As dogs age, many begin to slow down taking shorter walks, resting more often, and showing less interest in play. While this may look like “normal aging,” it often reflects a biological process called canine sarcopenia the progressive loss of muscle mass, strength, and endurance.

Research shows that dogs can lose up to 30% of their muscle mass by the time they reach senior years, and studies estimate that one in three senior dogs shows clinically significant muscle wasting. This decline isn’t just about weaker legs or less energy, it’s tied to metabolism, resilience against disease, and overall lifespan

What Happens Inside Aging Muscles

Muscle decline in older dogs is not simply the result of “wear and tear” It begins at the cellular level, where essential repair and energy processes start to falter.

1. Mitophagy Decline

In healthy muscles, mitophagy acts like a quality-control system, removing old and damaged mitochondria so new, efficient ones can take their place. With age, this clearance process slows, allowing dysfunctional mitochondria to accumulate. The result is energy delivery becomes inefficient, endurance drops, and dogs fatigue more quickly, even during short walks or mild play.

2. Mitochondrial Dysfunction

Energy for movement depends on mitochondrial biogenesis, the ability of muscle cells to produce new high-functioning mitochondria. In senior dogs, this process declines, leading to fewer “powerhouses” in each muscle cell. With less energy available, muscles tire rapidly, and recovery from even light exercise takes longer.

3. Reduced Autophagy

Autophagy is the cell’s internal recycling system, breaking down damaged proteins and clearing senescent (aged) cells that no longer function properly. When autophagy slows with age, waste products accumulate inside muscle fibers, triggering low-grade chronic inflammation. What we see outwardly slower movement, stiffness, or reluctance to exercise is really the reflection of deeper cellular wear, where muscles can no longer keep up with the body’s demands.

The Bigger Concern: Muscle Loss as a Driver of Other Syndromes

Muscle isn’t just for movement it’s the body’s largest metabolic organ. When dogs lose muscle, a cascade of health issues follows:

• Insulin Resistance and Metabolic Dysfunction

Muscle is the primary site of glucose uptake. With muscle loss, insulin sensitivity declines, leading to poor glucose control and systemic inflammation. This sets the stage for canine metabolic syndrome, characterized by weight gain, reduced energy, and increased disease risk.

• Obesity and Adiposity

As muscle declines, fat tissue increases to compensate. This imbalance contributes to joint stress, hormonal changes, and a chronic pro-inflammatory state.

• Liver Dysfunction

Excess fat deposition in the liver disrupts metabolic balance, causing oxidative stress and impairing detoxification further worsening fatigue and overall vitality.

• Frailty and Mobility Syndromes

Dogs with significant muscle loss are more prone to osteoporosis, arthritis, and frailty syndrome, where even daily activities like climbing stairs or rising from rest become a struggle.

Supporting Muscle Health in Senior Dogs

Humans aren’t the only species that need tailored nutrition as they age our senior dogs do too. As dogs get older, their metabolism alters, and they may struggle to maintain lean muscle. Studies report that senior dogs can lose around 10% of their lean body mass, while simultaneously gaining fat changes that are subtle but significant.

So what can help? High-quality protein is foundational. It supports muscle repair and maintenance especially crucial given the age-related imbalance where muscle breakdown begins to outpace synthesis. Alongside protein, nutrients that reduce inflammation can protect fragile muscle fibers and support recovery.

But nutrition alone isn’t enough. Aging muscles need movement to stay resilient. Even gentle, consistent activity like walking, swimming, or balance exercises can help sustain strength and flexibility. When paired with tailored physiotherapy or hydrotherapy, these routines offer powerful support for mobility and overall well-being.