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NCAA runner turned high school coach Hillary Kigar has an answer for all things training—especially when it comes to proper running form.
What does proper arm swing look like?
Before you do anything to change your arm swing…relax. Take a deep breath. Often poor running mechanics are a result of working too hard, forcing it and tightening up. If you watch any elite distance runner, you can see that they have a very smooth, steady, relaxed arm swing. The key is to push the elbow straight back—rather than to the side—so that it swings forward like a pendulum. The most efficient movement is that which propels you forward in the direction you are going. Any lateral motion such as arms crossing in front of your chest or not moving at all (and essentially acting as deadweight) will disrupt your efficiency and slow you down.