Va has to do with load factor, stall speed and structural design limitations; not full control movements.
An airframe is designed to withstand a certain stress. This stress is independent of weight.
Load factor is the ratio between the lift produced by the wings and the weigth of the aircraft. When lift equals weight, the load factor is 1, and when lift is twice that of the aircrafts weight, the load factor is 2, etc.
Since load factor is depenent on weight, the design load limit expressed in G, not N, is dependent on weight.
Stall speed is a function of load factor. As load factor increases, stall speed increases by a factor, the square-root of the load factor.
Because stall speed is dependant upon load factor, there will be a certain stall speed corresponding to the design load limit. If an aircraft is flying slowly, and the load factor for some reason increases, the airplane will stall before it reaches its design load limit. If the airplane is flying with great speed, and the load factor is increased, the airplane will not stall until after the design load limit has been exceeded.
The dividing speed is the maneuvering speed, and it is the speed at which the airplane will stall just at is reaches the design load limit. Because stall speed varies with load factor, and load factor varies with weight, the maneuvering speed will be a function of weight.
Va is simply a stall speed.