Running should be a fluid and natural act that if over-analyzed can inhibit one's natural ability. We can, however, give you some tips on how to get the most out of your running form.
Head - The head should remain over its base of support - the neck, with the chin neither pointing up or down. Allowing the head to ride forward puts undue strain on the muscles of the upper back.
Shoulders - The shoulders should assume a neutral posture - neither rounded forward or forcefully arched backward. Rounding the shoulders forward is the most common fault in everyday posture as well as with running. This is usually associated with tightness of the pectoral muscles of the chest. Another problem occurs when the shoulder girdle starts to rise with fatigue or increased effort. This position not only wastes energy, but can adversely affect breathing also.
Arms - Throughout the arm swing, the elbows should stay at roughly a 90-degree bend. The wrists stay straight and the hands remain loosely cupped. Though the arms swing should be free of tension, allowing the hands to cross the midline of the body is excessive.
Trunk and Pelvis - Like the head, the trunk should remain over its base of support - the pelvis. A common problem with fatigue is allowing the trunk to get in front of the legs and pelvis. This forces the lower back muscles to spend too much energy resisting further trunk collapse to the front.
Legs - For distance running, much of the power comes from below the knee. Energy is wasted as the knees come higher and the big muscles around the hips and thighs get involved. Practice getting a strong push-off from the ankle of the back leg. This helps to naturally lengthen the stride. Lengthening the stride by reaching forward with the front leg will be counterproductive.
Feet - For most people, the feet should be pointing directly forward while running. With fatigue and certain muscle imbalances, the legs and feet will start to rotate outward. This hinders performance and may create abnormal stresses that cause injury.