Even though muscle cramps are extremely common in competitive athletes, we really do not know what causes them. Nobody has shown consistent benefit from any of the most common treatments: multivitamin pills; mineral pills with calcium, zinc, magnesium, salt and/or potassium; massage or chiropractic manipulation; drinking large amounts of water; dietary manipulations; or bio-mechanical stretching and strengthening.

Known medical causes of muscle cramps are extremely rare in athletes. These include narrowed blood vessels, usually from atherosclerosis; compression of nerves, low thyroid function, or side effects of medications such as diuretics. Some cramps are caused by low mineral or fluid levels (The Japanese Journal of Clinical Pathology, November 2007). However, for the vast majority of people who suffer exercise-associated muscle cramps, blood levels of sodium, potassium, calcium and magnesium are normal. Research in athletes after they ran in 52-mile races showed that the runners who suffered cramps had the same level of dehydration and blood mineral levels as those who did not get muscle cramps. Cramping during exercise usually occurs in healthy people without any underlying disease or known cause.

I think that the most common cause of exercise- associated cramps is damage to the muscle itself. Before you get a cramp, you will probably feel that muscle pulling and tightening. If you slow down, the pulling lessens, but if you continue to push the pace, the muscle goes into a sustained cramp and you have to stop exercising to work the cramp out. Further evidence that muscle damage is the cause of the cramp is that the muscle often hurts for hours or days afterwards.

You may be able to prevent cramps by exercising more frequently but less intensely and for shorter periods of time, but most serious exercisers do not want to do this. There is some evidence that taking sugared drinks and foods during prolonged exercise helps maintain endurance and muscle integrity which helps prevent cramps. So take a source of sugar every 30 minutes or so during a vigorous workout, and back off if you feel a group of muscles pulling and tightening during exercise. Most exercisers just accept that occasional cramps will occur and cause no long-term harm.


Reports from drmirkin.com

Warm up your heart


In response to last week’s report on bone strength, reader Guy Thibault sent the following important comment: “Animal studies suggest that a given increase in bone mineral density following exercise training corresponds to a 10 times greater increase in bone strength.” Dr. Thibault is an exercise physiologist and research advisor to the Government of Quebec. He cites the following articles: Robling et al. (2002) ‘trained’ rats 3 times a week for 16 weeks. Bone mineral density and bone mineral mass increased 5.4 and 6.9%, but bone resistance had increased by 64%. Robling AG, DB Burr et CH Turner (2001) Recovery periods restore mechanosensitivity to dynamically loaded bone. J Exp Biol 204(Pt 19):3389-407. Turner CH et AG Robling (2003) Designing exercise regimens to increase bone strength. Exerc Sport Sci Rev 31:45-5. Turner CH et AG Robling (2005) Exercise for improving bone strength. Br J Sports Med 39:188-9.

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Dear Dr. Mirkin: I still have pain six months after pulling my Achilles tendon; is this normal?

The Achilles tendon (in the back of the lower leg) is particularly difficult to heal because you stress it every time you take a step. Mild exercise hastens healing, but too much force on the tendon prevents healing. If you had a partial tear, I would have started you on a spinning bike with no resistance, soon after the injury (probably within a few days). Just move gently through your range of motion. As you get stronger, increase the resistance. You cannot use running, jogging or walking for exercise until the pain is completely gone. More on Achilles tendinitis


Dear Dr. Mirkin: Why would being overweight increase cancer risk?

There is no doubt that being overweight is associated with many types of cancers, including colon, breast, thyroid, kidney, uterus and gall bladder cancers. However, it remains to be proven whether obesity is the cause or a contributing factor. Researchers reviewed 141 studies conducted between 1966 and 2007 on the association between weight and cancer (Lancet, February 15, 2008). The subjects were followed for nine to 15 years. For men, a weight gain of 33 pounds increased risk for esophageal cancer by 52 percent, thyroid cancer by 33 percent, and colon and kidney cancers each by 24 percent. In women, a weight gain of 29 pounds increased risk for cancers of the uterus and gall bladder by nearly 60 percent, esophagus by 51 percent and kidney by 34 percent. Bone and blood cancer risk also increased with excess weight.

We do not know why obesity is associated with increased cancer risk, but it may be because full fat cells produce hormones that turn on your immunity to cause inflammation, which has been shown to increase cancer risk. I find it is fascinating that studies show almost the same cancers that are associated with obesity are also associated with eating meat: cancers of the esophagus, colon, kidney, rectum, pancreas, endometrium, gall bladder and breast.


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