Monday, December 28, 2009

The Hygiene Hypothesis

A study on mice may explain why it's not so bad to get lots of infections when you are young. Many studies show that children raised on farms are less likely to develop allergies than those raised in cities. If your immune cells and proteins do not get a lot of practice and learn how to recognize bacteria and viruses, they may attack pollen, mold, dust and other particles that are not bacteria to cause allergies that show up as skin rashes, nasal and lung obstruction and irritation.

Researchers at The University of Marburg in Germany worked with a line of mice that had been genetically programmed to develop asthma. They sprayed Acinetobacter lwoffii, a type of bacteria found in farmyards. into the noses of pregnant mice, and this prevented their newborns from developing asthma (The Journal of Experimental Medicine, December 2009).

Asthma means intermittent obstruction of the bronchial tubes that carry air to and from the lungs. It is caused by the body's immune cells and antibodies attacking something unknown in the lungs to cause the bronchial tubes to fill with mucous, the inner linings of the bronchial tubes to swell, and the muscles surrounding the bronchial tubes to constrict and block the airways.

When a germ gets into your body, your immune cells and antibodies recognize that the germ has surface proteins that are different from your own surface proteins, and they attack it to try to kill it. This causes swelling and irritation. The Hygiene Hypothesis is that exposure to lots of germs when you are young gives your immunity practice in attacking germs so it will not attack your own body tissues or non-germs such as mold, dust or pollen.

This study shows that exposing a pregnant animal to germs can prevent allergies in their offspring. However, it is unreasonable and probably dangerous to recommend exposing pregnant women to infections. We await further studies to see if extreme cleanliness and protection from infections causes allergies.

Friday, December 18, 2009

Stress Fractures Caused by Weak Muscles and Over-Striding

One of the most common injuries in runners is a stress fracture of the lower leg (tibia) because running fast causes the foot to hit the ground with tremendous force that can shatter bones. A study from the University of Minnesota shows that women with stress fractures do not have weaker bones, they have smaller and weaker calf muscles (Medicine & Science in Sports & Exercise, December 2009). Another study from Iowa State University in Ames, in the same journal, shows that longer strides cause the greatest foot strike forces that increase bone fracture risk.

Strong muscles may help to prevent bones from breaking by absorbing more force from the foot hitting the ground during running. Most distance runners do not use weight machines to strengthen their leg muscles. They strengthen their calf muscles by running very fast no more often than three times a week.

In the Iowa study, reducing stride length by ten percent reduced force of the foot striking the ground and therefore reduced force on the tibia.

Shortening your stride will not slow you down. When your foot hits the ground, your Achilles tendon contracts to store up to 60 percent of your foot strike force. Then when you step off that foot, your Achilles tendon releases the stored energy to drive you forward. Over-striding deprives you of some of this stored energy. Since many runners take strides that are too long, shortening stride length usually allows them to increase cadence and will help to increase speed and endurance.

Tuesday, December 01, 2009

Why Sprinting Improves Endurance

Jens Bangsbo of the University of Copenhagen has shown that if you want to run, cycle or swim faster at any distance, you have to train at a pace that is almost as fast as you can move (Journal of Applied Physiology, November 2009). He asked competitive distance runners to reduce their mileage by 25 percent, and to run 8 to 12 30-second sprints 2-3 times a week, with some additional 0.6-0.8 mile sprints 1 or 2 times per week, for 6 to 9 weeks. The control group of runners continued their regular training program, and showed no improvement. The sprint group improved both their 3K (1.8 mile) and 10K (6 mile) race times by more than three percent (more than a minute in the 10-K race). Half of them ran their best times ever, even though many had been racing for more than five years.

Two years ago, Dr. Bangsbo did ground-breaking research supporting the leading theory that exhaustion of the sodium- potassium pump is the major cause of muscle fatigue during exercise (Acta Physiologica, November 2007). In this new study, he shows how sprint training improves a muscle's capacity to pump potassium back inside muscle cells during exercise, which helps all athletes run or cycle faster in competition, even in endurance events such as marathons and multi-day bicycle races.

A muscle can contract only if it has an electrical charge across the muscle cell membrane. This electrical charge comes mainly from having sodium primarily outside the cell and potassium primarily inside the cell. This higher concentration of sodium outside the cell and higher concentration of potassium inside the cell is maintained by sodium-potassium pumps in the cell membranes. The pumps get their energy from an enzyme called ATPase.

When the brain sends electrical signals along nerves leading to each muscle fiber, sodium moves rapidly into muscle cells followed by an equivalent movement of potassium out of the cells, causing the muscle fibers to contract. However, the sodium- potassium pump cannot pump potassium back into the cells as fast as the rapidly-contracting muscle cells move potassium out.

Dr. Bangsbo showed that during rapid contractions, muscle cells lose potassium so fast that there is a doubling of the potassium outside cells in less than a minute. The electrical charge between the inside and outside of muscle cells is reduced, and they contract with much less force until finally they cannot contract at all. During continuous contractions of muscles, the loss of force from a muscle contraction is directly proportional to the amount of potassium that goes outside the cells.

Over time, repeated muscle contractions themselves will markedly increase the ability of the sodium-potassium pump to pump potassium into cells. The greater the force on a muscle during training, the more effectively the potassium pump can pump potassium back into muscles, resulting in greater endurance for the athlete. So intense training is necessary for endurance, and any training strategy that increases the number of intense workouts will give the athlete greater endurance.

You can also increase the effectiveness of the sodium potassium pumps by being excited before a race (which increases adrenalin), and by eating before and during races (which raises insulin levels). Hormones known to strengthen the sodium- potassium pump, and therefore to increase endurance, include adrenalin, insulin, insulin-like growth factor I, calcitonins, amylin, thyroid, testosterone and cortisones.

How to apply this information to your training program:

You cannot gain maximum endurance just with continuous exercise. To improve your potassium-sodium pumps, you have to put maximum force on your muscles. This requires some form of interval training. (CAUTION: Intense exercise can kill a person with blocked arteries to the heart; check with your doctor before increasing the intensity of your program.)

Intervals are classified as short intervals that take fewer than 30 seconds and do not generate significant amounts of lactic acid; and long intervals that take more than two minutes and generate large amounts of lactic acid. The longest you can exercise with maximal force on muscles is about 30 seconds. All competitive athletes should do some sort of 30-second interval. Nobody knows how often you have to do this, but most runners and cyclists do short intervals once or twice a seek. You probably should do long intervals also. However, applying near-maximal force on muscles for more than 30 seconds causes considerable muscle damage, so you have to allow muscles to recover by doing slow training for one or two days afterwards.

Since short intervals do not accumulate much lactic acid, you can do a large number of repetitions during a single workout. Long intervals cause a tremendous amount of muscle damage, so you can only do a few long intervals during a workout. A sound endurance program should include a lot of slow miles, one or two workouts with many short intervals, and probably at least one workout that includes a few long intervals each week.
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