Biceps Intermuscular Septum Syndrome (Fascial Restriction Between the Two Heads of the Biceps). A hidden cause of pulling pain in the arm and shoulder stiffness

What Is the Biceps Muscle?

The biceps muscle is a large muscle at the front of the upper arm. It has two parts (heads):

• Long head – attaches inside the shoulder joint

• Short head – attaches to the front of the shoulder blade

Both heads join together near the elbow and attach to the forearm bone, with an additional connective tissue sheet that helps stabilise the tendon.

Together, the two heads:

• Bend the shoulder

• Bend the elbow

• Rotate the forearm outward (palm up)

Because the two heads start in different places, they also support different shoulder movements:

• The long head helps lift and rotate the arm outward

• The short head helps bring the arm inward

  
  

What Goes Wrong in This Condition?

Between the two heads of the biceps there is a thin layer of fascia (connective tissue) that should allow them to slide smoothly against each other.

In some situations, this fascia becomes thickened or stiff (a process called densification).When this happens:

• The two parts of the biceps cannot glide properly

• Movement becomes restricted

• Pain appears, especially during stretching

  
  

Common Causes

The most common causes include:

1. Sedentary Lifestyle

When the arm is not used through its full range of motion, the fascia adapts by becoming stiffer. Over time, this reduces mobility and causes pain during stretching.

2. Strength Training Errors

This problem is common in people who train biceps only in one movement pattern (for example, curls in a single plane).

The body adapts to what it does most often. If movement is repetitive and limited:

• Fascia adapts to that direction only

• Movement in other directions becomes restricted

3. Compensation Patterns in the Body

The biceps is highly sensitive to global compensation patterns in the body.

Past injuries, overload, postural problems, or even internal issues can cause the biceps to:

• Become too tight

• Or too weak

In both cases, the body may stiffen the fascia around the muscle to “protect” movement—leading to pain.

Symptoms – How It Usually Feels

The key symptom is:

• A pulling or stretching pain along the biceps

Important characteristics:

• Pain appears only when the muscle is stretched

• No pain at rest

• Pain limits end-range movements

You may notice difficulty with:

• Fully extending the arm behind the body

• Horizontal extension of the shoulder

• Fully straightening the elbow in certain arm positions

  
  

Diagnosis

Diagnosis is usually based on:

• A very characteristic pulling pain

• Clear movement limitations

• Pain only during stretching, not contraction

Before starting treatment, it is important to rule out other causes such as:

• Neck problems

• Thoracic outlet issues

• Shoulder joint pathology

Once these are excluded, the diagnosis is usually straightforward.

Treatment – What Actually Helps

This condition responds very well to fascial-oriented physiotherapy.

There are several effective fascial therapy approaches, and the physiotherapist chooses the most appropriate one based on experience and assessment.

Treatment focuses on:

• Restoring glide between the two heads of the biceps

• Improving tissue elasticity

• Reintroducing full, multi-directional movement

⚠️ Important:Treatment will not provide lasting results unless:

• Daily habits are changed

• Training errors are corrected

• The original cause of the problem is addressed

  
  

When to See a Physiotherapist

You should consider physiotherapy if you have:

• Biceps pain only when stretching

• Arm stiffness without clear injury

• Shoulder or elbow motion limited by a pulling sensation

• Pain that does not improve with rest or massage

Early treatment prevents long-term movement restriction.

Why This Problem Is Often Missed

This condition:

• Does not show on imaging

• Does not cause sharp pain

• Is often mistaken for muscle tightness or shoulder issues

A detailed movement assessment is key.