Any movement that stresses your joints can result in popping and cracking sounds. Lifting weights often causes the shoulder joints to make these noises. There is no definitive answer as to why this happens, according to Johns Hopkins Medicine's Orthopaedic Surgery unit, though two theories have been proposed.
The buildup and release of gases in the synovial fluid around your joints is suspected to cause popping. The slip of tendons across joints has also been suggested as the cause of cracking sounds. Joint-cracking without pain is not typically indicative of a medical problem.
Popping and cracking sounds in your joints can be disconcerting not to mention startling. If there's no undue pain accompanying the symphony of sounds, then there's usually nothing to worry about.
Gases That Cause Cracking Sounds
Synovial fluid — the substance that lubricates your joints — is composed of oxygen, carbon dioxide and nitrogen. These gases can bubble out of the synovial fluid when negative pressure is applied to a joint, such as when you lift weights.
A pop or crack can result from the escape of these gases as demonstrated in X-rays, according to the scientific facts pages of the Library of Congress. Once the gases are reabsorbed into the synovial fluid, they can again be expelled, creating more cracking sounds.
Action of the Joints
The action of the joints used in lifting weights might contribute to the cracking sounds you hear. Tendons or ligaments might be slipping in and out of place as you move your shoulders, similar to the twang of a rubber band bowstring.
Eroded bone and stressed supportive joint tissues can increase the likelihood of cracking sounds while moving your shoulders beyond their normal range of motion, such as over your head, while you raise heavy weights.
Read more: How to Improve Joint Strength
Other Contributing Factors
Age is a contributing factor to more cracking and popping sounds, says Cleveland Clinic. Your cartilage has been wearing away for years, the surfaces get rough, and hey presto, you hear more cracking noises.
If you have osteoarthritis — which often results in worn-down or roughened joint and cartilage surfaces — you might experience more cracking while lifting weights than people without this underlying condition.
If the cracking noises are accompanied by pain, a decrease of flexibility or weakness in the affected joint, you might be experiencing a joint problem. Consult your doctor if any of these symptoms occur.
What Does It All Mean?
Joint-cracking is usually harmless, and, contrary to popular belief, has never been proven to cause or exacerbate arthritis in that joint, although it may lead to minor swelling in the hands and a weakening of your grip.
If you don't feel pain during the cracking sounds resulting from lifting weights, you probably have nothing to worry about. A gentle stretch of the joint that's cracking or snapping during weightlifting could make the sound diminish or disappear.