I still remember the skin on my grandmother’s arms. It had that crumpled-silk feeling that I used to love running my cheeks over. I did not know then that it was called sarcopenia or muscle wasting, often seen in the very elderly or children with progeria, as was Auro in the film Paa. Muscle is what gives us our youthful limbs, the full cheeks and the expressive faces. Making up nearly 30% of our body mass, skeletal muscle or voluntary muscle enables us to walk, run, lift, blink, smile and breathe. Among the largest cells in the body, skeletal muscle cells connect to the bones through tendons. Each muscle is a bundle of muscle cells stretched from tendon to tendon, contracting in sync. Each muscle cell is packed with micro-bundles of proteins known as actin and myosin that slide against each other like in the boom of a telescopic crane. This sliding results in the contraction or expansion of the muscle, forcing the leg to bend, the lips to curve or the chest to expand. I...