I think playing fast is not a matter of muscle, rather it is a matter of developing the neural pathways – which we train by practicing. So either way we can’t get around putting in the time.
In any case the smoother (meaning familiar) those neural pathways become over time, the faster the electrons can send the message to the fingers – or more likely we learn to anticipate the next movement!
Yes, I think if we wait to think the next movement-instruction, we are already too slow. I think that from practice comes the ability to flick off multiple instructions down that neural path – rather than sending one after another.
Of course I don’t know whether there is any research, on musicians or athletes for example, that could support my theory…