As growth hormone levels decline, muscle mass and bone strength decrease; ligaments and tendons weaken, and cartilage, skin, hair, and nails become thin. As collagen throughout the body loses its elasticity, the skin sags and wrinkles, joints become stiff and painful, and arteries harden and thicken. These muscle, collagen, and bone tissues have growth hormone receptors, but there is little growth hormone to “activate” growth and repair in these tissues.