What this stroke shows
The reference is a two-handed backhand by the same left-handed player from 3DTennisDS. The body turns and both arms ride with the shoulders, so the shoulder turn carries the racket; the racket head reaches about 21 m/s (47 mph) at the ball. The ball lands about 2.5 cm past the baseline; with the simulation following the recording a little more loosely, the same stroke lands in.
Change the body
- Shoulders don’t turn, the chest turning only half as far past the hips: about 10% slower.
- Shoulders late, 40 ms after the hips: about 6% slower, into the net.
- Arms swing first, 60 ms before the body: a good 10% slower, and long.
- Hips turn half: about a third slower, and long. With the chest still turning as far, the loss is about 5%: a two-hander lives on the shoulder turn.
- Wrist released early, the bottom hand 40 ms early: about 10% slower, and long.
Change the racket at contact
- Face 5° more open: 1.3 m over the net and 11 m long, with half the topspin. Face 5° more closed: into the net.
- Swinging 5° more upward: 27% more topspin, as Cross’s rule of thumb predicts, and 0.9 m long. Swinging 5° flatter: 30% less topspin, a faster and lower ball 1 m inside the baseline.
- Contact 3 cm towards the tip: only about 1% slower. At 8 cm the ball is 7% slower.
Change the grip or the contact point
Moving the top hand halfway to a continental grip keeps the racket speed but takes the top-hand wrist to the end of its sideways range; a full continental grip cannot keep the same swing at all. Meeting the ball 20 cm higher raises the top-hand shoulder’s load from 28% to 105% of its measured strength.
Limits
One player, one stroke and a typical incoming ball. Where the landing changes with how closely the simulation follows the recording, the model cannot say where the ball goes.