Why Do Muscles Sometimes Struggle to Relax? Understanding Myotonia

Introduction: When Muscles Do Not Relax Normally

Have you ever wondered why someone might struggle to release their hand immediately after gripping an object, or experience stiffness when trying to move after a period of rest?

Muscle stiffness can occur for many reasons. However, when a muscle repeatedly takes longer than expected to relax after contraction, it may indicate a condition called myotonia.

Myotonia can affect everyday activities such as opening the hands, walking, climbing stairs, gripping objects and participating in physical exercise. Depending on the underlying condition, it may also occur alongside muscle weakness and problems affecting other body systems.

Understanding myotonia is important for individuals experiencing unexplained muscle stiffness, as well as for healthcare professionals involved in movement assessment, rehabilitation and exercise management.

In this article, we explore what myotonia is, how normal muscle relaxation works, the different types of myotonic disorders, common symptoms, diagnostic investigations and the role of individualised exercise management.

1. What Is Myotonia?

Myotonia is a neuromuscular symptom characterised by delayed relaxation of a muscle after voluntary contraction or mechanical stimulation.

Normally, when you contract a skeletal muscle, it generates force to produce movement. Once the contraction ends, the muscle relaxes, allowing the next movement to occur smoothly.

In myotonia, the muscle may remain contracted longer than expected. This can make certain movements difficult to initiate or complete.

For example, a person may experience difficulty releasing their grip after holding an object. They may also notice stiffness when standing up or beginning to walk after sitting for a while.

Myotonia is not a single disease. It is a feature of several conditions, many of which are genetic and affect the electrical regulation of skeletal muscles.

The severity and pattern of symptoms depend on the specific condition, the muscles involved and whether other body systems are affected.

Key point: Myotonia is not simply ordinary muscle tightness, a muscle tear or post-exercise soreness. Persistent delayed muscle relaxation may require a specific neuromuscular assessment.

2. How Does Normal Muscle Relaxation Work?

To understand myotonia, it helps to understand how skeletal muscles contract and relax.

The process involves electrical signals, ion movement and changes in calcium concentration inside muscle cells.

1. Electrical activation: A nerve signal stimulates the muscle fibre, initiating an electrical impulse.
2. Calcium release: The electrical impulse triggers calcium release inside the muscle cell.
3. Muscle contraction: Calcium allows the proteins responsible for contraction to interact, generating force.
4. Relaxation: Calcium is transported back into storage, and the contractile proteins stop interacting, allowing the muscle to relax.

Ion channels help regulate the electrical behaviour of muscle fibres. In many myotonic conditions, genetic changes affect these channels or other mechanisms that regulate muscle excitability.

As a result, muscle fibres may continue producing electrical activity after the intended contraction, delaying relaxation.

The precise mechanism differs between myotonic disorders. For example, myotonia congenita commonly involves chloride-channel dysfunction, while several sodium-channel myotonias involve changes in sodium-channel function. Myotonic dystrophy has a different underlying genetic mechanism that disrupts normal RNA processing and affects multiple tissues.

3. What Are the Different Types of Myotonia?

Myotonic disorders are commonly grouped into two broad categories: dystrophic myotonia and non-dystrophic myotonia.

Although both can cause delayed muscle relaxation, they differ in their underlying mechanisms, symptoms and associated health concerns.

A. Dystrophic Myotonia

Dystrophic myotonia occurs in a group of genetic conditions known as myotonic dystrophies. These conditions can cause myotonia alongside progressive muscle weakness and wasting, as well as problems affecting other body systems.

Myotonic dystrophy type 1 (DM1)

DM1 is associated with a genetic alteration involving the DMPK gene. Symptoms may affect the hands, lower legs, face and other muscle groups.

Depending on the individual, additional features may include cataracts, cardiac conduction abnormalities, respiratory problems, sleep-related breathing difficulties and metabolic disturbances.

Myotonic dystrophy type 2 (DM2)

DM2 is associated with alterations involving the CNBP gene. It commonly causes muscle stiffness, muscle pain and weakness, often involving muscles closer to the trunk, including the hips and shoulders.

The presentation and severity can vary considerably between individuals.

Myotonic dystrophy requires broader medical attention because its effects are not limited to skeletal muscle. Cardiac, respiratory, eye and other health concerns may need monitoring.

B. Non-Dystrophic Myotonia

Non-dystrophic myotonias are genetic muscle conditions characterised by delayed relaxation without the characteristic multisystem pattern of myotonic dystrophy.

Myotonia congenita

This condition is commonly associated with changes in the CLCN1 gene, which affects chloride channels in skeletal muscle.

