On the other end, some runners hold their arms too high when fatigued or when sprinting. Fatigue can cause tenseness in the shoulders and facial muscles which can result in the runner tightening the arms and bringing them up too high.
It's important to stay relaxed in the shoulders, hands, eyes, forehead and arms, and keep the elbow at the 90-degree position.
Thumb and Index Finger
How the hands are held while running is a small point but nonetheless important. I like my runners to cup the middle, ring, and small fingers loosely against the palm of the hand. The tip of the thumb should be placed under the index finger at the middle joint. This helps maintain proper arm position, balance and relaxation.
Thumb to Chest
Some runners flap their hands and arms, often to compensate for improper techniques or underlying movement and stability limiters.
With your thumb and index finger in the correct position, bring the top side of your thumb to the middle of your chest (on the appropriate side) during the forward arm swing.
You don't necessarily have to touch your chest, but the motion of each arm should be directed toward the middle of the pectoral (chest) area on that side. Many runners don't seem to know what to do with their arms, and this technique provides a target for where to direct the arms during the upswing.
With the hands gently cupped and the proper thumb and index finger positioning, the wrist should be loose but controlled.
Former Humboldt State University track coach Jim Hunt referred to this motion as "tapping". He asks the runner to visualize holding a tapping (tack) hammer in each hand. The hammer is held ever so gently between the thumb and index finger and flexes upward and downward toward and away from the chest.
Good running form can be learned, it's just a matter of learning how to move efficiently and creating new habits.
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