Conversations with Tobias Weber and David Green: Keeping fit in interplanetary hypogravity

We’ve all seen images of astronauts exercising in space. Smiling and genial people, breaking a sweat, jogging while attached to the apparatus. Maybe they’re doing some resistance training, stretching glorified rubber bands, or doing squats with resistance-based weights. Keeping fit in non-Earth gravity conditions takes some doing. That’s without even mentioning how the body reacts to different gravity levels in low orbit, space, on the moon, or one day, on Mars.

On the average, scientists tend to be forward looking and this goes for the field of exercising in space as well. Current exercise regimens on the ISS are adequate but there is definitely room for improvement, especially considering our ever improving knowledge of how the body reacts to spending time in space, if if it’s just lower earth orbit.

Tobias Weber and David Green have spent time investigating what exercise regimens would best suit the hypogravitational conditions likely to be experienced during inter-planetary travel. They took time to discuss their research with SCINQ.

SCIENTIFIC INQUIRER: Can we start off with some basic information. How does gravity differ in space? For example, on the International Space Station, the moon, Mars, deep space, etc.

TOBIAS WEBER: Well in fact, gravity is a universal force that exists in the entire Universe whenever there are things with mass or energy. This implies that the gravity levels experienced on the surface of any celestial body depends on its mass. On the Moon the Apollo astronauts experienced about 17% of Earth’s gravity level and when sometime in the future astronauts will set foot on Mars they will be exposed to 38% of Earth’s gravity. The fact the astronauts on the International Space Station seem to not experience gravity and can freely float through the different modules is due to the fact that the ISS orbits the Earth with a velocity of about 27500 km/h and is so to say in a constant ‘free fall’.

DAVID GREEN: However, the ISS is slowly decelerating and losing altitude plus vibrations can be passed through the station so that’s why we call it ‘microgravity’. If the ISS would stand still, it would simply crash on its surface like all other objects as in fact based on distance the ISS experiences around 93% of Earth’s gravity.

SI: How does this affect the human body? What exactly happens during the deconditioning of the musculoskeletal and cardiovascular systems?

TW: Basically all physiological systems appear to some extent gravity-sensitive and are affected by changing gravity conditions. There are short and long-term effects, meaning that some physiological adaptations such as a body fluid shifts occur immediately after changes of gravity levels and some others such as musculoskeletal adaptations happen over a period of weeks or months. To summarise all physiological effects of microgravity and hypogravity (e.g. Moon and Mars gravity) is probably beyond the scope of this interview but it is safe to say that to a certain degree all physiological systems are affected by gravity changes. One has to remember that the anatomy and physiological functions of all living beings have been fine-tuned through billions of years of evolution in 1g. Thus, when gravity levels change it will create some confusion before a new physiological equilibrium is found.

The problem is not so much the adaptation that occurs in space – the human body adapts and functions remarkably well in microgravity – it is more the sudden change of gravity levels (e.g. leaving Earth orbit and re-entry into the atmosphere) that can lead to problems and that require medical attention.

DG: Of course a return to Earth places the astronauts in an environment where if not immediately (we currently land in the middle of Kazakhstan) physical support and health care can be provided although a ballistic re-entry on Soyuz is not an ideal ambulance ride. However, even these capabilities will not be available on a mission to the Moon or Mars.

SI: What are the current exercise regimens on the ISS like?

TW: Astronauts exercise approximately 90min/day and they do a form of a concurrent exercise. Their program is prescribed by ESA’s exercise specialists and it consists of cycle-ergometry, treadmill running and conventional resistive exercise.

DG: A key aspect is that for some crewmembers the exercise appears to protect from significant de-conditioning , whilst in others it appears less effective. We do not know why, but this would be extremely valuable to understand or even better, predict. The other big issue is that the exercise regime on the ISS is resource consuming, resources that will not be available to us on a mission to the Moon or beyond. Thus we must get not only better, but more efficient as we will have less.

