Causes of Muscle Mass Loss

Key Takeaways:

• Loss of muscle mass (muscle atrophy) can be a result of aging or lifestyle habits, like being inactive or eating a poor diet.

• Muscle loss can also point to hormone abnormalities or underlying health conditions.

• Sudden or unexplained muscle loss calls for medical evaluation, which may include blood tests.

• Self-care practices make a difference in protecting and rebuilding muscle at every age.
  

Loss of muscle mass, also called muscle wasting or atrophy, can happen gradually as part of getting older or more suddenly due to underlying medical conditions. Other factors can contribute, like moving very little every day (being sedentary) or not getting enough nutrients (malnutrition).

For men, losing muscle mass can feel discouraging, especially when you’re not sure what’s causing it.

If you’re noticing unexplained changes in body composition, such as sudden muscle mass loss, seek medical attention to understand what’s going on underneath — and what to do next.

First, let’s look at some of the more common causes of loss of muscle mass in men.

1. Age-Related Muscle Loss

The medical term for age-related muscle loss is sarcopenia. It’s the progressive loss of muscle mass and strength that happens as guys get older.

Sarcopenia causes muscle atrophy and weakness. Though it’s primarily an age-related condition, factors like a poor diet and lack of physical activity also contribute.

Since sarcopenia affects your entire musculoskeletal system, it’s a significant contributor to overall weakness (frailty). It also increases the risk of falls and fractures. 

This condition becomes more common as guys reach age 60 and can affect up to  half of men 80 and older.

2. Hormone Changes

With age, testosterone levels gradually fall. Growth hormone also declines, but its impact in healthy adults is smaller. This has a direct effect on muscle mass.

Testosterone plays a central role in how the body builds and repairs muscle fibers (muscle protein synthesis).

After around age 35, testosterone levels in men start to gradually decline by about 1 percent per year on average. By the time you’re 50 or 60, this cumulative effect can significantly reduce your body’s ability to build and maintain muscle.

Lower testosterone levels (aka “low T”) are also linked to:

• Fatigue

• Decreased strength

• Feeling less motivated to exercise

All of these can contribute to further muscle mass loss.

Lower growth hormone with age can modestly affect body composition and recovery. But exercise and diet have a much bigger impact.

→ Learn more: The Testosterone Effect on Body Composition

3. Lifestyle Factors

Maintaining healthy habits can look a little different as you get older. But they’re still essential for supporting overall wellness, mobility, strength, and longevity. While some loss of muscle mass is part of getting older, everyday habits have a major influence — regardless of age. 

For instance, muscles follow a “use it or lose it” rule. When someone is sedentary — whether due to a desk job, lack of exercise, or extended bed rest after surgery or illness — muscle fibers that aren’t regularly being used begin to shrink.

Even short periods of disuse can lead to noticeable losses in strength, particularly in the legs.

Besides physical activity, nutrition is critical for muscular strength. Protein is widely known as “the building block of muscle,” and without enough of it, your body can’t effectively repair or maintain muscle tissue. 

Older adults are especially vulnerable to developing nutrient deficiencies. Not eating enough calories and not consuming enough foods with essential vitamins and minerals further weaken the body’s ability to preserve lean muscle.

4. Chronic Diseases

Having ongoing medical conditions can put extra stress on your body. This can contribute to muscle loss or wasting. For example:

• Cancer. Cancer can cause cachexia, a condition where the body rapidly loses fat and muscle. It’s often defined as more than 5 percent unintentional weight loss in 12 months or less with a chronic illness.

• Diabetes. If your blood sugar levels aren’t monitored and controlled well, this can lead to nerve and blood vessel damage that affects muscle function and repair.

• Kidney and liver disease. These organs are key players in your metabolism, including how your body breaks down and uses nutrients. When they’re not working as well as they should be due to disease, it can contribute to muscle breakdown.

• Heart failure and lung disease. Chronic heart or lung conditions make it harder for your body to get the oxygen it needs. This can lead to fatigue and weakness, making exercise more challenging.

