Microgravity: the roadblock to Mars?

After Stanley G. Love spent two weeks in space without exercising, he lost 8lbs of muscle mass in his legs alone. If we're set to go to Mars, astronauts would be travelling in microgravity for nine months. Could living without gravity be a major concern for our wouldbe Mars-bound astronauts? Neurosurgeon Mark Wilson thinks a long haul trip to the red planet could have some serious - but not insurmountable - health effects, as he explained to Kat Arney...

Mark - There are many effects. My area of research is what happens to the brain in microgravity and hypoxia. What happens is is that because you haven't got gravity pulling blood into your legs, you get this fluid shift and we think that the intracranial pressure rises. What's happening, we're finding in longer space missions now, the chronic changes that are occurring are actually causing another phenomenon which is known as VIIP or Visual Impairment and Intracranial Pressure in space where the astronauts are losing peripheral vision and this is also a long term problem that could be an issue in a mission such as one to Mars.

Kat - So basically, all their bloods kind of going into their head and the fluid has got to go somewhere.

Mark - Yeah. I think what's happening is that you've got this reduced ability to drain venous blood. If you're sitting here now, you're putting about a litre of blood into your head every minute and that litre of blood has to get to get out every minute as well. When you have not got gravity helping that and you can't drain blood quick enough.

Kat - So, that's what's going at the head-end. So, what about further down, the rest of the body, the skeleton and the muscles? How does this low gravity environment of a spaceship affects them? What's going on at a physiological level?

Mark - Well, because they aren't exercising in a normal way, and by that, I mean, when you normally exercise, you're walking or you're running, you have constant impact exercise, that's what helps bone turnover effectively. Because they haven't got that that they lose bone mineral density and the other thing they haven't got is gravity pulling blood into the tissues. So even when people have exercised in space, for example, just running on a treadmill with braces to hold them on it, they still lose bone mineral density and muscle mass because although they've got impact exercise, they haven't got the gravitational force pulling blood into their legs. So, those are the two things; It's blood flow and impact exercise that are required to maintain bone mineral density and muscle mass.

Kat - How does this affect the body because presumably, if things like muscle and bone are starting to breakdown, the components of those have to go somewhere?

Mark - Yeah and you gradually excrete the protein out and you gradually lose the calcium although it does differ in different parts of your body. So, the work that I was previously involved with was looking at, what happens to your head more than anything else. Your cranium actually tends to deposit more bone rather than lose it. So, it's not all loss. It's depending on where it is in your body that's changing.

Kat - So for example on our hypothetical nine month trip to the red planet going to Mars, we've already heard that just after a reasonably short trip into space, Stanley Love, he lost about eight pounds of muscle. How much would the average astronaut expect to lose?

Mark - Well, there's different studies, but on average, the studies seem to show that people lose between one per cent and 5 per cent of their bone mineral density per month that is during microgravity. That's quite a lot if you're going to be spending nine months traveling somewhere. We don't know whether it plateaus off and some of the evidence from the International Space Station suggests that it does. But if it's not going to plateau off, then you're obviously going to have quite a lot of loss before you arrive.

Graihagh - You can almost imagine - is someone just going to basically turn into a jellyfish? What would be the ultimate endpoint for this?

Kat - We don't really know but it's not really the fact that they might have a little bit of loss that will be okay. It's more of an emergency situation when they arrive at wherever they're going. You need to also maintain bone mineral density and muscle so you can run away or move and do the appropriate things even in the relatively reduced gravitational environment. So from a safety point of view, although people say if it's a one-way trip, does it matter or something like that? It does matter because actually, you may well need to do stuff when you get there.

Kat - So for example, just getting down from your rocket onto the surface of Mars, would there be a risk if you tripped and fell over you would just snap a bone like that?

Mark - We don't really know but that is a perceivable risk. And so, there's been a lot of work looking at countermeasures to try and minimise this bone mineral density and muscle mass changes.

Kat - What sort of things have you looked at? What sort of approaches can people take?

Mark - If you look at the old space lab missions and some of the stuff from the '80s and '90s, people used to exercise in space with braces over their shoulders holding onto a treadmill. That didn't really prevent bone mineral density and muscle mass changes because, although you're getting the impact of exercise again, because you haven't got blood being pulled into your legs, you still lost bone mineral density and muscle mass. So, some of the countermeasures that are now being suggested are things like lower body negative pressure where you sit in a chamber that sucks air out from around your legs as well as having a treadmill on the bottom, and then you've got effectively an artificial gravitational force across you, pulling blood into your legs and you've got impact stress. That seems to prevent bone mineral density and muscle mass changes. The problem with that is that it requires a bit of power and also constant vibrations which would affect things such as crystal experiments or other stuff that might be going on. And then another measure such as interlimb resistance devices where you use one leg as a resistance device against the other. There's things such as human power centrifuges where effectively, two bikes are set apart opposite each other and by exercising against each other, you can create a gravitational force as you spin around. But all these are quite big things. If you've got a roughly small craft during such a mission, it's going to be difficult to plan it into that. So there's lots of work going in this area. 

Kat - What about things like drugs and I'm sure I remember seeing a study about looking at how bears hibernate because they lose their muscle mass when they hibernate, but then they kind of get better again? What could we learn about maybe tweaking physiology with drugs or chemicals to help reduce these side effects?

Mark - It's interesting you say about when bears hibernate but even if you just lie down for a prolonged period, you lose bone mineral density and muscle mass. It happens in humans as well. We don't really know enough at the moment in terms of whether we can optimise things with hormonal treatments or with additional calcium and vitamin D and things like that. It does seem to be that really, to maintain bone mineral density and muscle mass, you have to be using them. And so, as drugs might offer a small benefit, it is unlikely to be the sole solution.