The muscle cells require cell division to produce sufficient numbers of daughter cells to add nuclei to growing muscle fibers. The size of the muscle fiber depends on the amount of nuclei. Without weight-bearing, cell division slows down. Therefore, not as many nuclei are predicted to be made, and this may adversely affect the individual in later life. Later, as the "PERSON" matures and their muscles attempt to grow to full size, by not having enough nuclei, the muscle fibers themselves may be stunted. We may find that some of their muscle fibers are actually smaller than normal and unless they become athletes, you wouldn't really notice that they are not as strong as someone else. They may be strong enough to do normal recreational activities, but not to really push the system, since they have a deficit of permanently smaller muscle fibers.

As we age, some of the muscle cells that were produced during the cell division stay around so that when there's the natural loss, they repair the deficit. There's also a replenishment necessary when we injure a muscle, which happens very frequently with sports. Any time your muscle is sore, you have caused damage followed by regeneration or repair. Repair depends on some of the muscle cells made early on to proliferate and add to and repair the muscle fiber. So an individual who's in their 60's or 70's normally uses up many of these cells. Individuals with fewer cells to start with may, in a sense, age faster, and they wouldn't be able to repair themselves as well. These are possible things to look for in humans if we find an effect on the rat. We are allowing some of the animals returning from space to grow up as young adults in Earth's gravity. And then we will look at their muscle fibers, cells and nuclei, and determine if there was any stunting or any other deficiencies.

The next step would be to ask how much stimulation is necessary for normal development. In other words we would take developing rats on Space Station in the future where there will be a centrifuge to create artificial gravity. We can put them at one-gravity comparable to Earth, maybe 1 hour a day. Maybe that will be enough to stimulate normal development. For this countermeasure of replacing gravity, "MAYBE" 1/2 gravity would work. We will be looking for the chemical signal that causes muscle cells to multiply, and how often do you have to give this signal. If we found that three hours a day worked, then we could use that information to go back to the premature infants in the incubator. These little guys would be encouraged to push against something for three hours a day - do a little exercise.

It's that kind of issue. Then you ask where do you go from there? We would look further for trying to figure out the mechanism down at the molecular and gene control level.