Scientists are studying black bears and their ability to change their metabolism greatly during hibernation. Not only does their body temperature drop, but their metabolism decreases by about 75 percent when they are hibernating. Black bears can go up to 100 days without eating or drinking during their annual down time. They also can last the same period without urinating, defecating, or exercising. Bears can reduce their metabolic rate during winter slumbering because of their warm fur and their body mass to surface area ratio is good for heat retention. A University of Iowa researcher studying black bears found one with a heart rate of eight beats per minute when it was in deep hibernation. Before hibernation it had a sleeping heart rate of 40-50 beats per minute.
During hibernation black bears were found to also have the ability to preserve their bone and muscle mass. Calcium from waste is used to keep bones from weakening. Scientists haven’t figured out how they keep their muscles from deteriorating though.
So how do these bear attributes relate to human space travel? Humans do lose bone density and muscle during long periods of inactivity, and space travel occurs in a weightless environment, so bones and muscle are not actively resisting gravity in the way they are on Earth. Even with calcium supplementation, there is bone loss in astronauts, particularly in the legs. The longer a space flight lasts, the more potential bone loss there is. Even after five years back on Earth, some bones in astronauts had not recovered from the loss resulting from space travel. In space the extra calcium supplements, combined with the extra sodium found in packaged space foods can increase the risk of kidney stones.
Astronauts can also lose one to ten percent of their muscle mass while traveling in space. Even with exercise like riding a stationary bike or running on a treadmill, they still lose muscle and strength. A study of astronauts on the International Space Station found that after 180 days they had lost more than 40 percent of their physical work capacity, even with exercise. After returning to Earth, their muscle tone was that of an 80-year-old. On a round-trip mission to Mars, after three years of space travel, astronauts would be so weak they would barely be able to crawl. NASA is working on the possibility of developing a pill that would stop or at least reduce muscle loss while in space.
The black bear research may yield insights that help create medications that can maintain bone and muscle strength that is critical to the health and functioning of human astronauts during both short and long space flights. It may also help inform strategies for conserving food during periods when astronauts are kept in a state of relative immobility when they have nothing to do but wait.
Image Credit: Alan Vernon