• 1. keep back straight: 保持背部挺直
• 2. Keep Your Back Straight: 保持背部挺直

• 1.Keep back straight and bend knees.
  背要直，只弯两膝。
  dict.yoduao.com
• 2.Lean on the ball as shown, keep the back flat or maintain its natural curve, with the legs straight.
  身体俯卧于球体之上，动作如图所示。背部保持正直或保持自然弯曲状态，腿部伸直。
  dict.yoduao.com
• 3.Keep your front shin vertical, back knee straight, back heel lifted, and chest lifted.
  保持前面小腿垂直地板，后膝伸直，后脚跟离地，胸腔上展。
  dict.yoduao.com

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