Shoulder pain can stem from one or more of the following causes: 1  Strains from overexertion. 2  Tendonitis from overuse. 3  Shoulder joint instability. 4  Dislocation. Collar or upper arm bone fractures.  Frozen 1  shoulder. Pinched nerves (also called radiculopathy)
Joint pain can affect one or more joints. Joint pain can be caused by many types of injuries or conditions. It may be linked to arthritis, bursitis, and muscle pain. No matter what causes it, joint pain can be very bothersome. Some things that can cause joint pain are: Autoimmune diseases such as rheumatoid arthritis and lupus.
Most people believe that lactic acid causes muscle soreness because that was the findings of scientists many years ago. Lactic acid is the culprit for immediate muscle soreness. When you are lifting weights, for example, the muscle you are working will burn, and it will eventually feel fatigued.