Key substances in Acti-Flex 4000 work together to improve performance by increasing the horse's supply of joint-lubricating synovial fluid, which repairs and strengthens body parts that running puts under high stress. Glucosamine Sulfate, Chondroitin Sulfate, Methylsulfonylmethane (MSM), and Superoxide Dismutase occur naturally in the body, serving the function of repairing joints and many other tissues.