Joint movement is controlled by opposing sets of muscles. When the joint is not flexed the muscle is supposed to relax completely by reflex action. If it does not the muscles work against each other and grind the joint surfaces together harder than normal and aggravate the wear and tear of the joint surfaces, aggravating arthritic conditions. At the same time the pressure in the synovial fluid is greatly increased and bursitis can result. Chronic "bracing" is when all muscles stay contracted to a certain extent, even when asleep.