Understanding Your Shoulder: Why This Complex Joint Often Causes Pain

Ever wondered why shoulder pain is so common? The shoulder is one of the most mobile joints in the human body, but with that incredible range of motion comes complexity—and a higher risk of problems.

In this quick guide, we’ll simplify how your shoulder works, explain why it’s prone to pain and injury, and share what you can do to keep it healthy.

Want a deeper dive into the details? See our full Shoulder Anatomy Explained page ➜

How the Shoulder Works

The shoulder is a ball-and-socket joint that allows you to lift, reach, and rotate your arm in almost every direction. It’s made up of three main bones—the humerus (upper arm), scapula (shoulder blade), and clavicle (collarbone).

The three main bones of the shoulder - the Scapula, the Clavicle and the Humerus

Unlike the hip joint, which is deep and stable, the shoulder socket is quite shallow. This gives you amazing mobility but means the shoulder relies heavily on soft tissues for stability:

• Rotator cuff muscles & tendons help keep the joint centred

• Ligaments & joint capsule provide extra support

• Bursa (fluid-filled sacs) reduce friction

When everything works together, your shoulder moves smoothly. But if one part becomes irritated or weak, pain and stiffness can quickly follow.

Why Shoulders Are Prone to Pain

Because the shoulder is so mobile, it’s more vulnerable to strain, overuse, and injury. Some of the most common causes include:

• Repetitive movements (sports, gym, or work tasks)

• Poor posture, which changes the way the joint moves

• Sudden trauma, like a fall or awkward lifting

• Natural age-related changes in tendons

• Hormone-related changes in tendons

When these factors combine, they can lead to rotator cuff tendinopathy, impingement, frozen shoulder, or even joint instability.

Common Shoulder Injuries

• Rotator cuff tendinopathy – wear and irritation of the tendons

• Shoulder impingement – when tendons get trapped and compressed during movement

• Frozen shoulder (adhesive capsulitis) – stiffness and pain that limits mobility

• Shoulder instability – looseness or dislocation, often after an injury

• Rotator cuff tear – Traumatic or degenerative tearing of the muscles

Each of these conditions affects the shoulder differently, but most respond well to a combination of targeted physiotherapy, strengthening, and manual treatment. In some cases you may be referred for specialist investigations such as an Ultrasound Scan or MRI scan, or even a consultant surgeon.

Quick FAQs

Why is shoulder pain so common?

Because the shoulder sacrifices stability for mobility, it relies on soft tissues for support. Overuse, poor posture, or trauma can easily irritate tendons and joints.

How can I protect my shoulders?

Strengthening your rotator cuff muscles, maintaining good posture, and avoiding repetitive strain can significantly reduce your risk of injury.

When should I see a physiotherapist?If your shoulder pain lasts more than a couple of weeks, limits your movement, or affects your sleep, it’s worth getting assessed by a professional.

Need Help With Shoulder Pain?

Shoulder pain doesn’t have to hold you back.

If you’re struggling with discomfort, stiffness, or weakness, we can help. Longer appointments, clear diagnosis, and evidence-based treatment mean you’ll get the right plan for your recovery.

Learn more about shoulder anatomy and why it matters ➜

Book an appointment with Chris Heywood Physio ➜