Why Am I Losing Muscle Mass? Causes, Signs and Fixes
Most unexplained muscle loss comes from using your muscles less, getting older, or eating too little protein and energy. Less often, it's a sign of nerve damage, a hormone problem or another illness. The good news is that the common causes respond well to regular strength training and enough protein at each meal.
Maybe your legs look thinner after a few months at a desk job, or the stairs feel harder than they did last year. This guide is for anyone who has noticed that change and wants to know what's behind it and what to do next.
Key takeaways
- Disuse is the most common cause: muscles shrink when they aren't worked regularly, and this type can often be reversed with exercise and better nutrition.
- Age plays a part: Cleveland Clinic says age-related muscle loss (sarcopenia) starts in your 30s or 40s and speeds up between ages 65 and 80.
- Strength training is the main fix: adults should do muscle-strengthening activity on at least 2 days a week, according to the CDC.
- Protein matters at every meal: spreading protein across the day supports muscle repair.
- Some patterns need a doctor: loss that is fast, unexplained or worse on one side of the body should be checked.
What is muscle atrophy?
Muscle atrophy means the wasting or thinning of muscle tissue. MedlinePlus, the patient site of the U.S. National Library of Medicine, groups it into three types:
- Disuse (physiologic) atrophy: caused by not using muscles enough. It's common in people with seated jobs, limited mobility, long bed rest, or after a stroke or orthopedic injury. It can often be reversed.
- Pathologic atrophy: linked with aging, starvation and conditions such as Cushing disease, where the body has too much corticosteroid hormone.
- Neurogenic atrophy: the most severe type. It happens when the nerve that supplies a muscle is injured or diseased, and it tends to come on more suddenly.
Most people who notice gradual muscle loss are dealing with disuse, age-related change, or both. Neurogenic causes are less common but are the reason a doctor's check matters when the pattern is unusual.
What causes muscle loss?
Inactivity
Muscle responds to demand. When you stop asking it to work, through a desk-bound routine, a cast, an illness or a long recovery in bed, your body stops maintaining it. Legs often show it first because they do so much of the work of daily walking.
Aging and sarcopenia
Sarcopenia is the gradual, age-related loss of muscle mass, strength and function. Cleveland Clinic notes that people may lose up to 8% of their muscle mass per decade, and that the process speeds up between 65 and 80. With age, the body uses protein less efficiently, hormone levels such as testosterone and IGF-1 shift, and muscle fibers shrink in both size and number. It's common, but weakness shouldn't be written off as "just aging." Hormone questions can come up much earlier in life too, and our guide to low testosterone at 30 and whether to start TRT covers the options for younger men.
Not enough protein or energy
Muscle is rebuilt from the protein you eat. If your diet is low in protein, or you're cutting calories hard, your body has less material for repair. Fast or aggressive dieting without strength training is a common way people lose muscle along with fat. If you're on a very low-carb plan, our guide on whether the source of your calories matters explains how different diets affect body composition.
Medicines and medical conditions
MedlinePlus lists long-term corticosteroid therapy, malnutrition, burns, muscular dystrophy and other muscle diseases, osteoarthritis and rheumatoid arthritis as causes of muscle wasting. Cleveland Clinic adds that chronic conditions such as heart disease, diabetes and COPD raise the risk of sarcopenia. Nerve-related causes include spinal cord injury, nerve damage from diabetes, injury, toxins or alcohol, and diseases such as ALS and Guillain-Barré syndrome. If you've had Guillain-Barré and are now weighing jaw or cosmetic injections, our guide to toxin injections after Guillain-Barré covers the safety questions to raise first.
What are the early signs of muscle loss?
Muscle loss tends to creep up. Use this checklist to spot it:
- Arms, thighs or calves look smaller, or clothes fit differently there
- Getting up from a chair without using your arms feels harder
- Stairs, carrying shopping or opening jars takes more effort
- You walk more slowly or tire sooner
- Your balance feels less steady, or you've had a fall
- One hand, arm or leg looks thinner than the other
That last sign is worth special attention. MedlinePlus notes that unexplained muscle loss is often most noticeable when you compare one side of the body with the other.
How can you rebuild lost muscle?
