Research appearing in the Journal of Strength and Conditioning Research (2007 Aug;21(3):661-7) looked at the effect protease enzyme supplements had on muscle damage after exercise. The double-blind, placebo-controlled study involved twenty male subjects who were tested for the strength, pain (rated by subjective questionnaire), and indicators of muscle damage (creatine kinase activity and myoglobin concentration). They were given either an enzyme supplement or a placebo. It was found that supplementation reduced strength loss immediately after exercise.
In Clinical Experimental Rheumatology (Jan-Feb;24(1):25-30) compared enzyme supplementation to NSAID use in patients with osteoarthritis of the hip. The double-blind, placebo controlled study lasted six weeks and involved 90 subjects and found that enzyme to be comparable to the drug in relieving pain, joint stiffness and improving function.