Shoulder pain is notoriously tricky. It’s common for people to lump every ache into “tendonitis” or “frozen shoulder,” but these two issues are actually worlds apart. While a quick look might make them seem similar, the way we treat them is completely different. If your clinician isn’t looking closely, they might miss the subtle signs that tell these two apart.

Rotator Cuff Tendonitis (The “Overload” Issue)

Think of this as an irritation problem. Your tendons—the thick tissues connecting muscle to bone—have been pushed a bit too far and are now inflamed or overloaded.

  • How it feels: You can still move your arm through its full range, but it hurts to do so. You might feel a sharp pinch when reaching for a seatbelt or lifting a grocery bag.
  • The “Painful Arc”: Usually, the pain kicks in at a specific point—like when your arm is halfway up—but eases off once you get past that spot.
  • Strength: Your muscles are technically capable of lifting weight, but the pain makes you feel weak.

Frozen Shoulder (The “Stiffness” Issue)

Clinically known as adhesive capsulitis, this is a problem with the “sleeve” of the joint (the capsule) tightening up. It’s not just about pain; it’s about a literal physical blockage.

  • How it feels: Your shoulder feels “stuck.” If someone else tried to move your arm for you, it wouldn’t go any further than you can move it yourself.
  • The Rotation Test: The biggest giveaway is losing “external rotation”—that movement of rotating your forearm outward away from your body.
  • The Progression: It often starts with intense, nagging pain (the “freezing” phase) and gradually transitions into a stage where the pain dulls but the shoulder becomes incredibly stiff.

Why the distinction is a big deal

Treating a frozen shoulder like tendonitis (or vice versa) is a recipe for frustration.

  • For Tendonitis: We want to strengthen. The goal is to gradually add weight and “re-teach” the tendon how to handle stress.
  • For Frozen Shoulder: Pushing too hard with heavy weights too early can actually make the inflammation worse. Here, the focus is on staged mobility and staying patient while the joint capsule slowly thaws out.

If you’ve been doing “rehab” for weeks and aren’t seeing progress, it might not be the exercises—it might be the diagnosis.