The two primary modes of fulfilling the mitzvot of Torah study and prayer are speech and thought.
The halakha states that mere thought is not tantamount to speech, such that if, for example, one is capable of speaking words of Torah yet merely thinks of them in his mind, he has not fulfilled the mitzva of Torah study. Halakha also maintains that even the movement of one’s lips is regarded as an action.
Thus, even these thought-and speech-related mitzvot require a physical action – either being actually uttered, or at the very least, mouthed.
It is thus clear that a person cannot fulfill a mitzva, even one which does not entail a concrete action -such as Torah study or prayer – without some degree of bodily movement.
Rabbi Adin Steinsaltz