Swimming improves heart action, aids blood circulation, and helps develop firm muscles.

游泳改善你的心脏起搏，增加血液的循环能力，并且有助于肌肉成型。

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This treatment helps tone the body, firm up muscles and tighten the skin.

这种治疗可以帮助保持体态，使肌肉变结实、皮肤紧致。

《柯林斯英汉双解大词典》

Firm the muscles of your legs into your bones on all sides, both in your lower legs and in your thighs.

加强你腿部肌肉从所有方向包裹骨骼，腿低的位置和大腿都要收紧。

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Moscow's flexing of its muscles in the energy sector - which saw state-owned firm Gazprom temporarily cut off gas supplies to neighbouring Ukraine - as well as new rules for the foreign ownership of Russian companies and export tax rises, all have implications for BP.

BBC: Analysis

In principle, muscles with shorter fibres ought to exert less downward force, making those who have them less firm on their feet.

ECONOMIST: Anatomy and behaviour