How are you feeling right now? Sometimes being the best runner or walker means knowing when not to train.
This is the cold and flu season, you've just come out of the holiday season, where you had a round of parties, concerts and everything else from dusk 'til dawn, as well as trying to get your training in.
If your body is tired, listen to it. Take the opportunity to rest when you need to, because rest is a very, very important component of your training and it only gets more important as the mileages get longer.