Swimmers have a tendency to drop the elbow in backstroke. That is, they let the elbow lead the hand. This should be avoided, as it decreases stroke efficiency.

有些人在有仰泳时有沉肘的倾向，就是他们用肘部来带动手的动作。这个动作应该避免，因为这个动作可能会降低划水效率。

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A key to improving one's technique and stroke efficiency is to improve hip rotation.

提高游泳技术和划水效率的关键是提高转髋的能力。

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A key to improving one 's technique and stroke efficiency is to improve hip rotation.

提高游泳技术和划水效率的关键是提高转髋的能力。

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So when I got my custom bike, I told Seven Cycles this and they built in an oversized seat tube to add rigidity for my standing pedal stroke, an efficiency increase.

FORBES: Why You Need a Custom Road Bike