The master dall’Agocchie famously wrote about about the five tempi for attack. The last concerns movement of the foot,
The fifth and last, when the enemy is fixed in guard, and he raises or moves his forward foot in order to change pace or approach you, while he raises his foot, that’s a tempo for attacking him, because he can’t harm you as a result of being unsettled.
This is a common belief among later masters. Fabris himself brings up the issue multiple times,
As I have already said, if you are stationary with both feet on the ground, you cannot move them without performing two tempi: one to life the foot, the other to place it on the ground.
If we limit ourselves to just these two passages, it seems like one should fence timidly. Rather than being aggressive, you wait for your opponent to approach and offer a tempo. But that’s not always an option. So many masters, modern and historic, would have you limit the time you are in danger by taking small “advancing steps”. This is when you move the front foot first, by a foot-length or two, then place it while moving the rear foot forward by the same amount.
But to Fabris this is even worse because you are four tempi with each advance. Furthermore, your weight is alternately being shifted forward or back depending on which foot you wish to move next.
So rather than these stuttering advancing steps, Fabris would prefer that you stay continuously in motion. Allow me to quote the above passage in context,
As a first consideration, a person who moves from a stationary position will always be slower (by virtue of his weight) than one who is already moving. As I have already said, if you are stationary with both feet on the ground, you cannot move them without performing two tempi: one to life the foot, the other to place it on the ground.
On the other hand, someone in motion will always have one foot in the air and the other firmly on the ground. In this lies the great advantage of having already completed what the opponent has yet to begin.
To stay in motion you need to become proficient with “passing” or “walking” steps. As in everyday walking, your center of mass continues to move in one direction as your weight is sifted from one foot to the other and back. Think of it not as series of alternating “move foot-shift weight” pairs but rather “my weight is on whatever foot happens to be under me at the moment”. Fabris writes,
If you wish to approach your opponent, you should start by moving your feet at an ordinary step, as if you were walking – only quicker and smaller strides. This step should not be widened until the point of your sword reaches the opponent.
Though Fabris doesn’t fully explain this concept of continuous motion until Book 2, his first mention of it can be found in text for plate 2, which shows the properly formed Prima.