After a couple of months — the way Stone understood it — the various functions of the body adapted to microgravity, settling down to a new equilibrium, different from that on Earth. The neurovestibular system, the balance mechanism within the ear, was the first to fall apart — hence, space sickness — but also the first to recover, after a few days. The body’s fluid balance would adjust then, and next the cardiovascular system, the heart and blood vessels.

But things didn’t go back to Earth-normal.

Stone’s brain, which didn’t know about microgravity, thought that all that extra blood was pooling in his head because there was too much fluid in his body, and it told his kidneys to release more urine. And that way lay dehydration. So Stone had to drink an extra five pints of fluid a day, laced with water-salt imbalance counteragents. That was something NASA had learned from the Russians.

But all the extra pissing flushed the calcium and potassium out of his bones. The calcium deficit could make his bones brittle, or give him kidney stones, and the potassium could leave him prone to heart problems; so he had to take dietary supplements, and there were anabolic steroids in case any of them suffered severe bone loss.

His muscles didn’t do any work they didn’t have to, and — if he left them alone — they would atrophy. So he had to go through all the exercise on the isokinetic device. There were other measures, too, like the penguin suit — so-called because it made you waddle around on the ground during training — a set of elastic straps that tried to pull you into a fetal position all the time, so your muscles were constantly working, as if against gravity. And there was the chibis, a Russian word for lapwing bird, another idea borrowed from the Soviets: reinforced leggings that reduced the air pressure over the legs, to make the heart work harder to pull blood up from the lower body.

The isokinetic exercises ought to help with reducing bone mineral loss, too; bones always kept themselves just strong enough to resist the maximum loads imposed by the muscles.

The crew had to submit, every two or three days, to electrocardiograms, seismocardiograms, measurements of their breathing rates and volume. All of it was fed back to the surgeons on Earth. All the biomed stuff added up to a whole day lost out of every week.

None of it was popular. Stone realized, though, that it was up to him to set an example to the others. If he skimped, so would they. So he made sure he did at least his regulation hour’s exercise, every day.