Symptoms often begin in childhood, although presentation can vary. Some individuals experience the warm-up phenomenon, in which stiffness temporarily decreases after repeated contractions.

Paramyotonia congenita

Paramyotonia congenita is associated with changes in the SCN4A gene, which affects sodium channels in skeletal muscle.

Stiffness may be triggered or worsened by cold exposure and repeated muscle activity. Unlike the typical warm-up response seen in myotonia congenita, repeated activity may make symptoms worse.

Sodium-channel myotonia

This group of conditions is also associated with altered sodium-channel function. Symptoms can include stiffness in different muscle groups and may vary with activity, temperature and other individual triggers.

Other neuromuscular disorders can produce overlapping symptoms, so a clinical assessment is important to establish the underlying cause.

Why does classification matter?

The type of myotonia influences the expected symptoms, associated health risks and management approach.

A movement or exercise strategy that is suitable for one individual may not be appropriate for another. Identifying the specific condition helps guide treatment and safe physical activity.

4. What Are the Symptoms of Myotonia?

The defining symptom of myotonia is delayed relaxation following muscle contraction. However, symptoms differ depending on the underlying condition.

1. Delayed muscle relaxation

A person may find it difficult to release a grip after holding an object or open their hand immediately after making a fist.

Stiffness can affect other muscle groups, depending on the disorder.

2. Muscle stiffness after rest

Some individuals experience stiffness when beginning to move after sitting or remaining inactive.

This may interfere with walking, standing, climbing stairs or initiating everyday movements.

3. The warm-up phenomenon

The warm-up phenomenon refers to temporary improvement in stiffness after repeated contractions.

For example, someone with myotonia congenita may find that their first few steps feel stiff but subsequent steps become easier.

This response is not present in every myotonic disorder. In paramyotonia congenita, repeated activity can worsen symptoms instead.

4. Muscle pain, cramps and fatigue

Some individuals experience muscle discomfort, cramps or fatigue. These symptoms may influence exercise tolerance and daily function.

Their severity varies between individuals and across different myotonic conditions.

5. Muscle weakness

Muscle weakness may accompany myotonia, particularly in myotonic dystrophy.

Depending on the condition, weakness may affect the hands, ankles, hips, shoulders or other muscle groups.

It is important to distinguish difficulty moving because of stiffness from reduced force-generating capacity due to weakness.

6. Changes in muscle appearance

Some individuals with myotonia congenita have visibly enlarged muscles, a feature known as muscle hypertrophy.

In other conditions, muscle wasting or reduced muscle mass may occur.

Muscle appearance alone cannot establish a diagnosis.

Symptoms beyond the muscles

In myotonic dystrophy, symptoms may involve other body systems.

• Eyes: Cataracts or other visual problems.
• Heart: Abnormalities in electrical conduction or heart rhythm.
• Respiratory system: Respiratory muscle weakness or sleep-related breathing problems.
• Digestive system: Constipation, reflux, swallowing difficulties or other gastrointestinal symptoms.
• Metabolic health: Insulin resistance and related abnormalities.

These features are not present in every person with myotonia. They are particularly important when evaluating myotonic dystrophy, which can affect multiple body systems.

5. What Causes Myotonia?

Myotonia is commonly associated with genetic changes that interfere with the normal regulation of skeletal muscle activity.

Genes provide instructions for producing proteins involved in muscle function. Some of these proteins form ion channels, which control the movement of electrically charged particles across cell membranes.

When an alteration affects these processes, muscle fibres may become excessively excitable, resulting in repeated electrical activity and delayed relaxation.

The underlying genetic mechanism differs between conditions.

These associations help clinicians select appropriate investigations, but the table is not a substitute for genetic testing or clinical interpretation.

Is myotonia inherited?

Many myotonic disorders are inherited, but their inheritance patterns differ.

Some conditions can be passed from an affected parent to a child, while others require disease-associated variants from both parents. Occasionally, a genetic alteration arises spontaneously.

A family history can therefore be useful during assessment, but the absence of affected relatives does not rule out a genetic myotonic disorder.

Genetic counselling may help individuals and families understand inheritance patterns and the implications of genetic testing.

6. How Is Myotonia Diagnosed?

Diagnosis requires a clinical assessment and, where indicated, appropriate investigations.

Because several conditions can cause muscle stiffness, the aim is to determine whether the symptoms are consistent with myotonia and identify the underlying disorder.

