Some muscles deteriorate slower than others in space

Chuck Bednar for redOrbit.com – @BednarChuck

During prolonged periods of space travel, the muscles used by astronauts to chew food are likely to hold-up better than those required for walking, according to a new study appearing in the July edition of The FASEB Journal that investigated muscle deterioration in mice.

Dr. Elizabeth Barton of the College of Health and Human Performance, Applied Physiology and Kinesiology at the University of Florida, and her colleagues explained that while muscles do tend to weaken when in microgravity environments because they need gravity resistance to remain healthy, some types of muscles are more affected than others.

They found that cheek muscles used for mastication do not experience the same type of atrophy in space that leg muscles due. Even when a person is not actually actively chewing food on a regular basis, only some of parts of the muscle undergo the same types of changes the leg muscles experience, allowing them to remain relatively healthy on the whole.

The discovery appears to indicate that different muscles have different “set-points” for regulating muscle mass. The findings could benefit not only astronauts but anyone else in a low-resistant environment, including those required to spent extended periods of time confined to a hospital bed or those working long hours at a sedentary job each day.

Studying muscle differences in space mice and Earth mice

“Maintaining muscle mass and good muscle repair is key to all areas of our lives: successful aging, combatting devastating diseases like muscular dystrophy, as well as generalized health and well-being to improve quality of life,” explained Dr. Barton. “Figuring out these pathways may lead to strategies that can enhance training effects for healthy individuals.”

As part of their research, she and her fellow scientists used two different groups of mice – one rode on the STS-135 space shuttle mission for two weeks (lucky mice), and another that remained on the ground. The leg muscles of the space mice experienced to resistance because of gravitational weightlessness, but their cheek muscles continued to be used for chewing food.

After the experiment, the researchers measured the muscles of each group, and found that while the leg muscles of the space mice had lost mass when compared to the Earth mice, their cheek muscles had not. In addition, the cellular signals controlling muscle size were vastly different in the muscle groups of the space mice, indicating that the cheek muscles regulate their mass in a different way than the leg muscles do.

Next, they switched the space mice to a liquid diet so the cheek muscles would not have to chew, and thus would be freed of any load or resistance. The authors tested how the signals had been altered as a result, and found that only part of them had changed in a way similar to the way that the leg muscles had. As a result, the muscles remained in relatively good health.

“Research like this will help humans go farther into space than ever before, but the most profound impact will be here on the ground,” said Dr. Gerald Weissmann, editor-in-chief of The FASEB Journal. “The process that causes astronauts’ muscles to waste away in space is the same as that which causes inactive people to lose muscle mass on Earth. Muscles like those in the cheek may serve as a guide to preserving other muscles, not only against microgravity in space, but also inactivity on Earth.”

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