Ok if you are injured you need to rest - training on injuries is a big no no and will only come back to bite you in the ass at a later stage or cause you to be out of commission for a longer period of time. Stiff or tight muscles should not be confused with an injury, sometimes a good stretch can sort this out and other times over stretching can be the cause of your problem. Pushing yourself in a race and having sore muscles is a good thing - that is why it is called a race, if you are not going to push yourself to the max you may as well go for a training session. Try to train for a longer distance than what you are going to race eg Race distance is 100km's train for a distance of 120km's - simply this allows your body to adapt and leaves you some gas in reserve. Also consider that your body is a actually very clever and it learns to do more with less. So doing the same training regime over and over will make your body more efficient which in essence means you will become less fit. You need to confuse the issue, you can do the same amount of training in time and distance but vary your routes - even do them the other way around just to get your body out of the routine. Hope this helps - oh and rest, don't run when you can walk, don't walk when you can sit and don't sit when you can lie down!!
