Question About Second Serve

[kazou1388]

I commonly like to watch tennis videos of pros in court level view. After watching videos of Andy Murray play I wonder why he flails his left arm up after serving (second serve). He doesn't always do this. Is it for balancing purposes or something else?

 

[heninfan99]

Kyrgios also uses this finish.

 

[WildVolley]

I commonly like to watch tennis videos of pros in court level view. After watching videos of Andy Murray play I wonder why he flails his left arm up after serving (second serve). He doesn't always do this. Is it for balancing purposes or something else?

It is for balance and designed to stop shoulder rotation more rapidly by bringing the weight of the arm to the rear in order to offset the turn of the shoulders and balance the forward lean of the torso on landing after a serve.

Has anyone studied if this slows down preparation time for the return or allows players to more rapidly rebalance for the return? With a high speed camera it might be possible to see how well this arm movement works to speed up regaining balance.