• Rheumatoid arthritis (RA). RA is an autoimmune disease with chronic joint inflammation. It can limit physical activity and encourage muscle wasting.

With chronic illness, muscle wasting is often both a symptom and a factor that worsens quality of life, reducing muscle strength and recovery.

5. Neurological and Genetic Causes

In some cases, serious neurological or genetic causes are at the root of the issue.

These disorders mess with the communication between nerves and muscles or directly damage muscle fibers:

• Amyotrophic lateral sclerosis (ALS). ALS (Lou Gehrig’s disease) is a progressive neurodegenerative disorder that destroys motor neurons, the nerve cells that control muscle movement. Over time, this results in severe muscle atrophy.

• Muscular dystrophy. Muscular dystrophies are a group of inherited genetic disorders in which critical muscle proteins are either missing or not working properly. Over time, muscle fibers break down and are replaced with fat and scar tissue, causing severe weakness.

• Multiple sclerosis (MS). MS is an autoimmune disease where the immune system attacks the protective membrane around nerve fibers in the brain and spinal cord. Although MS primarily affects nerves, the resulting weakness and physical inactivity can cause muscle wasting.

• Spinal muscular atrophy (SMA). SMA is a genetic condition that affects motor neurons in the spinal cord. Without signals from these neurons, muscles don’t develop normally and gradually shrink.

Unlike the age-related and lifestyle-driven factors of muscle loss, these types of health conditions aren’t reversible (though some autoimmune conditions like MS may go into remission). However, newer treatments and physical therapy can slow their progression and improve strength.

Early diagnosis, supportive therapies, and, in some cases, newer medications can slow their progression and help maintain muscle mass and physical function.

Muscle mass loss may either appear gradually over time, like with age- and lifestyle-related reasons, or it could onset more suddenly. If you’re experiencing the latter, this indicates a more serious underlying cause.

Rapid muscle mass loss is a red flag that calls for medical evaluation. It shouldn’t be dismissed as a normal part of aging.

Potential causes of sudden loss of muscle mass include:

• Severe illness or infection. Hospitalization, sepsis, or systemic illness (affecting the whole body) can trigger fast muscle breakdown.

• Endocrine disorders. This includes sudden hormone imbalances (thyroid disease, diabetes, a sudden drop in testosterone, etc.).

• Cancer and cachexia. Rapid muscle wasting can happen due to metabolic changes from cancer and resulting cachexia.

• Nerve injury. Damage to a spinal cord or major nerve can quickly weaken a limb.

• Medication side effects. Long-term or high-dose corticosteroid use can lead to accelerated muscle loss.

GLP-1 Muscle Mass Loss

Glucagon-like peptide-1 (GLP-1) receptor agonists — medications like semaglutide and tirzepatide — can contribute to loss of muscle mass. These drugs promote weight loss by reducing appetite and slowing digestion, but part of the weight lost includes lean tissue, not just fat.

To protect lean mass while using GLP-1 medication, healthcare providers recommend adequate protein intake, resistance exercise, and gradual (rather than rapid) weight reduction.

What to Do If You Notice Sudden Muscle Mass Loss

Take note of whether your muscle mass is in one place (localized) or all over your body (generalized). Localized muscle loss, such as in one of your arms or legs, could be a nerve injury or a localized disorder. Muscle loss that’s not pinpointed to one area is more often related to a systemic issue.

Warning signs of sudden muscle loss to take seriously:

• Loss of muscle mass that develops in a short timeframe (weeks, not years)

• Weakness that interferes with daily tasks (climbing stairs, standing, lifting)

• Noticing related symptoms, such as fatigue, unexplained weight loss, pain, numbness, or problems finding your balance

Sudden muscle loss isn’t normal. If you think you’re experiencing it, get in touch with a healthcare provider right away.

Since muscle wasting can have many different causes, you need a proper medical evaluation to figure out what’s going on in your body.

Once an underlying condition is identified, it can be treated or managed. In some cases, this might mean slowing or reversing muscle loss.

A thorough medical evaluation will use various approaches to diagnose muscle loss.

