Ask Linda

by Linda Wobeskya, M.S., P.T., GBPPA Member

This column originally appeared in the Winter, 2001 issue of TRIUMPH.

Dear Linda,
I can’t seem to do as much as I used to be able to do. I used to walk about a mile every day and now I get very tired after only about half a mile. I usually push myself to finish my walk anyway because I know exercise is important. What exercises can I do to get stronger? Getting Tired in Tewksbury

Dear Getting Tired,
This question falls into the category of frequently asked questions! Many polio survivors report their daily battles with tired muscles and decreasing ability to do the things they want. The most successful approach to solving a problem is to first understand its cause. Today’s column will explain the causes of muscle fatigue. The next newsletter column will present a variety of strategies for coping with muscle fatigue.

The cause of muscle fatigue is related to your recovery from polio. The poliovirus damaged or destroyed the nerve cells (motor neurons) in your spinal cord, which transmit the messages from your brain to your muscles. If you want to wiggle your big toe, your brain sends the message down your spinal cord to motor neurons, which then conduct the message down your leg to stimulate the muscles that wiggle your big toe. Each motor neuron is connected to specific muscle cells in a particular muscle. The poliovirus damaged or destroyed these motor neurons in your spinal cord, which cut off communication between your brain and your muscles. The specific muscle cells that depended on that particular motor neuron were orphaned, or lost their communication line to the brain. The motor neurons that were spared during the polio attack sprouted extra branches and reconnected as many of these orphaned muscle cells as possible. This is one of the ways you recovered your strength. However, the result was one motor neuron now controlled as many as five times more muscle cells than it was originally designed for. For example, if that particular motor neuron originally controlled 200 muscle cells, it might now control over 1000 muscle cells. This means it sprouted over 800 extra branches. As the years go by, the motor neurons become less and less able to support all these extra branches. As a result, these branches begin to slowly die off.

Here is an analogy. Imagine that you added 3-4 new rooms to your home during the years when heating oil was plentiful and inexpensive. Then there was a crisis in the Middle East and fuel prices skyrocketed. What would you do? You would close the doors to those new rooms. When the motor neurons “close the doors” to these extra branches, the branches die off. The muscle cells again lose their communication line with the brain. When the brain sends a message down to that muscle, fewer muscle cells are able to respond, because fewer muscle cells actually received the message. What you experience is new muscle weakness.

There is another important point to consider. Your muscles can not differentiate between activities you consider “exercise” and regular daily activities. The quadriceps muscle in your thigh works when you use the stairs in your home and when you exercise it at the health club. Your motor neurons and muscle cells don’t know the difference. So everything you do during the day is experienced as exercise by your muscles!

Let’s take a moment now to reconsider your situation. You used to walk for a mile and now you feel quite tired after half a mile. Your mind says, “A half-mile should not make me feel tired. It’s not that far.” The truth is, it doesn’t matter whether you think a half-mile, or even a half block is very far. Your muscles are telling you that it is more than they can do. When you push yourself to walk the mile, you are ignoring this message. If you ignore the message, you risk serious and perhaps permanent damage. When you continue to exercise when your muscles feel tired, you are taxing your already overworked motor neurons. You may be helping those extra branches to die off. Is this something you really want to do?

When you first had polio, exercise was the means to increased strength and function. So it makes sense to think that exercise will help now. However, your original weakness was caused by the polio infection. The cause of your current problem is described above. Different causes require different treatments. So you might guess my answer to your question regarding which exercises you need to add to your day. More exercise will not help you to get stronger. In fact, more exercise could cause you to lose strength permanently. “But,” you say, “I have to do something!” I most heartily agree. There are many things you can do to feel stronger and to feel better overall. I will discuss these in the next column. Stay tuned!

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