Is it necessary to be completely still during body scan?

I've been practising vipassana for some time. Now, I'd like to try body scan, but one issue isn't clear for me. Books or articles about sitting meditation, I've read, say that it's good to sit completely still during practise. Does the same implay to body scan? Should I lie entirely still during body scan or can I move my hand, for example, when I feel such a need? Thanks for your answers.