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The objective of underwater finish is to make quick recovery.

When you finish your stroke,  you normally push the water near the surface. Since your hand is pushed (far away from your elbow), it is difficult to relax your elbow at the recovery phase.

I recommend to finish underwater, which means you snap your hand in the water and use the resistance to move your elbow forward like bouncing.

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TI coach Shinji Takeuchi teaches "graceful freestyle" in Bay Area

Visit TI Swim West(tiswimwest.com) for detail