By Brady J. Holmer, @B_Holmer
Unlikely or not, it is interesting to ponder the physiological and technical challenges of a Martian marathon. Read our post from last week to learn why runners will be moving in giant leaps. Stride aside, how will the freezing cold, lack of oxygen, calorie requirements, and protective clothing affect the runners?
Cons of the Mars environment:
Temperature: beyond chilly
Race day conditions can be quite unpredictable even on Earth, and Mars will be no exception. Temperatures can vary from a moderate 70˚ F (20˚ C) around noon to an unbearable -195˚ F (125˚ C) at night. For the sake of this thought experiment, let’s assume that race day temperatures hover around the average of -67˚ F (-55˚ C).
At this temperature the blood vessels in many organs and leading to the skin will undergo profound constriction, reducing blood flow to areas where the runners don’t need it (that is, everything but the legs, brain, lungs, and heart). This conserves heat and maintains core body temperature as close to normal as possible.
Authors of a classic 1998 paper in Experimental Physiology demonstrated that this constriction can occur even at a “mild” temperature of 45˚F (7˚C) for just 90 minutes (1).
Exaggeration of this physiological response in instances of extreme cold (i.e. Mars) would occur due to a condition called non-freezing cold injury (2). Symptoms include damage to vascular tissue and heightened constriction of blood vessels. This means runners will have trouble providing oxygen-rich blood to their working muscles which will be in competition with the core to maintain a survivable temperature. Frostbite on Mars sounds disproportionally painful.
Another main concern of extreme cold exposure will be the detrimental effects of shivering thermogenesis, the body’s involuntary quivering of muscles to produce heat in an attempt to maintain core body temperature. To do this, the body must use fuel sources such as carbohydrate and fat. This also occurs at even relatively “mild” cold temperatures.
A study appearing in a 2005 issue of The Journal of Physiology exposed a group of men to a temperature of 41˚F (5˚C) for just 90 minutes and showed that utilization of glucose and glycogen increased five-fold from normal resting conditions (3). Muscle glycogen, our stored form of carbohydrate, contributed up to 60% of the total increase in heat production during just moderate-level shivering.
Exposure to Mars level cold would exacerbate these effects in runners and lead to a sacrifice of valuable fuel stores in an attempt to stay warm, leaving little for the marathon effort. In a race over 2 hours such as the marathon, fuel partitioning is key, and glycogen stores become important late into the race. Without fuel to provide energy for muscle contractions, performance will inevitably suffer, even if proper nutrition and “carbo-loading” are implemented.
Oxygen deprivation in the air
Given the vast difference in the composition of the air, breathing on Mars will also be difficult. The atmosphere of Mars is 95% carbon dioxide (CO2), meaning there is very little oxygen. Normally, CO2 is produced during high intensity exercise such as marathon running, but is counteracted by expiration, preventing accumulation of acidifying ions and the ensuing unpleasant burning feeling in the lungs and legs. In this regard, Mar’s atmospheric gas composition presents an ideal situation for the lung-torching turmoil that all runners fear late into the end miles of a marathon, although now, this will occur from the start. Even the most rigorous altitude training regimen won’t prepare Martian runners for the low-oxygen conditions they will experience. Well-designed spacesuits will need to be implemented to allow runners to inhale a gas composition that resembles one on Earth, while simultaneously helping to expire CO2 at a higher rate than usual.
Wreaking havoc with red blood cells
Let’s not forget about the radiation. Mars’ atmosphere is less dense than the Earth (approximately 100-fold less so), and radiation from the sun is much more potent. Spontaneous and largely unpredictable solar flares that decide to pop up during the marathon will send charged helium nuclei, neutrons, protons, and other dangerous and highly energetic particles coursing through the runner’s bodies. Exposure to one of these solar particle events during the Mars marathon would lead to the destruction of red blood cells (hemolysis) and along with it, the all-important, oxygen carrying hemoglobin molecules, oxidative stress, and damage to muscle fibers.
Runners will likely fall victim to a condition we might call “space anemia”. A study in Physiological Reports from 2017 investigated the response of the circulation to a head down tilt bed rest condition – used to simulate microgravity encountered in space – and found that it resulted in a loss of hemoglobin (4)! Hemoglobin is necessary to carry oxygen to sites of active muscle during running, and a reduction is associated with a lower exercise capacity.
Circulatory changes may be further exacerbated by the well-known detrimental effects that microgravity has on aerobic capacity. Indeed, researchers have used a model of sustained bed rest further compounded by low-oxygen space environments such as Mars, to investigate the effects on cardiovascular capacity.
Keramidas et al. demonstrated in a 2017 Experimental Physiology paper that just 10 days in this space-simulating condition impaired whole-body peak oxygen uptake (VO2peak) by 8% with an accompanying reduction in peak power output during an exercise test (5).
Furthermore, in 2018, Salvadego et al demonstrated in The Journal of Physiology that 21 days of hypoxic bed rest led to an 8% reduction in V02peak, a reduction in thigh muscle volume, and impairments in the body’s production of energy (mitochondrial respiration and aerobic metabolism) and an ability to match oxygen supply to demand during leg exercise (6).
These changes lead to a reduction in aerobic performance – and Mars runners will fight against all of these pathological changes as they try and complete the race as they find themselves starved of the ability to get crucial, oxygen rich blood to their working muscles during the race. This means that runners will be less capable of performing at their max capacity on race day.
So far, the prospects are looking quite grim for the runners. Will nutrition or protective suits be their saving grace? Find out on Friday in the final blog of our series.
- Weller et al. Physiological responses to moderate cold stress in man and the influence of prior prolonged exhaustive exercise. Experimental Physiology. 83 (1998); 679-695
- Tipton M.J. Environmental extremes: origins, consequences, and amelioration in humans. Experimental Physiology 101.1 (2016); 1-4
- Haman et al. Partitioning oxidative fuels during cold exposure in humans: muscle glycogen becomes dominant as shivering intensifies. The Journal of Physiology 566.1 (2005); 247-256
- Trudel et al. Hemolysis during and after 21 days of head-down-tilt bed rest. Physiological Reports. 5.24 (2017)
- Keramidas et al. LunHab: interactive effects of a 10-day sustained exposure to hypoxia and bedrest on aerobic exercise capacity in male lowlanders. Experimental Physiology 102.6 (2017); 694-710
- Salvadego et al. PlanHab: hypoxia does not worsen the impairment of skeletal muscle oxidative function induced by bed rest alone. The Journal of Physiology 000.00 (2018); 1-15