Many people living with Multiple Sclerosis (MS) describe their legs as feeling "weak" when they are actually stiff—or "stiff" when weakness is making movement difficult. Because these symptoms often occur together, it can be hard to tell them apart.

Understanding the difference is important because muscle weakness and spasticity have different causes and may respond to different treatments.

What Is Muscle Weakness?

Muscle weakness occurs when the muscles cannot generate their normal amount of force.

In MS, this usually happens because damage to the myelin disrupts communication between the brain and the muscles. Even though the muscles themselves may be healthy, the nerve signals that control movement become slower, weaker, or interrupted.

Common signs of muscle weakness include:

• Legs that feel heavy or difficult to lift

• Difficulty climbing stairs

• Trouble standing up from a chair

• Reduced grip strength

• Fatigue during activities that were previously easy

• A feeling that the muscles "won't respond"

  
  

Weakness often becomes more noticeable after physical activity or during periods of fatigue, illness, or heat exposure.

What Is Spasticity?

Spasticity is different.

Instead of muscles being unable to contract, the muscles become overactive because the nerve signals that normally help them relax have been disrupted.

This results in increased muscle tone, stiffness, tightness, or involuntary muscle spasms.

Common signs of spasticity include:

• Tight or rigid muscles

• Resistance when bending or straightening a limb

• Sudden muscle spasms or cramps

• Legs that seem to "lock" while walking

• Difficulty relaxing muscles, even while resting

  
  

Spasticity can fluctuate from day to day and is often influenced by fatigue, stress, infections, heat, prolonged sitting, or poor sleep.

Can You Have Both?

Yes—and many people with MS do.

A leg may feel weak because it cannot generate enough force, while at the same time feeling stiff because the muscles resist movement.

For example, you may struggle to lift your leg because of weakness, but once you begin walking, muscle tightness makes movement even more difficult.

This combination is one reason walking can feel both heavy and stiff.

Why the Difference Matters

Although weakness and spasticity often occur together, they are managed differently.

Spasticity may improve with:

• Stretching

• Physical or occupational therapy

• Range-of-motion exercises

• Medications such as baclofen or tizanidine (when appropriate)

• Botulinum toxin injections for selected muscles

  
  

Muscle weakness may improve with:

• Strengthening exercises recommended by a physical therapist

• Balance and gait training

• Functional training for everyday activities

• Energy conservation strategies

• Assistive devices when needed

  
  

Understanding whether weakness, spasticity, or both are contributing to your symptoms can help you and your healthcare team develop a more effective treatment plan.

When Should You Contact Your Healthcare Provider?

Speak with your healthcare provider if you notice:

• New or worsening muscle weakness

• Increasing muscle stiffness or spasms

• More frequent falls

• Painful muscle tightness

• Symptoms that interfere with walking, sleep, or daily activities

  
  

New or rapidly worsening weakness should always be evaluated promptly, as it may represent a relapse or another medical condition requiring treatment.

Final Thoughts

Although muscle weakness and spasticity can feel similar, they are not the same symptom.

Weakness makes it harder for muscles to generate force.

Spasticity makes it harder for muscles to relax.

Many people with MS experience both at the same time, making movement feel heavy, stiff, and more tiring than usual.

Understanding the difference can help you better recognize your symptoms, communicate with your healthcare team, and find management strategies that are tailored to your individual needs.

💬 Do you experience muscle weakness, spasticity, or both? What situations seem to make your symptoms better—or worse? Share your experiences with the community below.