Posterior flye.Sit on a balance ball with your feet together and your back straight at a 45-degree angle to your thighs.是什么意思_Posterior flye.Sit on a balance ball with your feet together and your back straight at a 45-degree angle to your thighs.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句