2016’s Ten Most Read Posts

It’s been a physiology-full 2016 on the I Spy Physiology blog! From exercise to respiration to heart health and beyond, we’ve explored how the bodies of humans and other animals work, adapt and react. Today, we take a look back at our 10 most read posts of the year.

Concussions among football players was headline news in 2016. Against this backdrop, our most popular post of the year looked at how woodpeckers can bang their heads roughly 12,000 times a day at a greater force than the average football hit without sustaining a head injury. Posts about the amazing endurance of Iditarod sled dogs and a researcher’s excellent explanation of what physiology is and why it’s important round out the top three. Check out this year’s top 10:

If you’ve got a topic that you’d like us to cover in 2017, we’d love to hear from you! Share your thoughts in the comments or send us an email.

Stacy Brooks

The Young Qualities of Old Muscle

Senior Adults Taking Spin Class

Credit: iStock

Decline, decrease, deteriorate—all words associated with the aging process. Preventing “D” words is important to keep older people healthy. The loss of muscle is one of the most obvious age-related decreases we experience. Bulky muscles on a person that lifts a lot of weights or the sleek tone of a person that runs a lot of miles shows you that muscles of young people are amazing in their ability to change with the demands put on them. Scientists call this ability to change “plasticity.” When and why does muscle plasticity decline?

As individuals age, large muscle fibers that allow explosive types of movements, such as jumping or lifting a heavy weight, disappear more than small muscle fibers that allow slow, low-force movements such as grabbing a cup or adjusting posture. A recent Journal of Applied Physiology podcast discusses a research article that looked at small, medium and large muscle fibers from a group of subjects who were ages 87 to 90. At this age a substantial decline in strength is expected. However, the study showed that even though large muscle fibers are lost in old age, medium-sized muscle fibers become very strong for their size to compensate for that loss. The amount of force the medium-sized fibers could generate for their size was greater than muscle fibers from a group of young subjects and was similar to a world-class sprinting athlete. Therefore, the medium-sized fibers in the muscle of a very old group of subjects were plastic and adapted to the loss of bigger more explosive muscle fibers.

Future research is needed to determine if this plasticity is apparent in all old individuals or whether it was unique to this group that was still fairly active. Also, it is still unknown why some types of fibers keep this plasticity and others do not. Although older muscle does decline, decrease and deteriorate, plasticity appears to remain, which provides an interesting avenue to prevent the “D” words.

Ben MillerBenjamin 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.

To Play Better, Skip the Post-Game Drink

Sports and alcohol are a famous pair. Whether you’re a fan or an athlete, it’s common to follow up a great game with a drink or two. But does that drink affect your recovery after your workout? Researchers at California Polytechnic State University think that it might.

Rafael Jimenez, Amy Engel and a team of scientists studied this question by exercising rats for 60–90 minutes, then giving some of them ethanol, which is the type of alcohol found in alcoholic beverages. It was a heavy dose of alcohol, Jimenez says, noting that in other studies the dose produced a blood alcohol content of about 0.27 percent. (That’s equivalent to a 140-lb. man having about 9–10 drinks.) Three hours after the rats’ intoxication, the researchers measured the expression of recovery proteins in the rats’ muscles.

In particular, they measured the expression of PGC-1α, an important gene involved with the cell’s recovery response to exercise. PGC-1α is a major player in the creation of new mitochondria—the “engines” that provide cells with energy.

The expression of PGC-1α in muscle cells increased in all the rats after exercise. However, this increase was blunted in the rats that received ethanol. These findings are preliminary, but they suggest that drinking after exercise impairs recovery by keeping the cells from making more mitochondria. So next time you have a great workout, celebrate with a virgin margarita instead of an alcoholic drink to optimize recovery.

Emily Johnson, PhD

Emily Johnson EB Post-Game Drink

Study authors Rafael Jimenez and Amy Engel present their poster “Effect of post-exercise ethanol on signaling pathways regulating mitochondrial biogenesis” at the Experimental Biology 2016 meeting in San Diego. Credit: Emily Johnson

 

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.

