I have discovered that when runners have problems, they tend to occur in three areas: Posture, stride and bounce. And the problems tend to be specific to the individual, occurring in specific areas. Fatigue brings on most of the problems relating to form. A slight over stride (even a fraction of an inch), can increase tightness and muscle weakness at the end of a run. As a tired body “wobbles”, other muscle groups try to keep the body on course, but are not designed for this, and can be pushed into soreness or injury. If you feel relaxed and running is easy even at the end of a run – you’re probably running correctly.