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Muscle Fatigue May Be Caused by Calcium Loss

New research from Columbia University in New York shows that muscle fatigue during and after exercise may be caused by loss of calcium from muscle cells and that drugs that block the release of calcium from muscle cells may prolong endurance (Proceedings of the National Academy of Sciences, February 11, 2008).

When you exercise, your cells use food to generate electricity that causes nerves to send messages and muscles to contract. The energy from food generates electricity by driving minerals inside and outside of the cells, creating an imbalance of the minerals between the outside and inside of cells that causes electrons (electricity) to flow. A major source of this flow of electrons is from muscle cells pushing calcium outside their cell walls. This paper shows that muscles lose calcium continuously during exercise, and eventually do not have enough calcium to continue pumping calcium outside of cells, and therefore cannot generate as much electricity. This causes the muscles to weaken, hurt, lose coordination and feel tired.

The authors timed mice exercising to the point of exhaustion. Then they gave the mice an experimental drug that blocks the loss of calcium from muscle cells, and they were able to exercise longer. The researchers demonstrated the same process of calcium loss in the muscles of trained cyclists. However, they have not taken the next step of testing the drug to see if it improved endurance, because the drug has not been approved for use in humans.


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Dear Dr. Mirkin: Should I exercise less intensely when air pollution is high?

Researchers at University of Dublin asked whether a person would absorb more pollutants while walking or cycling slowly, or while covering the same distance at a faster rate. You would think that the faster you move, the harder you breathe, causing you to absorb more pollutants through your lungs. However, the opposite is true. Cycling and walking at a faster speed causes you to breath at a higher rate over a shorter duration of exposure. This results in lower total absorption of pollutants than cycling or walking the same distance at a slower speed (Journal of Environmental Science and Health, November 2007). The reduction was greater at lower concentrations of pollutants than at high concentrations, and was more marked in walkers than in cyclists. They found that fast walking decreased absorption of pollutants by 26 percent compared to walking slowly, while cycling fast decreased absorption by 17 percent over slow cycling .


Dear Dr. Mirkin: Do artificial sweeteners cause weight gain?

A study of 9514 middle-aged Americans from the University of Minnesota showed that those that drank diet sodas regularly were at high risk for developing diabetes in later life (Circulation, February 2008). How can this be? Diet drinks do not contain sugar, and it is a high rise in blood sugar after meals that markedly increases a person's chances of developing diabetes. But who is most likely to drink diet sodas? A person who is overweight and trying to lose weight. So the study does not show that diet sodas cause diabetes. It shows that people who try the hardest to lose weight (and often fail) are the ones most likely to drink diet soda.

However, researchers at Purdue University showed that mice fed artificial sweeteners ate more and put on weight. They believe that a sweet taste causes the brain to seek out more food (Behavioral Neuroscience, February, 2008). The authors propose that: "a sweet taste in the mouth helps prime the metabolism for the arrival of a calorie-heavy, sweet meal into the digestive system." This study needs to be repeated with humans to see if the sweet taste from artificial sweeteners actually causes people to eat more.


Recipe of the Week

Shrimp Confetti Chowder

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June 25th, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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