1. Clinical history and physical examination

The healthcare professional may ask:

• When did the symptoms first appear?
• Which muscles are affected?
• Does stiffness improve or worsen with repeated movement?
• Does cold exposure influence symptoms?
• Is muscle weakness or fatigue present?
• Have family members experienced similar symptoms?

The examination may include observing how muscles contract and relax during specific movements.

2. Creatine kinase blood test

Creatine kinase (CK) is an enzyme found in muscle tissue. Its concentration in the blood may rise when muscle cells are affected.

Some individuals with myotonic conditions have elevated CK levels. However, levels vary, and a normal or elevated result cannot independently confirm or exclude myotonia.

3. Electromyography (EMG)

Electromyography evaluates the electrical activity of muscles.

Needle EMG can identify characteristic repeated electrical discharges associated with myotonia. This can help distinguish myotonic disorders from other neuromuscular conditions.

4. Genetic testing

Genetic testing examines DNA for alterations associated with specific disorders.

Depending on the suspected condition, it may help confirm the genetic cause and distinguish between different forms of myotonia. The appropriate test depends on the clinical presentation and suspected genetic mechanism.

5. Additional investigations

Further investigations may be appropriate depending on the symptoms and suspected diagnosis.

These can include:

• Blood electrolyte measurements when an electrolyte-related muscle disorder is suspected.
• Short exercise tests in selected cases.
• Cardiac investigations when myotonic dystrophy or a related cardiac problem is suspected.
• Respiratory function or sleep assessments when breathing-related symptoms are present.

Not every person requires every investigation. The healthcare professional determines the appropriate diagnostic pathway based on the clinical findings.

Important: Muscle stiffness is a symptom, not a diagnosis. Persistent or unexplained stiffness should be assessed by an appropriate healthcare professional.

7. How Is Myotonia Managed?

Management depends on the specific diagnosis, symptom severity, functional limitations and involvement of other body systems.

There is no single treatment plan suitable for every form of myotonia. Management may include medical treatment, physiotherapy, activity modification, individualised exercise and regular monitoring.

1. Medical management

A neurologist or another appropriate specialist may consider medication to reduce myotonic stiffness.

Mexiletine is one medication used to treat symptomatic myotonia in selected patients. Its suitability depends on the individual's condition, medical history and potential adverse effects. Because mexiletine has cardiac effects, medical supervision and appropriate cardiac assessment and monitoring are important.

Medication should not be started, stopped or adjusted without advice from the treating healthcare professional.

2. Physiotherapy and functional management

Physiotherapy can help assess how muscle stiffness, weakness and movement difficulties affect everyday activities.

Depending on the individual's needs, a programme may address:

• Functional movement difficulties.
• Walking, balance and coordination.
• Strength and physical conditioning.
• Mobility and movement control.
• Fatigue management.
• Adaptations for daily tasks.
• Safe participation in appropriate physical activities.

Physiotherapy does not correct the underlying genetic alteration. Its role is to address relevant functional limitations and support physical activity where appropriate.

The programme should be individualised and coordinated with the healthcare team when necessary.

3. Individualised exercise

Exercise may form part of management, but it should be selected carefully.

Some individuals with myotonia congenita experience temporary improvement in stiffness after repeated muscle contractions. Others, particularly those with paramyotonia congenita, may experience worsening stiffness with repeated activity or cold exposure.

Exercise recommendations should reflect the specific diagnosis, symptoms, physical capacity and medical advice. Evidence that exercise can improve general fitness does not mean it eliminates myotonia itself.

4. Identifying and managing triggers

Some individuals find that specific circumstances influence their symptoms. Depending on the condition, these may include cold exposure, particular movements or certain patterns of physical activity.

Recognising individual triggers can help the person and their healthcare team adapt daily activities and exercise accordingly.

5. Monitoring associated health problems

People with myotonic dystrophy may require monitoring beyond their musculoskeletal symptoms.

Depending on the condition, this may include assessment of cardiac function, respiratory health, vision, metabolic health and other affected systems.

Managing muscle stiffness alone may not address the full range of health concerns associated with dystrophic myotonia.

8. Myotonia and Exercise: What Should Athletes and Fitness Professionals Know?

Myotonia is particularly relevant to sports science and physiotherapy because muscle relaxation, movement coordination and physical performance are closely related.

However, muscle stiffness should not automatically be interpreted as poor flexibility, insufficient warm-up or a lack of strength.

In a myotonic disorder, the underlying issue involves abnormal regulation of muscle electrical activity.

Understanding the warm-up phenomenon

Some individuals with myotonia congenita experience reduced stiffness after repeated contractions. This may influence how they perform activities such as walking, climbing stairs or initiating movement after rest.

