Do you lose muscle when sick? An expert breakdown

September 27, 2025 •

5 min read

According to research from the Salk Institute, muscle loss, or 'wasting,' is a common symptom during infection, and surprisingly, may even aid the body's fight against illness. This reveals a complex and often misunderstood relationship between your immune system and muscle mass, leaving many to wonder, do you lose muscle when sick?

Quick Summary

Yes, it is possible to lose muscle when you are sick, but the extent of muscle loss depends on the severity and duration of the illness. Mild sicknesses cause minimal loss, while severe, prolonged infections can lead to significant muscle atrophy due to reduced activity, poor nutrition, and systemic inflammation.

Key Points

Severity is key: You are unlikely to lose significant muscle mass from a mild, short illness like a cold, but prolonged, severe infections can cause rapid and noticeable atrophy.
Immune response requires energy: When your body fights infection, its energy demands increase. If your nutritional intake drops, your body may break down muscle protein for fuel.
Immobility is a major factor: Even a few days of bed rest can initiate disuse atrophy. For severe illness, this effect is much more pronounced and rapid.
Age affects vulnerability: Older adults naturally have lower muscle reserves and are more susceptible to rapid muscle loss during periods of inactivity.
Prioritize protein and rest: Support your body during sickness by maintaining protein intake through easy-to-digest sources and prioritizing rest to allow your immune system to work efficiently.
A gradual return is best: Post-sickness recovery requires a slow and steady return to exercise, focusing on consistency and listening to your body to prevent setbacks and safely rebuild muscle.

Understanding the body's response to illness

When your body is fighting off an illness, your immune system shifts into high gear. This intense metabolic process requires a significant amount of energy. If your caloric intake is reduced—a common side effect of a suppressed appetite—your body seeks alternative fuel sources. Your muscles, which are metabolically active and store glycogen, can become a target for this energy demand.

The mechanism of muscle atrophy

Muscle atrophy is a process where the body breaks down more protein than it builds. During illness, several factors accelerate this process:

Inflammatory response: Your body releases pro-inflammatory cytokines to fight infection. While beneficial for your immune system, these same compounds can interfere with the signaling pathways that promote muscle protein synthesis and increase pathways that cause breakdown.
Immobility and reduced activity: Even a few days of bed rest can lead to disuse atrophy. For every day spent in bed, your muscles are not receiving the mechanical stress needed to maintain mass. Research shows that healthy individuals on bedrest can lose about 0.5% of their muscle daily.
Nutritional deficiencies: A lack of appetite or difficulty keeping food down can lead to a caloric and protein deficit. Without sufficient protein, the building blocks for muscle repair and maintenance are limited, further encouraging muscle breakdown.

Severity of illness matters

Not all sicknesses are created equal when it comes to muscle loss. The impact is heavily influenced by the illness's intensity and length.

Mild vs. Severe Illness: A Comparison


Factor	Mild Illness (e.g., common cold)	Severe Illness (e.g., flu, critical infection)
Sickness Duration	Typically 3-7 days	Often 10+ days, possibly longer
Activity Level	May be slightly reduced, but not complete bed rest	Significant or complete immobilization/bed rest
Nutrition	Appetite may be lower, but usually maintained	Severely reduced intake, potential malnourishment
Inflammatory Response	Short-lived and localized	Systemic and sustained
Protein Breakdown	Minimal impact on muscle protein synthesis	Significant increase in protein catabolism
Muscle Loss	Minimal; often just temporary strength reduction	Substantial, with studies showing rapid loss
Recovery Time	Quick rebound once healthy	Longer, more structured recovery needed

Factors influencing muscle loss

While the severity of illness is the primary driver, other factors also play a role in how much muscle you might lose.

Age

Older adults, who naturally experience sarcopenia (age-related muscle loss), are more susceptible to rapid muscle wasting during periods of inactivity caused by illness. Having lower muscle reserves to begin with, a bout of sickness can have a more pronounced effect on their overall muscle mass.

Pre-existing fitness level

Your baseline fitness and health also affect your body's resilience. An already fit and healthy person with a robust immune system and good muscle mass will likely experience minimal and quickly reversible muscle loss during a short illness. Conversely, someone with a less active lifestyle or underlying health issues may be at greater risk.

