Why do many tennis players crouch-then-uncrouch before receiving a serve?

Question

I’ve been watching quite a lot of tennis this year, and I’ve been noticing a tendency among many professional tennis players—particularly noticeable in women players, for some reason—to crouch down fairly low when waiting for their opponent to serve, and then straighten halfway back up just before the opponent actually serves.

This FTP Tennis page describes crouching down too low as a common ready-position mistake, borne out of people observing this precise crouch, but missing the player straightening back up.

For reference, here are two pictures of Novak Ðoković in the two positions in question, taken from the same page:

Crouching:

Straightening:

Given that the player usually ends up in a ready position which is almost identical to the position they were in before they crouched down, I can’t help but wonder why they do the initial low crouch at all.

Why not just go directly into the final ready position? Wouldn’t that be easier?

Answer 1

Part of why I do it, as a reasonably high standard player myself, is that it gets the weight moving forward.

If you're just stood flatfooted waiting for the serve, when you then try to move you have to get your weight moving. You want to be pushing off forward after the splitstep (as one should hit shots while moving forward), so doing the crouch then moving up and forward helps with this.

You see some players start with their feet wide apart and one quite a distance in front of the other (I often do this myself). As their opponent starts to serve, the player pulls the back foot forward, getting the weight moving forward, and lands a splitstep as the serve is hit: they are then ready to move forward to be hitting a better shot, and side-to-side with the splitstep.

Answer 2

It's called a "split step." By crouching sort of down and the jumping up, the player ignites a stored elastic energy. By timing their final short hop so they land just as the server makes contact with the ball and evenly balancing the takeoff and landing of their short hop, allows them to move either direction or stay where they are to react to the server's ball. See science of Countermovement Jumps for biomechanics, etc, but in a nutshell, it has to do with eccentric, concentric muscles and the players' fast twitch fibers. Every millisecond counts in responding and moving to the correct position to return the serve.

Answer 3

According to Frans Bosch who is a renowned performance coach from Netherlands, this so-called "option posture" tenses up the muscles in the front side of the body by pushing one's hips forward (which is why it looks like one's uncrouching) which is important when initiating any sort of change of direction which in this case is starting a movement from a standstill position.