By working to improve your form, you can adapt to stress and avoid injury. At the same time, you will become more efficient and have a better chance of achieving your goals.
The Shoulders and Upper Arms
Keep them relaxed. Though the shoulders and upper arms primarily provide balance at relatively slow speeds, they can assist the leg muscles more as you run faster and climb hills. Proper movement of the arms and shoulders prevents your trunk from rotating too much from side to side, which wastes energy.
Let your arms swing loosely. Don't hunch forward, and don't pull your shoulders back and thrust your chest out. The place for shoulders is directly above the hips. Unnecessarily tensed muscles always decrease your efficiency.
The Lower Arms
Match the armswing to your running speed. Vary your arm action with your speed, becoming much more vigorous as you run faster. Keep your elbows close to your body to minimize the tendency for the hands and lower arms to swing across the chest.
At most speeds, your elbows should remain flexed at about 90 degrees through the full range of the armswing. When you sprint at the end of a race, however, let your elbows unlock beyond 90 degrees on the backswing and close to perhaps 30 degrees on the forward swing. This will give you power and fluidity.
Keep them loose but not limp. Even in the final moments of a race, your wrists should be fairly loose, your fingers should be slightly bent, and your thumbs should not be sticking up like spikes.
Keep it poised above the shoulders and hips. Except when you are making a desperate dip at a finish-line tape, your head should be poised well above your shoulders.
The head is a very heavy piece of anatomy. If you don't hold it properly, you are likely to develop problems. When your head tilts too far back, it places unnecessary strain on the neck muscles. If it rests too far forward, it can restrict the airways and make breathing difficult.
Part two: Analyze your lower-body form