It can be difficult or even impossible to tell the difference between a muscle strain and tendonitis.

Muscles and tendons are closely related. A tendon is a specialized part of a muscle that attaches the muscle to bone. When a muscle contracts, the tendon pulls on the bone, allowing the bone to move.

It can be impossible to determine which structure is causing pain because tendons and muscles are physically close to one another and subject to similar stresses. In addition, muscle strain and tendonitis may occur at the same time.

In some locations, it's easy to tell the difference between a muscle strain and tendonitis. For example, the Achilles tendon travels near the surface of the skin and attaches the calf muscles to the back of your heel. Your doctor can examine you and see whether the pain, swelling, warmth or injury is confined to the tendon or in the calf muscles above. In general, pain near a joint is more likely to be related to tendonitis than to a muscle strain.

Treating a muscle strain and tendonitis is similar so it's rarely essential to distinguish between the two. Rest, pain relievers, anti-inflammatory medicines and applying cold packs for 24 to 48 hours after an injury usually work well for both problems.