Many elements are combined to produce the serve – and one of the secrets is to have all the elements firing in the appropriate sequence.
Timing – we have all felt the effortless hits and unfortunately we all have at one time or another, felt the effortful hits.
One of the most important sequence during the serve occurs with regard to the racquet drop and the knee bend.
In general, on the serve, one must fire in quick sequence large muscles first leading to smaller and then smaller muscles, culminating in a whip at the top of the swing.
As regards the racquet drop and knee bend, the best one I heard on this was from Vic Braden, who said, “Fire the extensors baby!”
Check this one out – it makes sense and will help – guaranteed.