Medical History and Physical Exam

The evaluation usually begins with your provider asking lots of questions about your personal and family health history. They might ask about:

• The onset and pace of muscle loss to know whether it’s been gradual or sudden

• Where you’re experiencing muscle loss

• Related symptoms, like weakness, fatigue, numbness, or unexplained weight loss

• Your current list of medications

• Your lifestyle habits, including what your diet looks like, the physical activity you’re getting, whether you smoke, and how often you drink alcohol

Next, your provider will do a physical exam to look for visible signs of muscle atrophy and test your reflexes, muscle strength, balance, and coordination.

Blood Testing for Loss of Muscle Mass

Blood tests can provide information as to what’s going on with your body and why you’re experiencing muscle decline.

Your provider might order lab tests to check for:

• Hormone levels. For men, these often include testosterone, thyroid hormones, cortisol, and growth hormone to check for endocrine imbalances.

• Nutritional markers. Knowing your vitamin B12, folate, iron, and protein status can help rule out specific nutrient deficiencies.

• Inflammatory markers. C-reactive protein (CRP) may help identify chronic inflammation or an underlying autoimmune disease.

• Metabolic function. Blood sugar, kidney, and liver function panels can help your provider evaluate how well your body processes nutrients and calories (energy) from food.

→ Read: What Blood Test Should I Get?

Imaging and Specialized Studies

In some cases, your medical provider might want to do additional imaging or testing, such as:

• Magnetic resonance imaging (MRI) or computerized tomography (CT) scans. These can detect structural issues in muscles or nerves.

• Electromyography (EMG). This measures electrical activity in muscles to assess nerve-muscle communication and muscle function.

• Nerve conduction studies. These can evaluate whether muscle loss is linked to nerve damage.

• Muscle biopsy. A muscle tissue sample may be ordered if your provider suspects a rare muscular disease. But this is less common.

Since muscle loss can result from something as common as inactivity or as serious as cancer, proper medical evaluation and testing is the only way to find the true cause.

Once you and your provider can pinpoint where your muscle mass loss is stemming from, this opens the door for targeted treatment options.

The right treatment approach for muscle mass loss depends on the underlying cause. Once your provider identifies what’s going on in your body, you can create a plan together that aligns with your needs and goals.

Exercise and Physical Therapy

Movement can be therapeutic regardless of the cause of muscle loss. But the type, frequency, and intensity of physical activity should be tailored to your abilities and fitness level.

Here’s what can support rebuilding muscle fibers and overall muscle health:

• Resistance training. Strength training is the most effective way to stimulate muscle growth, especially when weakness is caused by disuse. It doesn’t have to be intense or involve heavy weights — bodyweight exercises, lifting light weights, or using resistance bands can help rebuild and strengthen muscle.

• Aerobic activity. Cardio exercise supports blood circulation, energy, and overall health. It’s best used in combination with strength training. Swimming, walking, jogging, playing tennis, cycling, or doing martial arts are all great options.

• Physical therapy (PT). For men recovering from injury, illness, or bed rest, physical therapy can help retrain weak muscles safely and prevent further atrophy. PT is an essential piece of managing neurological conditions.

Nutrition Support

What you eat and how you nourish your body are extremely important for supporting your muscular health and physical capabilities.

Consider working with a registered dietitian or a healthcare professional for personalized recommendations, especially if you have an underlying medical condition.

Here’s what to think about when eating for muscle repair, muscle building, and general physical health:

• Getting enough protein. Most guys get more than enough protein. But older men and those losing muscle might need more. Our protein calculator can help you figure out how many grams you need per day.

• Adequate caloric intake. Under-eating, which is common among older men, speeds up muscle breakdown and can set you up for nutrient deficiencies.

• Prioritizing key nutrients. Calcium, magnesium, omega-3 fatty acids, and B vitamins (especially B12 and folate) support muscle and nerve function. If you’re deficient, supplementation can make a big difference.

• Specialized diets. For chronic illnesses (like diabetes or heart and kidney disease), a nutrition plan from a dietician or healthcare provider might aim to balance protein needs with organ health.

