Many mammals are able to build new muscles as they hibernate, leading some medical researchers to question why humans are not able to carry out the same biological functions.
Ground squirrels are one of the types of animal able to hibernate all winter, and emerge from their dens, immediately ready to scamper around the ground, and scrounge for food. Study of some of the animals revealed their muscles start to build late in winter, before the creatures wake up from their extended slumber.
Ictidomys tridecemlineatus, a North American rodent commonly known as the thirteen-lined ground squirrel, is noted for distinctive stripes. At the start of the hibernation season, these squirrels curl up into a tiny ball, and their body temperatures drop to match the environment. Although their heartbeat and breathing drops to near imperceptible levels, the bodies periodically warm up for around 12 hours once every one or two weeks.
Researchers weighed six members of the species, and performed ten full body MRI scans of the creatures over the course of an entire season. Over the course of hibernation, the squirrels were found to lose an average of 40 percent of their original body weights. Examination of muscles in the front and hind legs of the animals revealed they became stronger near the end of the hibernation cycle.
Molecular markers placed in the squirrels revealed that around two months before the rodents reached their minimum weight in April, leg muscles began to rebuild after a period of decline. This period was accompanied by production of proteins in new muscle tissue at a level equal to that seen at the height of summer.
Human beings traveling to Mars and beyond will be subject to long periods of microgravity. Long periods of time in space such as these can result in muscles atrophying from disuse.
Allyson Hindle led the research while she was at the University of Colorado, although the researcher is currently working at Massachusetts General Hospital. Soon after completing the study, Hindle learned that researchers at the University of Wisconsin had completed a similar studies, reaching a nearly-identical result.
Now that Hindle and her team have identified muscle growth in hibernating ground squirrels, future research could examine how the process occurs. From there, it may, one day, be possible to design new techniques to treat atrophy of muscles in humans, including deep-space astronauts and physically challenged individuals here on Earth.
Investigation of squirrels and how their muscles react to hibernation was profiled in the Journal of Experimental Biology.
