Richard L. Bruno is chairperson of the International Post-Polio Task Force and director of The Post-Polio Institute at Englewood Hospital and Medical Center. Please e-mail questions directly to him at ppsforum@newmobility.com.

Note: This column is for information purposes only and is not intended as a substitute for professional medical advice.

Q: If the accepted theory of post-polio muscle weakness is that our motor neurons are dying, why do I improve with rest after having a period of severe weakness when I overdo? Even though I can become completely lame, the loss is temporary if I rest up for a day or a week.

A: You're describing a symptom that PPS researchers have totally ignored: "transient weakness." We call it "New Year's Syndrome." Polio survivors complain that their muscles become significantly weaker in late December, more than likely because of too much Christmas shopping, but strength returns in January after they rest.

But something dangerous is happening to cause the transient weakness of "New Year's Syndrome." Remember that the poliovirus killed off at least 50 percent of your motor neurons. The neurons that weren't killed were damaged by the poliovirus but were able to sprout--send out extra "telephone lines"--to talk to the muscle fibers that were orphaned when their motor neurons died. After polio you were left with less than half of your motor neurons-neurons that not only are oversprouted, but also have cell bodies that are smaller than normal, have damaged protein-making "factories," and have been severely overworked for the past 50 years.

When you experience transient weakness, we think you have overloaded your neurons' protein-making factories and drained their reserves. After you rest, the neurons' protein supply increases and you are able to use your muscles again. But every time you drain your motor neurons, we think you are doing damage that eventually causes permanent weakness as the drained neurons die. Think of what would happen to your car battery if you left the headlights on every night. You get up the first morning and your battery is flat. You jump-start the battery and drive off. The next night you leave the lights on, jump-start the battery again, and drive away. But after about a week the battery will no longer take a charge and you won't be driving anywhere!

Canadian PPS researcher Alan McComas found that polio survivors who are getting weaker over time lose 7 percent of their motor neurons per year. That's 7 percent on top of the 50 percent they have already lost! Prevent transient weakness--and possibly permanent weakness--by resting before your muscles become weak, let alone completely lame. Remember: You can replace your car's battery, but you can't replace your motor neurons.

Q: I have a clogged artery in my heart and my doctor told me to walk around the high school track. I walked every night after dinner and worked my way up to 10 times around. A month later I could only do five times, then two, and now I can't even walk to the track. My doctor is mad at me, but I just can't walk the track anymore. What can I do for my heart?

A: Your body has two conflicting needs: One important muscle needs exercise and a bunch of other muscles need rest. There are only a few studies of heart exercise in polio survivors. One was aggressive, where polio survivors did five minutes of bicycle exercise followed by a 60-minute exercise class twice a week for five months. This study found that polio survivors' legs became four percent weaker while their maximum heart rate during exercise (an indicator of heart muscle strength) increased by 12 beats per minute. This is exactly the tradeoff you describe: The heart muscle gets stronger while the leg muscles get weaker.

Other studies of heart exercise in polio survivors were not aggressive. In fact, the amount of exercise was reduced if polio survivors reported discomfort, pain or fatigue. In these studies, polio survivors peddled an exercise bicycle, either with their legs or with their arms, doing "interval training"-peddling for two minutes and then resting for one minute. In this way, with fatigue and pain as their guides, polio survivors peddled for 20 minutes, increasing their peddling from two to four minutes per interval by the end of the study.

Those who used the leg bicycle increased their maximum heart rate by five beats per minute, while those who used the arm bicycle increased it by 11 beats per minute. Since most polio survivors' legs are weaker than their arms, non-fatiguing arm bicycle exercise could be not only a more effective heart exercise, but also possible to do, as long as arms don't get weaker or shoulders more painful as a result of the exercise.