Medications

Certain medications used to treat illnesses can have side effects that contribute to muscle loss. Examples include corticosteroids, which are often prescribed to reduce inflammation but can also cause muscle weakness over time.

How to minimize muscle loss when sick

While rest is crucial for recovery, you can take proactive steps to mitigate muscle loss.

Focus on nutrition: When your appetite is low, prioritize protein intake through easily digestible sources like broth, Greek yogurt, eggs, or a high-quality protein shake. Aim for 1.2 to 2.2 grams of protein per kilogram of body weight, if you can stomach it. Staying hydrated is also key. Consider adding electrolytes to your water.
Gentle movement: For mild illnesses, light bodyweight movements or short, gentle walks can help maintain blood flow and prevent disuse atrophy. For more severe cases, simply getting up and walking a few steps or moving from the bed to a chair can make a difference.
Prioritize rest: Don't push yourself to work out intensely. Your body needs energy to fight the illness, and overexertion can prolong your recovery. Adequate sleep and rest are critical for your immune system to function optimally.

The recovery process: regaining lost muscle

Once you're on the mend, a gradual return to your routine is essential. The phenomenon of "muscle memory" is on your side, meaning your body can rebuild lost muscle more efficiently than it built it the first time.

Ease back into activity: Begin with lower intensity and volume. Listen to your body and don't try to lift your pre-sickness weights on day one. Slowly increase the intensity as you feel stronger.
Focus on multi-joint movements: Prioritize exercises that use multiple muscle groups, such as squats, rows, and presses, to maximize your rebuilding efforts.
Ensure sufficient protein and calorie intake: During the recovery phase, your body needs extra resources for repair and growth. Continue prioritizing protein and ensure you are eating enough calories to support muscle building.
Stay consistent: Regular, consistent training is more effective than trying to rush the process. Patience is a virtue in recovery.

The science behind muscle wasting

Recent research is shedding light on the intricate relationship between the immune system and muscle tissue. For instance, a study at the Salk Institute, published in Cell Metabolism, showed that in mice with infection, muscle loss was an active, regulated immune response rather than a side effect, potentially providing fuel for a stronger immune defense. Understanding these deeper mechanisms can lead to more targeted therapies for patients suffering from significant muscle wasting.

For more detailed information on preventing muscle atrophy in clinical settings, the National Institutes of Health (NIH) provides valuable resources. For example, the PMC site offers insights on disease-induced skeletal muscle atrophy.

Conclusion: take it slow and steady

While losing a noticeable amount of muscle during a mild, short-lived illness is unlikely, severe or prolonged sickness can lead to significant atrophy. The key takeaway is to support your body's immune function with adequate rest, proper nutrition, and hydration. When you're ready to get back to your routine, a slow and patient approach will ensure a safe and effective recovery, helping you regain your strength without risk of setback.

Frequently Asked Questions

The rate of muscle loss depends on the severity of the illness. For a mild sickness and a few days of inactivity, the loss is minimal. With severe, prolonged illness or hospitalization, rapid muscle atrophy can occur within 10-14 days due to prolonged bed rest and inflammation.

Complete prevention is difficult, as illness triggers a natural catabolic state. However, you can significantly minimize loss by maintaining adequate protein intake, staying hydrated, and incorporating very gentle movement if your body allows.

Start with a gradual return to exercise, focusing on multijoint movements and lighter weights. Prioritize sufficient protein and calorie intake to support muscle synthesis and allow for adequate rest between workouts. Your body's muscle memory will help accelerate the process.

Yes, if you can. A high-protein diet is crucial for supplying the amino acids needed for muscle maintenance and repair. If your appetite is low, focus on easy-to-digest sources like protein shakes, yogurt, or soft meats.

Muscle atrophy is the medical term for the wasting or thinning of muscle mass. While temporary loss during sickness is a form of atrophy, it is usually reversible through proper nutrition and exercise. It becomes a more significant concern in cases of prolonged or severe illness.

Not necessarily. Post-illness weakness often comes from fatigue, dehydration, and reduced energy stores, rather than permanent muscle loss. While some atrophy might occur, the feeling of weakness is often temporary and subsides as your body recovers.

Mild illness, such as a cold, typically doesn't cause significant muscle loss because it's short-lived and doesn't require extended bed rest. Severe illness, like a serious infection, involves a more intense inflammatory response and prolonged inactivity, leading to more substantial and rapid muscle atrophy.