Quote from CONF_iture:
"[...] Alpha max is an AoA that the FCS maintains at the fixed value Airbus decided to adopt depending on the configuration.
The corresponding speed to that fixed alpha max value is called Valphamax and remains the same as well, be it in level flight descent or climb ... The amount of thrust will decide the V/S but the speed will remain at Valphamax."
The process of changing the FPA requires a force. Can you go on and explain how that force is produced?