Lift Weights to Lower Blood Sugar?

Red-White_muscleSRxA’s Word on Health was interested to read that researchers in the Life Sciences Institute at the University of Michigan have overturned a long-held belief that whitening of skeletal muscle in diabetes is harmful.  Instead, they found that the white muscle that increases with resistance training, age and diabetes actually helps to keep blood sugar in check.

The insights identified in the study may point the way to potential drug targets for obesity and metabolic disease.

We wanted to figure out the relationship between muscle types and body metabolism, how the muscles were made, and also what kind of influence they have on diseases like type 2 diabetes,” said Jiandie Lin, Life Sciences Institute faculty member.

Much like poultry has light and dark meat, mammals have a range of muscles: red, white and those in between. Red muscle, which gets its color in part from mitochondria, prevails in people who engage in endurance training, such as marathon runners. White muscle dominates in the bodies of weightlifters and sprinters – people who require short, intense bursts of energy.

lifting-weightsWhen you exercise, nerves signal your muscles to contract, and the muscle needs energy. In response to a signal to lift a heavy weight, white muscles use glycogen to generate adenosine triphosphate (ATP) – energy the cells can use to complete the task. While this process can produce a lot of power for a short time, the glycogen fuel soon depletes.

However, if the brain tells the muscle to run a slow and steady long-distance race, the mitochondria in red muscles primarily use fat oxidation instead of glycogen breakdown to generate ATP. The supply of energy lasts much longer but doesn’t provide the burst of strength that comes from Paula_Radciffe_NYC_Marathon_2008_croppedglycolysis.

People with diabetes see whitening of the mix of muscle.

For a long time, the red-to-white shift was thought to make muscle less responsive to insulin, a hormone that lowers blood sugar,” Lin said. “But this idea is far from proven. You lose red muscle when you age or develop diabetes, but is that really the culprit?”

To find out, the team set out to find a protein that drives the formation of white muscle. They identified a list of candidate proteins that were prevalent in white muscle but not in red.

mouse weight liftingFurther studies led the team to focus on a protein called BAF60c, a sort of “zip code” mechanism that tells the cells when and how to express certain genes. The Lin team made a transgenic mouse model to increase BAF60c only in the skeletal muscle. One of the first things they noticed was that mice with more BAF60c had muscles that looked paler.

“That was a good hint that we were going in the white-muscle direction,” said lead author Zhuo-xian Meng, a research fellow in Lin’s lab.

They used electron microscopy to see the abundance of mitochondria within the muscle, and confirmed that muscle from BAF60c transgenic mice had less mitochondria than the normal controls.

We saw predicted changes in molecular markers, but the ultimate test would be seeing how the mouse could run,” Lin said.

treadmill mouseIf the BAF60c mice could run powerfully for short distances but tired quickly, the scientists would be able to confirm that the BAF60c pathway was a key part of the creation of white muscle.

Using mouse treadmills, they compared the endurance of BAF60c mice to a control group of normal mice, and found that the BAF60c transgenic mice could only run about 60% of the time that the control group could before tiring.

“White muscle uses glycogen, and the transgenic mice depleted their muscles’ supplies of glycogen very quickly,” Lin said.

After some follow-up experiments to figure out exactly which molecules were controlled by BAF60c, Lin and his team were confident that they had identified major players responsible for promoting white muscle formation.

Now that they knew how to make more white muscle in animals, they wanted to determine whether white muscle was a deleterious or an adaptive characteristic of diabetes.

obese mouseThe team induced obesity in mice by feeding them a “Super Size Me” mouse diet. On a high-fat diet, a mouse will double its body weight in two to three months. They found that obese mice with BAF60c transgene were much better at controlling blood glucose.

The results are a bit of a surprise to many people,” Lin said. “It really points to the complexity in thinking about muscle metabolism and diabetes.”

In humans, resistance training promotes the growth of white muscle and helps in lowering blood glucose. If future studies in humans determine that the BAF60c pathway is indeed the way in which cells form white muscle and in turn optimize metabolic function, the finding could lead to researching the pathway as a drug target.

We know that this molecular pathway also works in human cells. The real challenge is to find a way to target these factors,” Lin said.

Until we know for sure SRxA’s Word on Health recommends a healthy mix of running and weight training.

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Wheezing: Whining or Winning?

Many people with asthma avoid exercise because they’re afraid it could trigger symptoms such as shortness of breath, wheezing or a full-blown asthma attack.

However, a new report from The Cochrane Library turns these fears on their head. The authors conclude that not only is it safe for people with asthma to exercise, but it could also reduce their risk of asthma symptoms or attacks!

Study author, Kristin Carson, from The Queen Elizabeth Hospital, Clinical Practice Unit, Adelaide, Australia explains that over time patients with asthma who avoid exercise can become out of shape, losing muscle mass and cardiovascular fitness. That makes any future attempts at physical activity significantly harder, increasing the chances that patients will become fatigued and breathless and further discouraging physical activity. “This results in a spiraling cycle,” she says, in which patients are even more likely to avoid exercise.

To determine whether exercise was a danger to asthmatics, Carson and her colleagues reviewed previous studies that looked at the effects of physical training on people with asthma comparing patients who received no or minimal physical activity to those who exercised for at least 20 minutes, twice a week, over the course of four weeks.

The researchers found that the patients who had exercised, using physical training such as running outdoors or on a treadmill, cycling, swimming or circuit training were no more likely to have a serious asthma-related problem than those who weren’t exercising or who did light exercising such as yoga.

The patients who exercised also improved their cardiovascular fitness, which in turn can reduce asthma symptoms over time. There was also some evidence to suggest that exercise improved patients’ quality of life.

We found no reason for people with stable asthma to refrain from regular exercise,” Carson said. “Physicians should encourage their patents with stable asthma to engage in physical training programs.”

Even though this research suggests that exercise is safe for asthmatics, we suspect that many people will still think they can use their asthma as a reason to avoid physical activity.

Well now there is no excuse, and just in case you’re in any doubt consider the following list of people who never let asthma stop them:

Do you have any asthma and exercise stories to share?