SI: Why did you decide to investigate plyometric exercises in zero gravity environments?

TW: It is known that plyometric exercise leads to high reaction forces that act upon the musculoskeletal system. And since reaction forces are greatly reduced in micro- and hypo-gravity, plyometric exercise seems to be a very promising exercise modality to compensate for the ‘lack’ of gravity and to provide an adequate stimulus to maintain musculoskeletal integrity. Plyometric exercise was recently tested in an ESA-funded 60 day bed rest (a ground-based analogue to simulate the physiological effects of microgravity) study and their results look very promising. They showed that a daily bout of 3-5 minutes of plyometric hops could prevent bone and muscle degradation and even maintain cardiorespiratory fitness.

DG: The fact that this hopping – that was performed horizontally within a sledge jump system – was so effective and yet took so little time is very encouraging. Also whilst hopping/jumping in a space vehicle would have to dampen the resulting forces, hence the use of a sledge system. However, on the Moon or Mars one could just hop, or jump ‘naturally’. In fact we are currently investigating how high, without being encumbered by an EVA space suit. It may be that hopping in a Lunar habitat is part of the future.

SI: How did you design your study? What special instruments did you use?

TW: We used a verticalised treadmill. When running on a verticalised treadmill one basically runs on the wall while one’s body is suspended through a suspension system. The force that pulls the user towards the treadmill can be adjusted and we tested different gravity levels starting from Moon gravity and going up to 0.7g. For this specific study we asked our study participants to perform plyometric hops and we measured the ground reaction forces.

DG: We measured ground reaction forces using the load cells within the verticalised treadmill but also compared them to novel insole technology. In fact we are currently finalising a paper showing that the insoles are an excellent alternative and thus may be suitable for use in analogues of the Moon and Mars where moving over dusty uneven surfaces are replicated, or even perhaps on the Moon itself!

SI: What did you learn? What advantages of plyometric exercises?

TW: Our study demonstrated that during plyometric hops in simulated hyopgravity peak reaction forces and flight time are scaled to hopping height. This means that performing plyometric hops in hypogravity can generate reaction forces that are equal to or even larger than reaction forces on Earth during walking and running. Plyometric hopping could therefore constitute a low-cost and effective countermeasure to offset the effects of reduced gravity on the Moon or on Mars.

DG: Our findings represent critical new information suggesting that hopping may be an valuable component of the exercise countermeasures package we use on the Moon.

SI: Can we discuss a hypothetical gym on the moon? What would it be like with current exercise regimens? How would a gym designed for plyometric exercises differ?

TW: Provided we can backup our results through a follow-up study, a moon gym could look fairly simple: One solution would be to hop/jump on the spot inside a habitat with sufficient head space so that astronauts could perform hops with maximal effort and another solution could be to use elastic bands to attach astronauts on the ground if performing high jumps would be too risky. Based on Newtonian mechanics one can expect that maximal jumps in lunar gravity could be 4m and higher.

DG: However, we do not know if 4m high jumps are really possible, and whatever the actual height, flight times will be long which might make controlling the body difficult. In fact it is critical to know whether landing can be controlled and the forces associated with it as we do not want to risk injury on the Moon.

SI: What is the next step toward implementing/adoption of plyometric exercises in space?

TW: We are currently preparing a study in Houston where we want to use NASA’s robotically controlled off-loading system. We want to try to perform jumps with maximal effort in lunar and Martian gravity and we want to study kinematics and kinetics in-depth using state-of-the-art biomechanical equipment.

DG: We are excited about the prospect of using NASA’s Active Response Gravity Offload System (ARGOS) system to test jumping in partial gravity whilst also investigating on how we might walk and run when not wearing an EVA suit as ultimately we want to design suits that enable normal partial gravity locomotion to be preserved.

For more information regarding Tobias Weber and David Green’s work follow the European Space Agency European Astronaut Centre on Twitter @ESA_EAC or visit the ESA European Astronaut Centre.

IMAGE SOURCE: Creative Commons

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