However, the response differs between myotonic conditions. In paramyotonia congenita, repeated activity may worsen stiffness.

A conventional warm-up routine should therefore not be assumed to resolve symptoms in every person with myotonia.

Strength and conditioning considerations

Before participating in a structured strength and conditioning programme, an individual with diagnosed or suspected myotonia may need appropriate medical assessment.

Relevant considerations include:

• Whether the condition is dystrophic or non-dystrophic.
• Whether muscle weakness accompanies stiffness.
• Whether exercise or cold exposure aggravates symptoms.
• Whether cardiac or respiratory involvement is present.
• Whether symptoms affect balance or functional movement.
• Whether the individual experiences unusual fatigue or difficulty recovering.

Exercise professionals should work within their scope of practice and coordinate with the treating healthcare team when appropriate.

The objective is to support suitable physical activity while recognising the individual's clinical needs—not to prescribe a generic programme based solely on visible stiffness.

A practical example

The following is a hypothetical example for educational purposes, not a real patient case.

Consider a recreational badminton player who experiences stiffness in the hands after gripping a racket following a period of rest. The first few gripping movements feel more difficult than subsequent movements.

Rather than immediately assuming the problem is caused by poor grip strength or inadequate stretching, the player seeks a clinical assessment.

The healthcare professional reviews the symptom pattern, medical history and other relevant findings. If myotonia is suspected, appropriate investigations may be recommended.

If a myotonic disorder is confirmed, the player's exercise and sports participation plan can be considered in light of the specific diagnosis, symptom response and any associated health concerns.

Key lesson: Movement assessment can identify a functional difficulty, but it cannot independently establish the medical cause.

9. Common Myths About Myotonia

Myth 1: Myotonia is the same as ordinary muscle tightness.

Fact: Ordinary muscle tightness can have many causes. Myotonia specifically refers to delayed muscle relaxation following contraction and may be associated with genetic neuromuscular conditions.

Myth 2: Everyone with myotonia experiences the same symptoms.

Fact: Symptoms vary by condition and individual. Some people mainly experience stiffness, while others may also have muscle weakness, pain or problems affecting other body systems.

Myth 3: Repeated movement always improves myotonia.

Fact: Repeated contractions may temporarily reduce stiffness in myotonia congenita. In some other conditions, repeated activity may worsen stiffness.

Myth 4: Myotonia is always associated with progressive muscle wasting.

Fact: Progressive weakness and wasting are characteristic features of myotonic dystrophy, but they are not defining features of non-dystrophic myotonia.

Myth 5: Stretching alone can treat myotonia.

Fact: Myotonia involves abnormal regulation of muscle electrical activity. Stretching alone does not correct the underlying genetic mechanism. Management should be guided by the diagnosis and individual needs.

Myth 6: Everyone with myotonia should avoid exercise.

Fact: Exercise may be appropriate for many individuals, but the type, intensity and progression should reflect the condition, symptoms and associated health concerns. Medical and physiotherapy guidance may be necessary.

Myth 7: A single test can always diagnose myotonia.

Fact: Diagnosis may require a combination of clinical assessment, family history, EMG, genetic testing and other investigations, depending on the suspected condition.

10. Why Individualised Assessment Matters

Two individuals with muscle stiffness may have very different underlying conditions.

One person may experience temporary stiffness that improves with repeated contractions. Another may experience progressive muscle weakness alongside stiffness, while a third may have symptoms involving other body systems.

For this reason, assessment should consider more than visible movement restriction.

• Symptom history: When stiffness occurs and how it changes with activity.
• Functional movement: How symptoms affect walking, gripping, stair climbing and everyday tasks.
• Muscle strength: Whether weakness accompanies stiffness.
• Movement control: Whether symptoms interfere with coordination or balance.
• Exercise tolerance: How the individual responds to physical activity.
• Medical history: Whether a diagnosed or suspected neuromuscular condition requires additional precautions.
• Associated health concerns: Whether other body systems need medical evaluation.

A movement assessment can help identify functional limitations and inform appropriate exercise planning. However, it cannot replace neurological assessment, EMG or genetic testing when these investigations are clinically indicated.

Persistent, worsening or unexplained muscle stiffness should be discussed with a qualified healthcare professional.

Frequently Asked Questions About Myotonia

1. Is myotonia a disease or a symptom?

Myotonia describes delayed muscle relaxation. It is a characteristic feature of several conditions, including myotonia congenita and myotonic dystrophy.

