I think most Buddhist traditions agree that while meditating, you should concentrate on your breathing, and note when/if your mind starts to wander. So if you have a spasm, you don't have to deny it or feel like a failure, but you recognize that it's happening, but also maintain your focus elsewhere. You're focusing on your meditation, and whatever happens with your body goes on in spite of that because you're human, but doesn't have to detract from your focus. You can tell your focus where to direct itself.
I know it's popular to say meditation can help with spasms and restlessness. I think people say that because they find it teaches them to be at peace doing nothing, and that they can choose not to worry or think negative (or any) thoughts. Personally, I'm not at that level, and I tend to become more worried when I'm not doing anything. Perhaps for that reason, I don't schedule very long meditation sessions. If I say I'll meditate only for 15 minutes, then I can believe that it's okay to meditate and give the meditation my full attention for that time. If I schedule a longer time, then I have trouble really believing that it's a good use of my time, and I get fidgety.