It is natural to think of muscle as the machinery that moves the skeleton, but that framing badly undersells it. Skeletal muscle is the largest organ in most bodies by mass, and it functions as a metabolic and endocrine organ whose health radiates outward to the brain, the immune system, and the regulation of blood sugar.
The glucose disposal system
After a meal, muscle is the largest site for clearing glucose from the bloodstream, taking it up and storing it as glycogen or burning it for fuel. The more muscle a person has, and the more it is used, the more capacity the body has to manage carbohydrate without blood sugar swings and chronically elevated insulin. Losing muscle with age shrinks this glucose sink at exactly the time the body tends to become less insulin sensitive, compounding the problem.
Strength and survival in the data
Across large studies, higher muscle strength and greater muscle mass are associated with lower all-cause mortality. Grip strength, a simple and cheap measure, turns out to be a surprisingly powerful predictor of future health and survival, often outperforming more elaborate tests.
Evidence Check: Higher muscle strength and mass are associated with lower all-cause mortality across large studies. Grip strength is a surprisingly strong predictor of longevity.
Myokines: muscle as a chemical broadcaster
Contracting muscle releases signaling molecules called myokines that travel through the body and influence distant organs. These molecules participate in conversations with fat tissue, the immune system, and the brain, and are part of how exercise produces benefits far beyond the muscle itself — including effects on mood, cognition, and inflammation. Working muscle is in constant beneficial dialogue with the rest of the system.
Sarcopenia and the cost of doing nothing
Left unaddressed, muscle mass and strength decline progressively with age — a process called sarcopenia that accelerates after midlife. Declining muscle erodes the glucose disposal system, reduces the myokine signaling that supports the rest of the body, and eventually undermines the basic functional capacity to climb stairs, carry groceries, and recover from a fall. The encouraging counterpoint: muscle remains responsive to training at every age, so the decline is substantially a function of disuse.
Protein as the partner to training
Building and preserving muscle is a partnership between a stimulus and raw material. Resistance training signals the body to build muscle, but without adequate protein the signal outruns the supply. This becomes more important with age, as the muscle-building response to a given amount of protein becomes blunted — arguing for higher total daily intake spread across meals rather than concentrated in one.
Disclaimer: Begin or change an exercise program sensibly; consult a doctor first if you have cardiovascular issues.