Gē yuē. Shǒuxīn kōng. Shǐ jiàn huó. Zú xīn kōng. Xíng bù jié. Dǐng xīn kōng. Shēn yǎn yī.
The song says
With palm empty, the sword is lively.
With the center of the foot empty, the footwork is nimble.
With the topknot empty, the entire body is one.
The topknot refers to a daoist hairstyle where long hair is wound up into a knot that sits atop the apex of the head, held in place by a peg. “Keeping the topknot empty” means not hanging the head, inclining the body forward, nor titling the head back, so that it is pulling the body backward off balance.
Fundamentals of the Wudang Sword Method - Selected Translations with Commentary from a Manual of Chinese Swordsmanship