Muscles: National Geographic investigates the science of muscle by taking a journey inside the bodies of two remarkable humans with startling muscular disorders. 31-year old Jason Dunn lives with Dystonia, a rare disease that causes his brain to send faulty messages to his muscular system. Every waking moment his muscles flex out of his control, twisting his body into unusual positions. Ami Ankileweitz has Spinal Muscle Atrophy, a genetic disorder that has caused his muscles to wither away. Skin: National Geographic explores the science of skin by taking US inside the bodies of two extraordinary humans living with puzzling genetic conditions. 14-year old Hunter Steinitz suffers from Harlequin Ichthyosis, a rare condition that causes her skin to grow layer upon layer without flaking off, progressively encasing her in a tight suit of thick skin. As for Garrett, he has no skin to spare. His skin lacks the Velcro it needs to adhere to the body, leaving parts of it completely raw and exposed. Using leading-edge animation, travel below the surface and into the extraordinary bodies of Hunter and Garrett to discover what makes and breaks this intricate and delicate tissue we call skin.