There are general rules for injury prevention and it is vital that these are adhered to if loss of fitness and form are to be avoided as a result of disruption of one's training due to contracting an injury.
It is normal for ambitious runners to increase the quality and/or quantity of their training in a quest for continuing progress.
It is important as a runner to consider the longevity of your career in relation to injury and the surface you run on.
Most endurance runners undertake a pre-competitive and training session workout with a warm up routine, on the understanding that the main activity will benefit from it.
The bane of a runner's life, a stitch or ache in the side inevitably compromises performance, be it in training or in a race.
The worst example of muscle stifness I have experienced has always been after fell races with a significant amount of steep downhill sections.