.
Muscle as the Primary Glucose Disposal Site
Approximately 80 percent of postprandial glucose is taken up by skeletal muscle. When muscle mass is low, glucose disposal capacity is reduced, necessitating higher insulin secretion to maintain blood glucose. This is a primary driver of the insulin resistance that progresses to type 2 diabetes. Building and preserving muscle mass is therefore the most powerful single intervention for preventing type 2 diabetes in adults at risk.
Myokines: Muscle as an Endocrine Organ
Muscle contraction releases signalling proteins called myokines into the circulation. IL-6 released from contracting muscle acts as an anti-inflammatory agent in the systemic circulation, reducing chronic low-grade inflammation. Irisin stimulates fat burning, improves insulin sensitivity, and has evidence for brain-derived neurotrophic factor production. Myostatin inhibits excessive muscle growth. These myokines explain why exercise has benefits that extend far beyond the mechanical function of the muscle itself.
The Mortality Evidence
Grip strength, a simple proxy for overall muscle mass and quality, is one of the strongest predictors of all-cause mortality in adults over 50. A landmark study in the Lancet involving over 130,000 participants across 17 countries found that low grip strength predicted cardiovascular mortality more strongly than systolic blood pressure. The data on muscle mass and longevity is, at this point, overwhelming.