Rashi, Menachem: My ways, lying and dwelling - You surrounded them with a wall. I cannot do anything without Your knowledge. "Zerisa" is like "Zer Zahav" (Shemos 25:24).

Rashi citing Nidah 31a: This refers to a drop of semen; the fetus is formed from the choicest part of it. "Zerisa" is an expression of Zoreh (winnowing), to select the waste from grain.

Radak: My going during the day, and lying ¹ on a bed at night [You knew].

Radak citing ha'Kuzari (3:11): I have a desire, e.g. to rise, and I do not think which limbs must do what in order to carry this out - they are arranged with Chachmah to do so automatically.

Malbim (2-3): This refers to natural actions, such as eating and Bi'ah. You surround them like a Zer (crown), and know all of them.

Rashi: You taught.

Radak: You accustomed. This is like "ha'Hasken Hiskanti" (Bamidbar 22:30). You know all my ways, like one who is used to a matter knows it.

Radak citing his father: In back and in front, in all four directions, above and below, right and left, You scattered - this is like "Ezareh l'Chol Ru'ach" (Yechezkel 12:14). You fixed and helped my matters from all sides.

Radak citing Ibn Ezra: The five senses. He gave to each limb its sense, and accustomed it to it. And so each limb, what one limb does, another limb does not do.

Malbim: Actions that a person does by habit - You taught and accustomed me to them.