16
The tall, skinny Martian physique works fine on Mars, but a lot less well on Earth. What makes the difference is gravity. The Martian who comes to Earth suddenly discovers that he has an extra forty or so kilograms to carry around with him—all the time—and his body's musculature isn't up to it.
So the muscles are built up with polysteroids. That's easy enough. But then the muscles can exert more force than the bones they are attached to can withstand, so to keep the skeleton intact the bones have to be built up with more calcium. That works, too, but more slowly; so while the skeleton is becoming denser and more rigid the long bones of the legs, particularly, need to be scaffolded from outside: thus the leg braces. But then there are other problems. Those new muscles demand more oxygen, so while the bone marrow is making more red corpuscles an extra couple of liters of whole blood are pumped in to tide them over. Then there's the heart itself. It has to work harder in order to move all this extra blood around. A whole array of beta blockers and stimulants are needed to help the heart do its new job.
And then, when all this has been done, the result is a body that has been beefed up, but still remembers its birthplace conditions. It tires. It slows down. What they say is true: It's easy enough to take the boy out of Mars, but you can never, ever, take Mars out of the boy.