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[Typing this while my right hand is cramping.] Cramps can be very common if you don't warm up properly before exercising. I'm sure I don't need to explain it, but a cramp can be unbelievably painful. Apart from exercise, cramps can be caused by overusing a muscle, dehydration, or simply just by not moving for an extended period of time. Cramps are generally sudden involuntary muscle contractions that cause significant pain. The sudden pain can also trigger symptoms similar to paralysis.

If it's a cramp caused by overusing a muscle, continuing to use that same muscle will double, triple or even quadruple the pain you are feeling. You really have to consider the situation if you plan on powering through. The area around my metacarpophalangeal thumb joint is currently swollen red and hurts whenever I move it. I had to draw 3 drawings for tomorrow where each one took over 3 hours to complete.

It doesn't matter what kind intense activity you plan on doing, you should probably stretch the muscles that will be involved ahead of time. Otherwise you run the risk of painful cramps or muscle soreness on the following day.