During marathon training, especially if it is your first, you are pushing your body to do something it's never done before. You'll be running distances you've never run before, for lengths of time you've never run before – and that will most certainly cause aches and pains at some point. You wouldn't be human if it didn't. The most important thing is to be honest with yourself, and to learn to listen to your body, making a distinction between pain from DOMS [delayed onset muscle soreness], and pain from a niggle or injury that may get worse if you push it too far. This is a lot easier to say than to do, but if you aren't sure then on the whole it's usually best to err on the side of caution. An extra rest day here and there may be all you need to recharge your batteries a little, or to let a sore muscle ease, but do take any actual injuries seriously – and to a physio if necessary.
