In reference to Radek’s serve, Djokovic @ 1:01, left hand fully extended vertically to provide more shoulder over shoulder rotation, @ 1:07 pulls his left arm into his chest, mid-section to stop the 3rd link of coordination chain (hips to shoulders), so that the 4th link (shoulder to hand) can accelerate at maximum velocity.
HI Jorge,
In reference to Radek’s serve, Djokovic @ 1:01, left hand fully extended vertically to provide more shoulder over shoulder rotation, @ 1:07 pulls his left arm into his chest, mid-section to stop the 3rd link of coordination chain (hips to shoulders), so that the 4th link (shoulder to hand) can accelerate at maximum velocity.
Styrling