What’s the cause of a muscle spasm?

Muscle spasms are caused by a lack of oxygen or blood flow to the muscle, which can be caused by trauma or overuse.
 
Transcript: "Hi, this is Blair Green and the question I was asked is what is the cause of a muscle spasm? So what a muscle spasm is, it is a knot in the muscle. It's an area where the muscle tissue remains contracted. And the reason that happens in a muscle is typically because of lack of oxygen or lack of blood flow to the muscle. And so the muscle stays contracted and can't relax. There's a couple different reasons why that can happen. Two that I like to mention are trauma and overuse. So when I say trauma, that can be anything from an acute injury to maybe repetitive strain, which is also known as overuse. But really, when you injure a muscle, the muscle protects itself by going into spasm so that the tissue can heal. Overuse, like I said, happens with repeated movements over time. And when that happens, the muscle can get tired and blood flow reduces."