Glucosamine and chondroitin are components – or building blocks – of normal cartilage. Glucosamine is a substance found naturally in the fluid that surrounds your joints, while chondroitin is found in the cartilage around your joints – both substances play a role in keeping your joints cushioned and lubricated. A combination of these glycosaminoglycans are often supplemented by runners who develop issues in their joints due to the ongoing impact and frequency of training.