You Don’t Have to Leave the Stratosphere to Feel Like You’ve Been in Space

view of Earth from space

Credit: iStock / Getty Images

Astronaut Scott Kelly came back from 340 days in space two inches taller. Along with height, many aspects of the body change because of the weightlessness environment of space. The body loses muscle, heart and bone mass because it no longer has to support itself as it does on Earth. There is also no feeling of “down” in space. The brain uses this signal for balance, so it has to change how it processes sensory information. While Kelly went to space to study the health impacts, scientists can investigate the effects without leaving the planet. Here are some of the ways scientists recreate weightlessness on Earth. Most of the studies are done for several days to several weeks.

Long-Duration Bed Rest

Study participants lie in bed 24 hours a day. In some studies, the bed tilts towards the head (referred to as head-down tilt, or HDT) to mimic the blood and fluid flow towards the head that happens in space.

Bed Rest

Dry Immersion

Study participants sit in a tub of water. This method takes advantage of water’s buoyancy to suspend participants similar to how they would float in space. Participants are wrapped in a waterproof cloth to keep them dry.Dry Immersion

Unilateral Limb Suspension

Study participants wear a platform shoe on one foot to keep the other foot off the ground. They balance and get around with crutches. This method focuses on how the muscles change in the hovering leg.

Lower Limb Suspension

Parabolic Flight

The airplane recreates the weightlessness of space by flying up and down in a wave pattern. Unlike the other methods, the suspended period is very short. Participants float in the air and feel weightless for about 20 seconds when the plane is changing directions to return towards the ground.

Findings from these studies on the health effects of the space environment will help astronauts prepare for long space missions such as going to Mars. For updates on space research, tune in to the National Academies’ Space Science Week March 29 through 31. Experts will share information about ongoing research programs and discuss issues and advances in their fields.

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.

Don’t Take a Load Off: Too Much Sitting Is Bad for You

Office Chair

If you’ve considered getting in on the standing desk trend, you’ve probably heard the public health warnings about the dangers of too much sitting. (Would you get a standing desk? Tell us on our poll.) Several studies report an increased risk of developing cardiovascular disease with too much sitting. The good news is you can prevent it. The key may be to keep the blood moving to combat the decreased blood flow caused by sitting.

Blood vessels are lined with cells called endothelial cells. Besides keeping the blood vessels healthy, endothelial cells make sure that blood goes where it needs to by releasing molecules that either enlarge or narrow the blood vessels. They constantly feel the force of the blood flowing over them, and changes in blood flow patterns, including decreased blood flow, can reduce their effectiveness. Impaired endothelial activity increases the risk of developing diseases that affect the blood vessels such as atherosclerosis (the buildup of cholesterol, fat and other substances within and along the walls of blood vessels).

A new study discussed in this AJP-Heart podcast examined whether sitting-related diminished blood flow impaired endothelial function. To do this, the researchers compared endothelial function in the leg of their study subjects—one leg’s blood flow was reduced from sitting while the other leg’s blood flow was maintained by placing the foot in a warm water bath. After a three-hour sitting session, the researchers found that the blood vessels in the leg of the dry foot did not dilate as well as before the session, a sign of impaired endothelial function. The blood vessels in the leg on the warm water side, however, were able to dilate normally. The researchers also confirmed that leg blood flow on the dry foot side was lower after the three hours of sitting while blood flow on the warm water side remained similar.

The researchers concluded that prolonged sitting caused endothelial dysfunction because blood flow through the legs decreased. The flip side was that maintaining blood flow—in this study with a warm water bath—prevented the decline in endothelial function.

What can you do to keep your blood flowing? Jaume Padilla, PhD, the study’s lead investigator, thinks even small amounts of physical activity can help. He tries to stand as much as possible during his work day. When he’s sitting for very long periods of time, such as during long flights, he finds ways to keep his legs moving (check out these leg and other stretches from Virgin Atlantic airline that you can do while sitting). Walks are good, too. Another study from Padilla’s group also showed that a short ten minute walk could restore blood vessel health and flow in people who were sitting for six hours.

Get up and move around regularly during your day. It’s all-around good for you.

Stacy Brooks & Maggie Kuo

Maggie KuoMaggie Kuo, PhD, is the former Communications and Social Media Coordinator for APS. Catch more of her writing in the Careers Section of Science Magazine.

Ice, Ice Baby: How Being in Cold Water Can Kill You


Credit: Barnyz / Flikr

Spring is coming, and if you like to welcome the crisp March weather with water sports such as fishing and kayaking, remember that lakes, streams and oceans can have freezing temperatures this time of year. Falling into icy water is never part of the plan, but it happens even to the best cold-water adventurers. Exposure to cold water is dangerous and sometimes fatal but not because of hypothermia—low body temperature—as you might expect. In fact, hypothermia takes about half an hour to occur. Most cold-water drownings happen for another reason.

Being in cold water activates two opposing physiological responses at the same time. One is called the cold shock response, which activates the fight-or-flight response, a series of hormonal changes that rev up your body in stressful situations. This cold shock response causes you to gasp and breathe faster, increase your heart rate and pump blood to your muscles so you can escape the icy water quickly.

But mammals (including humans) also experience an opposite response to being in water called the diving reflex. It starts when cold water touches the face, and it prepares the body for a long dive. This response slows your heart rate, helps your body save oxygen and sends blood away from your muscles to your heart and brain.