1. Start strength training, even at home
Resistance training is the main way to slow and reverse disuse and age-related muscle loss. The CDC recommends that adults do muscle-strengthening activities on at least 2 days a week, working the legs, hips, back, abdomen, chest, shoulders and arms. That can mean weights, resistance bands, machines or your own body weight.
If you're starting from a low base, the NHS suggests simple moves such as sit-to-stands from a sturdy chair, mini squats while holding a chair back, calf raises, wall press-ups and biceps curls with filled water bottles. Start gently and add repetitions over time. For more ideas once you're comfortable, see these longevity exercises for a stronger life. When those feel easy, our simple strength training plan for beginners over 40 is a sensible next step.
2. Spread protein across your meals
Cleveland Clinic suggests about 20 to 35 grams of protein per meal for people with sarcopenia, from food and supplements if needed. Eggs, fish, poultry, dairy, beans, lentils and tofu all count. Think in meals, not just a daily total: a light toast-and-coffee breakfast often leaves a gap. Our simple muscle gain diet walks through easy ways to fill it. More isn't always better, though; if you have kidney disease or are tempted to go very high, read about the risks of too much protein and check with your doctor.
3. Move more between workouts
Two strength sessions a week work better when the rest of your week isn't spent sitting. The CDC also recommends 150 minutes of moderate aerobic activity, such as brisk walking, each week. Short walks after meals and standing breaks add up.
4. Recover well
Sore, tight muscles can make it tempting to skip sessions. Gentle mobility work helps some people stay consistent; this guide to using a massage ball for myofascial release covers simple techniques.
5. Treat the cause
If a medicine, hormone problem or illness is driving the loss, exercise alone may not be enough. A doctor can review your medicines (don't stop any on your own), look for underlying conditions, and refer you to a physical therapist. MedlinePlus notes treatment may include an exercise program, pool exercises, braces or splints, and other rehabilitation.
Which type is it? A quick comparison
| Type | Typical pattern | Usual next step |
|---|---|---|
| Disuse | Gradual, both sides, after less activity or bed rest | Strength training and protein |
| Age-related (sarcopenia) | Slow loss of strength and stamina over years | Strength training, protein at each meal, routine checkups |
| Neurogenic | Can be sudden, often one limb, may include numbness or tingling | See a doctor promptly |
When should you see a doctor?
Book an appointment if you notice any of the following:
- Muscle loss that is unexplained or has lasted a long time
- One limb clearly thinner or weaker than the other
- Numbness, tingling, pain, twitching or trouble swallowing or speaking alongside the weakness
- Unplanned weight loss
- Weakness that makes falls or daily tasks harder
- A long-term condition or medicine (such as steroids) that is known to affect muscle
Your provider may check your strength with simple tests such as grip strength, chair stands and walking speed, and may order blood tests or imaging. Cleveland Clinic notes there's no single test for sarcopenia, so expect a mix of questions and physical checks.
FAQ
Can you regain muscle mass after losing it?
Often, yes. MedlinePlus says disuse atrophy can often be reversed with exercise and better nutrition. Progress depends on your age, health and the cause. Regular strength training on at least two days a week, plus enough protein, is the usual starting point. Muscle lost from nerve damage is harder to recover and needs medical care.
At what age do you start losing muscle?
According to Cleveland Clinic, age-related muscle loss begins in your 30s or 40s and speeds up between 65 and 80. The pace varies a lot between people. Staying active, doing resistance exercise and eating protein at each meal can slow it down, even if you start later in life.
How fast can you lose muscle from inactivity?
It depends on how inactive you are and your starting point. Full bed rest or a limb in a cast causes faster loss than simply sitting more. Legs tend to show it first. If you're recovering from surgery or illness, ask your care team about safe movement as early as possible, as gentle activity helps limit the loss.
What to do next
- Try the chair test: count how many times you can stand up from a chair without using your arms in 30 seconds, and note it so you can track change.
- Schedule two short strength sessions this week, using body weight or bands.
- Add a protein source to the meal where you usually have the least, often breakfast.
- Book a doctor's visit if your loss is fast, one-sided or comes with numbness or pain.
This article is for general information and is not medical advice.
Last reviewed: October 2026.
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