Use it or lose it in Space Missions...

Ben Hammond

MSc Space Physiology & Health; Human Performance Intern, McLaren Applied Technologies

With international space agencies and the real-life Tony Stark (Elon Musk) making huge advances in rocket technology, it is likely that within the next couple of decades humankind will touch down on Mars. However, this is only half the battle. The gravity on Mars is roughly one third as strong as Earth’s. You may be thinking “great, everything will require less effort”, and you’d be right, however, there is a huge caveat to that. As we’ve found from the results of time spent in space (the longest continuous period being 14.4 months), when people are exposed to levels of gravity lower than that on Earth, losses in muscle and bone occur; predominantly, in muscles which we continually use to walk and maintain our posture. You may have heard the expression ‘use it or lose it’ - hugely applicable here. These losses can increase astronauts’ risk of injury when returning to Earth by leaving them very weak and fragile. A return mission to Mars will take around 3 YEARS to complete, mainly because of the wait for the two planets to be close enough in proximity again to allow a relatively short journey home. That’s around 12 months in microgravity and around 26 months in Martian gravity. Now, it doesn’t take a rocket scientist to figure out that, based on the numbers, the outlook for muscle retention isn’t great. That being said, we‘re still pretty uninformed about the extent to which living on Mars will stimulate our muscles. 

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Me using a Lower Body Positive Pressure equipment

Recently, my colleagues and I conducted an investigation to try to shed some light on the matter. To do this properly, we needed to achieve two key things: 1) simulate walking in Mars gravity, 2) measure the activity in the muscles used for walking. With this, we compared the muscle activity produced while walking on Mars to that produced when walking on Earth, gauging the degree of muscle loss that we might expect for a mission to Mars and to inform countermeasures.
To simulate Mars gravity, we used a technique called lower body positive pressure (LBPP). There are a few different ways in which you can simulate partial gravity environments, but this one has fewer limitations than the rest. LBPP involves putting someone inside an air-tight inflatable box from the waist down. Through manipulation of the air pressure within, it can generate a lifting force, changing the weight of the person inside. Our device was designed and built by engineers at the John Ernsting Aerospace Physiology Laboratory at the Pontificia Universidade do Rio Grande do Sul (PUCRS) in Porto Alegre, Brazil. With a treadmill placed underneath, the participant could then walk in simulated Mars gravity. To measure the amount of activity inside the leg muscles, we then attached electrodes to the skin at each of the muscles we were interested in (a method called electromyography) which picked up an electrical signal that muscles give off when they are being worked. The more intense the signal, the more active that muscle is while walking.
What we found was quite unexpected. The results of our investigation suggested that there was no significant difference between the muscle activity observed while walking in Mars gravity and the muscle activity observed walking on Earth. If this were to be true, then it would not be foolish to think that we could use the 26 months on the Martian surface to reverse losses in muscle and bone suffered on the outward journey in preparation for the return trip. However, there were two important variables that we failed to account for in our experiment. These variables were stride length and stride frequency when walking. 

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Now, pretty much everyone has seen a video or animation of an astronaut walking on the moon. It looks a bit like they’re bouncing along doesn’t it? (Take a look at the NASA video of Apollo 17 astronauts Gene Cernan and Jack Schmitt walking on the Moon). This is because the gravity on the moon is so weak, that when you push your foot against the ground to propel you forwards and upwards to walk, there is far less gravitational force pulling you back down again. As a result, you don’t have to take strides as frequently and the distance that you travel with each step is far greater. 

The moon is smaller than Mars, and so there is even less gravity there, but the same principle applies. With this in mind, even if the results of our experiment were to be true and the walking muscles are getting just as much activity with each step on Mars as they are on Earth, theoretically, they will be used less often. Considering our ‘use it or lose it’ principle, this would still mean muscle and bone loss to a disabling degree in the absence of effective counter strategies; which are currently lacking. More studies need to be done around this area, accounting for all variables, to further our understanding of human performance on Mars and ensure the safety of our astronauts, or we’ll be keeping Elon Musk waiting at the launch pad!