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Intense Training Maintains Endurance in Older People

Last Saturday, a 75-year-old man and a 69-year-old woman rode a tandem at the Sebring Tandem Rally, covering 51 miles at an average speed of 18.9 miles per hour. We used all the energy we had trying to stay with the bikes in front of us.

You lose power and strength with aging, but you keep most of your endurance. The limiting factor to how fast you can run or ride a bicycle is the time that it takes to move oxygen from your lungs into your muscles. This is measured with a test called VO2max. The higher the number, the faster you move oxygen into muscles.

Dave Costill of Ball State University studied marathon runners in their prime in the late 1960s and then again 25 years later. In 1970, Derek Clayton of Australia held the world record in the marathon at 2 hours and 8 minutes. In 1992, his orthopedic problems limited his running to 3-4 very fast miles per day. His VO2 max remained the same. His maximum heart rate slowed from 188 beats per minute at age 28 to 176 at age 50. He gained only 2 kilograms of weight going from 73.1 kg to 75.2. Other world class marathon runners who continued competing over the 25 years had an average drop in their VO2 max from 70 down to 65, a small reduction.

The world records for the marathon and mile for all ages are less than 10 percent slower for 50-year-olds, and a rapid decline in age group world records starts only after age 70. This applies to both men and women.

You have to work gradually into any exercise program. If you are thinking of starting an exercise program or increasing its intensity, you probably should check with your doctor. Intense exercise can kill people with blocked coronary arteries. Training for older people uses the same principles as those used by younger ones. You train intensely three days a week, and go slowly on the other four days. We average close to 20 miles per hour on our 25-mile rides on Tuesdays, Thursdays and Saturdays and only 10-12 miles per hour on our four recovery days.

As you age, you lose muscle fibers and strength. However, if you train intensely, you can maintain the size and number of mitochondria in muscles that use oxygen to convert food to energy, which helps you to keep your ability to move fast over long distances.


Dear Dr. Mirkin: Should a person with diverticulosis avoid nuts, seeds, corn and popcorn?

No scientific data support this recommendation (Nutrition in Clinical Practice, March 2011). Diverticulosis means that the colon has multiple outpouchings. The theory is that small food particles such as seeds might get caught in the outpouchings, but no one has shown that this actually happens. Furthermore, avoiding insoluble fiber found in all parts of plants is likely to increase risk for diverticulosis.

When solid food reaches the stomach, the pyloric sphincter closes and food is allowed to pass into the intestines only after it is converted to a liquid soup. It remains a liquid soup until it reaches the colon where fluid is rapidly absorbed to form solid material. Fiber is found in all foods from plants. It is composed of sugar molecules bound together so tightly that humans lack the enzymes necessary to separate out individual sugar molecules. Only single sugar molecules can be absorbed into the bloodstream. Thus fiber cannot be absorbed so it passes to the colon in the liquid soup.

The fiber holds water in the colon and helps keep the stool from becoming so hard that it blocks the passage of gas formed in the colon. Pressure increases behind the hard stool, swelling the colon to cause outpouchings called diverticula. Seeds, nuts and other plant materials help to keep stool soft and prevent diverticula from forming. On the other hand, refined flour that has had the fiber removed cannot hold much water, so it causes hard stool that is more likely to obstruct the passage of gas and increase the chance that outpouchings will form in the colon.


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Dear Dr. Mirkin: How does overweight cause diabetes, heart attacks, strokes, cancers and so forth?

Full fat cells and muscle cells with fat in them cause insulin resistance. Before insulin can do its job of driving sugar from the bloodstream into cells, it must first attach on specific hooks on all cell membranes called insulin receptors. However, when muscle and fat cells fill up with fat, their insulin receptors are blocked so that they cannot respond to insulin (Diabetes, May 1999). Blocked insulin receptors prevent sugar from entering cells, so blood sugar levels rise. A high rise in blood sugar causes sugar to stick to the outer surface of cell membranes. Once stuck on a cell membrane, sugar can never get off and is eventually converted to sorbitol which destroys the cell to cause all the side effects of diabetes: blindness, deafness, heart attacks, strokes, nerve damage, impotence, kidney failure and amputations.

As blood sugar levels rise, a person becomes diabetic. Diabetes is associated with increased risk for cancers of the breast, colon, rectum, liver, pancreas, bladder, stomach and uterus. Having diabetes is associated with an 11 percent increased risk of dying from cancer among women and a 17 percent increased risk of cancer death among men (American Association of Cancer Research, 102nd Annual Meeting, Abstract Number 947, April 3, 2011).


April 10th, 2011
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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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