Video

By Eugene Capitano, BA, BSc, DC, DAc, MSc, ACSM-CPT, ACSM-EIM
Chiropractor | Functional Wellness Specialist | Clinical Researcher

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Most people think of skeletal muscle as the tissue that helps us move, lift, and stay active. But muscle is much more than a mechanical system. It is one of the body’s largest metabolic organs, a major site for glucose disposal, a reservoir for amino acids, a home for mitochondria, and a source of signals that communicate with other tissues throughout the body.

Losing muscle is therefore not only about becoming smaller or weaker. It can reduce the body’s ability to manage blood sugar, recover from illness, preserve mobility, and remain independent.

MUSCLE HELPS CONTROL BLOOD SUGAR

After a meal, skeletal muscle is responsible for most insulin-stimulated glucose uptake. In practical terms, muscle acts as a large metabolic “sink,” helping move glucose out of the bloodstream so it can be stored as glycogen or used for energy.

Muscle mass matters because more active tissue provides greater potential capacity for glucose storage and metabolism. However, size alone is not enough. Glucose uptake also depends on insulin sensitivity, blood flow, recent muscle contraction, mitochondrial function, and the amount of fat that has accumulated within the muscle.

This explains why exercise can improve blood sugar control even before someone gains noticeable muscle. Contracting muscle can increase glucose uptake through pathways that are partly independent of insulin.

SARCOPENIA AND DYNAPENIA ARE DIFFERENT

Sarcopenia is commonly described as age-related muscle loss. Modern clinical definitions, however, place increasing emphasis on strength and physical performance, not muscle mass alone.

Dynapenia refers specifically to the age-related loss of strength and power. This distinction matters because strength often declines faster than muscle size. Two people can have a similar amount of lean tissue while having very different levels of strength, balance, walking ability, and independence.

Muscle health includes several related but distinct dimensions:

Muscle quantity is how much lean or contractile tissue is present.

Muscle quality is how effectively that tissue functions.

Strength is how much force the neuromuscular system can produce.

Power is how quickly that force can be expressed.

Physical performance is how well the body completes real-life tasks.

A body-composition scan may estimate how much lean tissue you have, but it cannot tell you how well that muscle works.

WHY STRENGTH AND POWER MATTER SO MUCH

Low strength and poor physical performance are consistently associated with greater risks of disability, hospitalization, and all-cause mortality. These findings do not prove that weakness directly causes death, but they show that strength is a powerful marker of overall physiological reserve.

Lower-body strength and power are especially important because everyday life requires the ability to generate force quickly. Rising from a chair, climbing stairs, crossing a street, recovering from a loss of balance, and preventing a fall all require more than muscle size. They also require speed, coordination, nerve function, and rapid force production.

This is why leg strength, walking speed, chair-rise ability, and sit-to-stand power may reveal more about future independence than muscle mass alone.

WHY MUSCLE MASS STILL MATTERS

The stronger relationship between strength and long-term outcomes does not mean muscle mass is unimportant.

Muscle mass provides metabolic and physiological infrastructure. It contributes to glucose disposal, glycogen storage, amino-acid reserve, force-producing capacity, mitochondrial volume, and resilience during inactivity, immobilization, or hospitalization.

The body does not maintain a separate storage depot for protein. During illness, surgery, infection, fasting, or inadequate nutrition, amino acids can be released from skeletal muscle to support immune activity, wound healing, liver protein production, and other essential functions.

Greater muscle reserve may provide a buffer during illness or inactivity. However, it does not completely prevent rapid muscle loss. Older adults can lose muscle quickly during

hospitalization, bed rest, immobilization, or even a major reduction in daily steps, and recovery is often slower than in younger adults.

MUSCLE QUALITY CONNECTS MASS TO FUNCTION

Muscle quality helps explain why some people are much stronger, more mobile, or more insulin-sensitive than others with a similar amount of lean mass.

Muscle quality can be affected by fat infiltration within the muscle, loss of motor nerves, reduced neural activation, atrophy of fast muscle fibres, impaired blood flow, mitochondrial dysfunction, connective-tissue changes, chronic disease, pain, and inactivity.

This is why muscle health should not be judged by appearance, body weight, or a scan alone. A better assessment combines muscle quantity with a functional measure such as grip strength, chair-rise ability, gait speed, or lower-body strength.

MUSCLE IS ALSO A SIGNALING ORGAN

Contracting muscle releases signaling molecules that communicate with the liver, fat tissue, bone, immune system, and brain. These signals are often called myokines or exerkines.

They help coordinate fuel use, tissue repair, inflammation, and adaptation to exercise. Research in this area continues to evolve, and individual molecules should not be promoted as if they independently prevent disease.

The larger message is simpler: active muscle communicates with the rest of the body. Preserving muscle without using it is not biologically equivalent to maintaining a regularly contracting, metabolically active muscle organ.

AGING, INACTIVITY, AND ANABOLIC RESISTANCE

As people age, muscle often becomes less responsive to the usual anabolic signals from protein and exercise. This is called anabolic resistance.

Anabolic resistance is not caused by age alone. Physical inactivity, illness, inflammation, insulin resistance, inadequate protein, low energy intake, reduced blood flow, and chronic disease can all contribute.

Even short periods of reduced activity can lower muscle protein synthesis and accelerate the loss of lean tissue. Resistance exercise is one of the strongest countermeasures because it stimulates muscle protein synthesis and increases the muscle’s sensitivity to dietary amino acids.

Protein provides the building material. Resistance exercise provides the signal and mechanical reason to use it.

THE ROLE OF PROTEIN

The standard adult protein recommendation of 0.8 grams per kilogram of body weight per day is intended to meet the basic needs of most healthy adults. It is not necessarily the ideal amount for preserving muscle in every older or physically active person.

Expert groups commonly recommend higher protein intakes for healthy older adults, with additional consideration during illness, frailty, or rehabilitation. Protein intake at individual meals may also matter because muscle protein synthesis responds to separate feeding events throughout the day.

Leucine helps initiate anabolic signaling, but leucine alone cannot build muscle. The complete range of essential amino acids is needed to supply the raw material for new protein synthesis.

The goal is not to chase one universal “magic” number. The practical priority is to avoid chronically low total protein intake and meals that repeatedly contribute too little protein to daily needs.

THE MOST COMPLETE STRATEGY

No single type of exercise addresses every part of muscle health.

Progressive resistance training is the most direct way to preserve or increase strength and lean tissue.

Power training, introduced appropriately and safely, helps maintain the ability to produce force quickly.

Aerobic exercise supports mitochondrial function, circulation, insulin sensitivity, and cardiorespiratory fitness.

Balance and task-specific training support mobility and fall prevention.

Adequate protein and energy intake provide the material needed for recovery and adaptation.

The best approach is not cardio versus weights. It is a combined strategy that preserves muscle quantity, improves tissue quality, maintains strength and power, and keeps muscle regularly active.

THE BOTTOM LINE

Muscle mass is metabolic infrastructure. Muscle quality determines how effectively that infrastructure works. Strength and power show whether the neuromuscular system can produce useful force, while physical performance shows whether the whole body can translate that capacity into everyday life.

Healthy aging is not simply about carrying more muscle. It is about maintaining muscle that is metabolically active, neurologically connected, strong, fast, and regularly used.