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Why do muscles cramp and how can I stop it from happening?

You jump to block your opponent's shot, and while you're midair you realize that the twitch which got you in the air never ended. Your calf muscle is still rock solid with your toes pointing to the ground, but it's not because of a signal your brain is sending. It's out of your control. Now you need to land, but with your calf muscle locked beyond your control you shift your center of gravity so that you might land on your hands because if you land on your ankle you think it will break given the limited range of motion it's experiencing. You land hard on your hands and try to slide to break your fall. The game stops and everyone asks if you're okay. Your toes are still pointed away from you and you can't get them to relax. You grimace and tell them, "It's no big deal it's just that my calves are locked up. It's just a cramp but I can't make it stop." You roll over on your back, hobble off the basketball court, and meekly ask for a sub because it's the worst when you wait an hour to play a game of pick-up ball and one of your teammates can't hold their own and thus your team can't hold the court since the losing team will be off.

This was my story a few nights ago at the CU rec center. My calf muscles (gastrocnemius) started cramping in an unusual way. It’s normal for my muscles to lock up after playing for a couple hours, but this started happening after the second game, and almost every step that I took in which I landed on the balls of my feet created these little mini cramps. Not cool. Also, not normal. So I figured I ought explore the phenomenon of muscle cramping. Let’s start with muscle fiber structure. (Note: I do not own the rights to these images. They are not my work. I am not trying to make any money off of them. I am using them for educational purposes only. I'll take them down upon the owner's request.)

The process of muscle contraction begins when your brain sends a signal that tells your muscle to contract which moves through the motor neuron to the sarcolemma (the outer lining of your muscle fibers). The sarcolemma sends a signal via the t-tubules to the sarcoplasmic reticulum (SR a specialized version of the endoplasmic reticulum) which releases massive amounts of calcium ions. Calcium ions (Ca2+) bind to troponin (an inhibitor on individual actin filaments) changing its shape which then allows the myosin heads to bind to the actin filaments and pull them toward the center of the sarcomere with ATP providing the energy for the process. When this happens across many muscle cells, the muscle contracts.

This animation really helped me get a better picture of the situation.

In order to have the muscle relax again, ATP needs to bind to the myosin head, the calcium ions need to be removed via active transport, and the binding sites on the actin filament need to be covered again. The muscle cramps when it cannot let go of the actin filament.

Based on this understanding, it seems the most likely cause for my excessive muscle cramps stems from a lack of ATP (Adenosine TriPhosphate which is produced in cellular respiration). There are so many points in this system that require it, but most importantly in terms of cramping is when ATP is required to bind to the myosin head in order to let go of the actin filament. ATP is also required to pump the calcium ions back into the SR.

So how can I make sure that I have a better reserve of ATP? Stay hydrated and eat more. The largest source of ATP is from the process of cellular respiration. Cellular respiration relies on having enough water and glucose. Water is also required to maintain the correct ion balance inside and outside the cell.

Meat is a natural source of creatine which your body can use to make creatine-phosphate which can quickly be converted to ATP. But eating meat comes with a high cost to the environment. So the vegetarian option would be to eat more peanuts, walnuts, coconuts, chickpeas, soybeans and oats which have the amino acids arginine, glycine and methionine needed to build creatine. (Creatine supplements have not been proven to build muscle, but I'm sort of tempted to try it only to see if it helps prevent cramping.)

I did eat a good amount of beans and potatoes about an hour before I played basketball. I know it takes time to break down complex carbohydrates into glucose and proteins into amino acids for use by the body. So maybe it wasn’t enough time. Prior to the beans and potatoes my food intake was rather minimal. I had a few granola bars and some cake at lunch. For breakfast I had frosted mini-wheats.

Maybe it had to do with the fact that I was on my feet all day prior to playing basketball. Could also be that I haven’t really been exercising as regularly since tennis and ultimate frisbee are out of season currently. Lack of sleep could play a role as well. I went to bed a little after midnight and woke up around 5:15. Could sleep be a time in which ATP reserves are restored? That might be another post.


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