2. What is the main symptom of myotonia?

The main symptom is difficulty relaxing a muscle immediately after it contracts. For example, a person may struggle to release a grip or experience stiffness when beginning to move.

3. What causes myotonia?

Myotonia is commonly associated with genetic alterations affecting proteins involved in muscle electrical activity. The specific cause depends on the underlying condition.

4. Can myotonia affect physical performance?

Yes. Muscle stiffness, weakness, pain or fatigue may influence movement, exercise tolerance and participation in sports. The effect depends on the specific condition and the individual's symptoms.

5. Can exercise help people with myotonia?

Exercise may support physical conditioning and functional ability in appropriately selected individuals. However, its effect on stiffness varies by condition. An individualised programme should account for symptoms, physical capacity and relevant medical precautions.

6. Is myotonia the same as myotonic dystrophy?

No. Myotonia is delayed muscle relaxation, whereas myotonic dystrophy is a genetic disorder that causes myotonia and may also cause progressive muscle weakness, wasting and problems involving other body systems.

7. Which tests are used to diagnose myotonia?

Assessment may involve a clinical examination, family history, creatine kinase testing, EMG and genetic testing. Other investigations may be used when a specific condition or associated complication is suspected.

8. Should someone with myotonia consult a physiotherapist?

A physiotherapist may help assess functional difficulties, mobility, strength and exercise tolerance. However, suspected myotonia requires appropriate medical assessment, and physiotherapy should form part of a broader management plan when indicated.

Key Takeaways

• Myotonia is delayed muscle relaxation following contraction.
• It is commonly associated with genetic changes affecting the regulation of skeletal muscle activity.
• Myotonic disorders are broadly classified as dystrophic or non-dystrophic.
• Symptoms may include stiffness, difficulty releasing a grip, muscle pain, fatigue and, in some conditions, weakness.
• The warm-up phenomenon occurs in certain forms of myotonia, but repeated movement does not improve symptoms in every condition.
• Diagnosis may require clinical assessment, EMG and genetic testing.
• Medical management, physiotherapy and individualised exercise may form part of care.
• People with myotonic dystrophy may require monitoring for complications affecting other body systems.
• Persistent or unexplained muscle stiffness warrants appropriate professional assessment.

The Sports2Science Perspective

At Sports2Science, understanding movement begins with understanding the individual.

Muscle stiffness can influence movement quality, exercise participation and physical performance. However, the same movement observation may have different explanations in different individuals.

In conditions such as myotonia, distinguishing a functional limitation from a possible underlying medical disorder is particularly important.

Sports2Science offers services relevant to movement and physical performance, including sports physiotherapy, functional movement assessment, strength and conditioning, biomechanical assessment and sports performance assessment.

Where appropriate, these services can help identify functional limitations, understand movement requirements and inform individualised exercise planning.

For someone with suspected myotonia, medical evaluation is the priority. If a diagnosis has been established and exercise participation is appropriate, movement and physical performance assessments may complement the person's broader healthcare plan.

Assessment should guide the next step, not replace medical diagnosis.

Final Thought

Muscle stiffness is not always a simple problem of flexibility, strength or warm-up.

When a muscle takes longer than expected to relax after contraction, the underlying mechanism may be different from ordinary muscle tightness.

Understanding that distinction helps individuals seek appropriate assessment and enables healthcare and exercise professionals to make more informed decisions about movement and physical activity.

Better movement starts with understanding what is happening beneath the surface.

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Scientific References

1. GeneReviews — Myotonia Congenita. National Center for Biotechnology Information.
   https://www.ncbi.nlm.nih.gov/books/NBK1355/
2. Consensus-Based Care Recommendations for Adults with Myotonic Dystrophy Type 1. Neurology: Clinical Practice.
   https://pmc.ncbi.nlm.nih.gov/articles/PMC6294540/
3. Clinical Guide for the Diagnosis and Follow-up of Myotonic Dystrophy Type 1.
   https://pubmed.ncbi.nlm.nih.gov/30685181/
4. Consensus-Based Care Recommendations for Pulmonologists Treating Adults with Myotonic Dystrophy Type 1. Respiration. 2020;99(4):360–368.
   https://pubmed.ncbi.nlm.nih.gov/32299079/
5. Clinical Care Recommendations for Adults with Myotonic Dystrophy Type 1. Myotonic Dystrophy Foundation.
   https://myotonic.org/resources/clinical-care-recommendations-for-adults-with-dm1/
6. Cleveland Clinic — Myotonia: Causes, Symptoms and Treatment.
   https://my.clevelandclinic.org/health/diseases/22334-myotonia