Feeling Lightheaded after Exercise? Use the Heart in Your Legs!

Halliwill_stockphoto

John Halliwill, PhD

Do you ever get lightheaded or feel a little dizzy after hard exercise? Maybe you have felt a little bit of “tunnel vision” after a hard sprint or when you stand up in the first hour after a long training session? This is a surprisingly common occurrence in healthy people, as recently reviewed in the European Journal of Applied Physiology. Physiology can help you understand how to use the “heart in your legs” to pump away those symptoms.

You probably know that the heart is a pump and it works to keep blood moving around your body to supply your brain, your muscles and other body organs with oxygen and nutrients. When you perform exercise, such as walking, running and biking, the heart is also being helped out by another pump—the muscle pump—which is like having a second heart in your legs.

How does that work? When we exercise, with every step, stride or pedal stroke, the muscles in our legs compress the blood vessels that pass through them. This compression pumps blood from the legs, moving it back to the heart and greatly assisting the ability of the heart to move blood around your body. But when we stop moving, like at the end of exercise or while resting from a hard workout, lots of blood flows into the legs but doesn’t get the extra push from flexing muscles to move back toward the heart. This makes us susceptible to feeling lightheaded when standing up.

Be active, and be pro-active! Don’t skip the workout, but definitely remember to cool down. A cool down of easy activity keeps the muscles pumping blood back to the heart and helps maintain blood flow to your brain. After your cool down, if you happen to feel a little lightheaded, just flex your leg muscles to turn on the pump in your legs to give blood an extra boost back to the heart and to your brain.

John Halliwill, PhD is a professor of human physiology at the University of Oregon.

What Makes You Move?

The muscles in our body contract and relax to walk and move us through our day. Even when we are not in motion, our muscles are actively working to keep us upright and steady. Surprisingly, this constant action doesn’t fatigue us like running at top speed for 30 seconds does. What is the physiological basis for why some activities exhaust us while others we don’t even register?

Muscles are made up of three types of fibers identified by how quickly they contract: slow, fast or super-fast. Besides contraction speed differences, the fibers fuel themselves differently—either through oxygen, glucose (sugar) or both. They also range in size, amount of power they produce and how quickly they get tired. Every muscle group in the body contains all three types but the proportions of each reflect the muscle’s purpose.

  • Slow-contracting fibers derive their energy mainly from oxygen. They are resistant to fatigue and can contract for long periods of time. Muscles in the back contain a large number of slow fibers, which help sustain an upright posture for extended periods.
  • Super-fast fibers get their energy mostly from glucose stores in the body. These fibers are larger in diameter than slow fibers and, because of their size, can generate more powerful contractions. However, super-fast fibers exhaust quickly. Muscles in the arms have more of these fibers, enabling them to produce large amounts of tension quickly, as when lifting objects.
  • Fast-contracting fibers use both oxygen and glucose for energy. The size and fatigue rate of these fibers are in between the other two.

Just as fiber makeup varies between muscle groups, it also varies between individuals and can reflect the sports a person is best suited for. Marathon runners, who run for extended periods of time, have a large number of slow fibers in their quadriceps. Sprinters, on the other hand, need quick bursts of power and have a large number of fast oxygen/glucose-using fibers in theirs.

Former World Champion sprinter Colin Jackson. Credit: Guy Evans

Former world champion sprinter Colin Jackson. Credit: Guy Evans/Flickr

A recent study in Journal of Applied Physiology looked at the fiber makeup of the quadricep of former world champion sprinter Colin Jackson. The investigators found that Jackson has a high number of the super-fast glucose-using fibers, which was surprising to them because other elite sprinters studied have very few. The researchers noted that animals that sprint, such as cheetahs and horses, also have a high percentage of these super-fast fibers and suggested that sprinting ability could be partly related to the number of these fibers. Jackson’s unique muscle profile “provides a scientific basis for the high level of sprinting success he achieved during his career,” the researchers stated.

Maggie Kuo

Reviewed by Scott Trappe, PhD