Tough tissue is a type of connective tissue found in the body that provides strength and support. GRISTLE, SINEW, and TENDON are all examples of tough tissue. GRISTLE is a type of tough tissue found in joints and cartilage, and is composed of collagen fibers. SINEW is a type of tough tissue found in muscles and tendons, and is composed of both collagen and elastin fibers. TENDON is a type of tough tissue that connects muscle to bone, and is composed of collagen fibers.