These contradictory signals cause extreme stress on the heart. While the cold shock response dramatically increases blood pressure and heart rate, the diving reflex sends signals to reduce blood pressure and slow heart rate. These confusing signals can lead to irregular heartbeats (arrhythmias) and drastic changes in blood pressure, which can cause heart attack and lead to drowning. This is especially a risk for people with preexisting heart disease.

Bottom line: Be careful around bodies of cold water, and if you have a heart condition, don’t swim in them. It’s also wise to always swim with a buddy and have someone nearby who knows CPR whenever you are in the water. Following these tips can help you enjoy the weather, not the emergency room, during this spring season.

Learn more about the physiology of drowning.

Emily Johnson

Emily Johnson, PhD, is an APS member and a former volunteer editor for the I Spy Physiology blog.

Kidney Trouble Could be a Downstream Consequence of the Flint Water Crisis

The water crisis in Flint, Mich., highlights the toxicity of lead. While the most publicized consequence of lead exposure are the long-term effects on developing brains, this toxic metal also damages the kidneys of adults and children. The people of Flint face a number of long-term health risks related to their current lead exposure, including chronic kidney disease. Adults in the area, especially those already facing kidney problems, may suffer acceleration of their health issues.

Flint Michigan

The exterior of the Flint Water Plant in Michigan. Credit: Getty Images

Lead reduces the kidneys’ ability to work properly, causing the kidneys to raise blood pressure, leak protein and eventually stop working altogether. Although the effects on the kidneys are well-known, how lead damaged the kidneys wasn’t clear until recently when a study in Environmental Health Perspectives revealed that the damage was actually done through another metal, iron.

Iron is found in red blood cells (RBCs) and allows RBCs to carry oxygen to the body. Normally, old or damaged RBCs are cleared out of circulation by the liver and spleen. Cells in these organs engulf or “eat” damaged RBCs and recycle them into new RBCs. Lead poisoning damages so many RBCs that the kidneys start clearing them, too. Scientists from Seoul National University in South Korea found that as the consumed RBCs broke down inside the kidney cells, iron got left behind.

The scientists first showed that kidney cells exposed to RBCs from people with lead poisoning did not grow as well as cells that weren’t exposed to lead-damaged RBCs. Exposing kidney cells to lead alone, though, did not harm them. When damaged RBCs were around, the kidney cells engulfed them, and the ingested RBCs deposited iron within the cells. Iron is a well-known toxin to kidney cells, so it appeared that the iron left by the lead-damaged RBCs, not lead itself, caused the kidney cells to die.

The scientists then examined rats that drank water with lead for 12 weeks. As expected, kidneys from the lead-exposed rats showed damage. The damaged kidney areas had iron deposits, further supporting that injured RBCs and the iron they left behind contributed to the scarring in the kidneys.

Currently, we have no way to clear iron from the kidneys. Further studies may produce new treatments for kidney damage from lead exposure. Of course, the best treatment is to get the lead out.

Pascale Lane

Pascale Lane, MD, is a pediatric nephrologist and professor at the Oklahoma University Health Sciences Center.

Running a Thousand Miles Can Be Exhausting. How Do Iditarod Sled Dogs Do It?

View of sled dog race on snow

Credit: iStock

Have you ever had a morning where you just did not have the energy to go out for your five-mile run? What if you woke up in New York City and had to run to Miami? That is the distance Alaskan Huskies run every year at the annual Iditarod sled dog race. How these amazing canine athletes accomplish this feat is interesting to scientists because it provides insight into how human performance can be maintained in challenging conditions.

Muscles get energy to exercise from glucose (sugar) and fats stored in the body. Muscles use oxygen from the air to transform the two into energy. Scientists originally assumed that the Alaskan Huskies used fat to sustain long periods of exercise. Huskies are fed a diet rich in fat, and the body stores fat in greater quantities than glucose. However, a recent study found that the dogs actually used glucose to sustain exercise and that the glucose was made from a part of fat called glycerol. The dogs took advantage of their fat stores, but they used the fat stores to make glucose.

Why go through the trouble of turning a part of fat into glucose rather than using fat as is?  That answer is not entirely clear yet, but one possibility is that the dogs typically run the Iditarod at an average of 10 miles per hour, or six-minute miles, while pulling a sled. Muscles prefer glucose to fuel intense exercise because they can get more energy out of it for every molecule of oxygen breathed in. Sustaining such high speeds while pulling a load may require the use of glucose over fat. This is not to say that fat is not important for the dogs. As mentioned, the dogs use the fat, just not directly, and fat is good fuel during rest periods and recovery between running.

The Alaskan Huskies were bred to perform these amazing endurance feats, but we don’t know yet if human muscles can invoke the same rate of fat-to-glucose conversion processes to fuel exercise of such long distance. However, humans performing at such high speeds for prolonged periods would most likely need to do this same type of conversion.

Next time you’re not up for your morning run, channel your inner sled dog: Five miles really isn’t that bad.

Benjamin Miller, PhD, is an associate professor in the Department of Health and Exercise Science at Colorado State University. He co-directs the Translational Research in Aging and Chronic Disease (TRACD) Laboratory with Karyn Hamilton, PhD.

Ben Miller with sled dog

Dr. Miller with study participant.