Hormone Health Support

If your muscle loss has to do with abnormal hormone levels, your provider might recommend:

• Testosterone replacement therapy (TRT). If testing confirms clinically low testosterone, TRT under medical supervision may improve muscle mass and strength.

• Thyroid or cortisol management. If a medical disorder is throwing thyroid hormones askew or you have abnormal cortisol levels, correcting these can help stabilize muscle metabolism.

→ Read: Hims Guide to Testosterone Replacement Therapy

Other Supportive Measures for Loss of Muscle Mass

If you have a specific medical condition affecting muscle health — such as a neurological disorder, cachexia, or chronic kidney disease — your healthcare team will prescribe a personalized treatment plan tailored to these needs.

These supportive measures can be helpful in these cases:

• Occupational therapy (OT). OT helps people with physical challenges adapt their daily routines and maintain independence.

• Pain and fatigue management. Medications, stress-management practices (like meditation, yoga, journaling, or breathing techniques), and other lifestyle changes (good sleep, nutrition, and movement) can help support overall well-being, making it easier to stay active.

• Regular monitoring. You might need follow-up blood work, strength testing, and body composition scans to help track your progress. That way, your provider can adjust your treatment if needed.

Muscle loss can feel discouraging, especially when it’s interfering with everyday life. But with the right combination of exercise, nutrition, and medical care, significant improvements are possible at any age.

While medical evaluation and treatment are critical, daily self-care plays a powerful role in protecting and rebuilding muscle health.

Many of the most effective strategies are simple, practical steps you can integrate into your routine:

• Move your body daily. Aim for at least 30 minutes of regular exercise, mixing strength, aerobic, and balance movements.

• Pay attention to protein. Include lean protein sources at every meal and snack. Think eggs, tofu, beans, poultry, lentils, and fish.

• Fuel your body adequately. Don’t skip meals — it can set you up for inadequate calorie intake or a nutrient deficiency over time. Eat a variety of nutrient-dense foods (fruits, vegetables, nuts, seeds, whole grains, and lean proteins).

• Prioritize your rest. Try to get 7 to 9 hours of quality sleep each night to support recovery and energy levels. Address sleep hygiene, such as following a set sleep-wake schedule and avoiding disruptors close to bed (like screens, alcohol, and caffeine).

• Manage stress. Relaxation methods, like deep breathing, meditation, light stretches, or journaling, can help calm your nervous system and minimize the harmful effects of stress on your body.

• Stay hydrated. Dehydration can mess with performance and recovery. Sip on water throughout the day to stay hydrated.

• Be proactive. If you notice changes in your strength or muscle size, reach out to your provider. Even if you feel otherwise healthy, it’s important to schedule regular preventive wellness check-ups.

Loss of muscle mass can happen gradually with age or suddenly due to underlying illness, but it should never be ignored.

Possible causes of muscle loss vary, which is why proper evaluation is so important. If you notice unexplained weakness or sudden changes, reach out to your healthcare provider.

Below are answers to common questions guys have about loss of muscle mass.

What causes loss of muscle mass in legs?

Loss of muscle mass in the legs is often due to inactivity, aging (sarcopenia), or long periods of bed rest. It may also result from nerve injuries, poor circulation, or chronic illnesses like diabetes or multiple sclerosis. If the muscle loss appears suddenly or only in one leg, see a healthcare professional to rule out nerve or blood flow (vascular) issues.

Can hormonal changes cause loss of muscle mass?

Yes. Declining testosterone and growth hormone levels with age reduce the body’s ability to build and maintain muscle. These hormonal changes contribute to sarcopenia (age-related loss of muscle mass and strength), particularly in men over 50.

When should I worry about loss of muscle mass?

You should be concerned if you notice sudden or unexplained loss of muscle mass, especially if it’s localized (for example, only in the legs) or accompanied by weakness, fatigue, or weight loss. In these cases, prompt medical evaluation with blood tests and physical exams is essential to identify the underlying cause.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards.