Serve Power & Spin: Tennis technique, drills and fixes

Once your basic serve is solid, speed and spin come from the same motion: legs and trunk load and drive up, the trunk tilts and turns just before the arm, and the arm whips up into a high contact. Research on high-performance servers shows a kick or slice serve uses about the same racket speed as a flat one; what changes is the direction the racket travels at contact, set mostly by your toss and trunk posture. From the side a camera can read your leg drive, the timing of your uncoiling, your racket drop (through your elbow and shoulder angles, since the racket itself isn't tracked) and your extension, not the ball's speed or spin.

Load the legs

Start from your normal serve: Continental grip, sideways stance, a controlled toss (see The Serve). LTA coaching uses the same Continental grip for flat, slice and kick serves, so you don't change grip to change the serve.

one grip, one motion, three serves.

Load into the trophy position: bend the front knee clearly (more than about 15 degrees) and let your hitting-side shoulder and hip drop back so the toss-side shoulder sits higher. This backward tilt of shoulders and pelvis is a trait of powerful servers. Legs and trunk produce roughly half (about 51 to 55%) of the energy that reaches your hand.

sitting into the legs, tilted back, toss-side shoulder high.

Drive up without a long pause. A short sit at the bottom of the knee bend is fine; holding the trophy pose bleeds stored stretch (one study measured upper-arm rotation about 20% faster with no pause than with a 1.5 s pause). Foot-up or foot-back both work: in tested players either style reached about 43 to 44 m/s racket speed, versus about 39 m/s when they barely used their legs.

a push off the ground that starts the swing, not a pose then a swing.

Uncoil hips then shoulders

Keep the tossing arm up and the trunk closed until the hitting arm starts forward. Dropping the tossing arm and turning the hips and trunk early leaves the hitting arm lagging behind and loads the front of the shoulder. In elite servers the upper trunk reaches its peak turning speed only about 0.06 to 0.08 s before contact.

the trunk turns a beat before the arm, not with the toss.

Rotate shoulder over shoulder: the hitting shoulder rises as the toss-side shoulder comes down, like a cartwheel, instead of spinning flat. This tilt is what lets the upper arm's inward rotation add its full share of speed.

climbing up to the ball rather than turning into it.

Drop, snap, extend

Let the leg drive throw the racket down behind your back. The drop lengthens the racket's path to the ball and pre-stretches the front of the shoulder. Let it come from the legs and a loose arm; don't force the arm further back, because extreme arm elevation and outward rotation are linked to shoulder impingement.

the racket falls behind you on its own as you rise.

Whip up to a high contact. In measured power serves most racket speed came from the upper arm rotating inward (about 40%) and the hand flexing through (about 30%). The forearm turning over (pronation) adds only about 5%; its main job is to square the strings. Reach contact with the arm long but not locked (about 20 degrees of elbow bend).

a loose throw that snaps through at the top.

Keep turning after contact. The arm's inward rotation and pronation continue into the follow-through; let the racket finish across your body so the smaller muscles at the back of the shoulder can slow it down gradually.

the arm winds down on its own, no braking.

Dial in power or spin

For spin, change the swing direction, not the speed. In 10 university players racket face speed at contact was about the same for flat, slice and kick serves; the flat serve was swung almost straight forward, while slice and kick were swung more sideways and upward (kick the most upward). In 12 high-performance players the kick serve's racket speed was only about 7% lower (about 40 vs 43 m/s) and travelled about 10 m/s sideways at contact versus about 1 m/s for the flat serve.

same effort, different direction.

Flat (power): toss just in front of you so you can drive through the back of the ball, strings facing the box you're aiming at, and turn the racket over (pronate) through contact. In the university study the flat serve was the fastest ball (about 180 km/h) with the least spin (about 20 revolutions per second).

driving through the ball toward the box.

Kick (topspin): toss further back, up over your head, and brush up the back of the ball. The change comes mainly from how your trunk is tilted and turned at contact, not from a different arm action, and contact sits slightly lower. In the same study the kick was the slowest ball (about 126 km/h) with the most spin (about 64 revolutions per second, roughly three times the flat serve). Don't reach the toss by hard, repeated arching of the low back; repeated hyperextension is a known risk for stress injury of the spine.

brushing up and across the ball rather than through it.

Slice: toss slightly to your hitting side and contact the outside of the ball (LTA describes it as 3 o'clock on a clock face), swinging out toward the side of the box. In the same study the slice sat in between: about 157 km/h and about 41 revolutions per second.

a sideways frisbee spin on the ball.

Feel it

Easy, whippy speed that comes from the ground up: knees bend, legs push, the shoulders tilt and cartwheel, and the arm snaps through at the top. If the serve feels like a shoulder push, the legs and trunk aren't doing their half. Spin should feel like the same hard swing aimed in a different direction, not a slower, careful swing. The app reads your body motion only: it can't see the toss, the racket face, or the ball's speed and spin.

Fix-its

Your serve is all-arm and slow Bend the front knee clearly at the trophy and push up into the ball. Tested players lost about 4 m/s of racket speed (about 39 vs 43 to 44 m/s) when they barely used their legs.
You open up early (tossing arm drops, trunk turns too soon) Keep the tossing arm pointing up and the trunk sideways until the hitting arm starts forward. Early opening causes arm lag and extra load on the front of the shoulder.
You pause at the trophy Make it one continuous motion: only a short sit at the bottom of the knee bend, then drive straight up.
You force the wrist or the racket drop Let the drop come from the leg drive and the snap from a loose arm. Pronation mostly squares the strings; muscling it adds little speed.
You slow the swing down to add spin Keep the same speed and change direction: toss back over your head and brush up the back for kick, toss to the side and hit the outside of the ball for slice.

Drill

Brush-up drill (LTA): hold the racket already behind your head, toss slowly and brush up the back of the ball. Start in the service box, move back to the baseline, then add speed and finally the full motion.
Same-effort contrast: alternate a few flat and kick serves with the same swing effort. Only the toss and the swing direction should change; if the kick swing gets slower, reset.
Leg-drive check: serve with your normal knee bend, then with a deliberately deeper load and push, and compare how much of the work your arm has to do.
Film from the side in slow motion (120 fps or more) to check knee bend at the trophy, the tossing arm staying up, the racket dropping behind you, and a long arm at contact. The arm phases are under a tenth of a second apart, too fast for normal 30 fps video.
Protect the serving shoulder: shoulder and elbow loads rise with serve speed, so build serve volume gradually, warm up first, and add posterior shoulder stretching, trunk rotation strength on both sides, and eccentric leg work for landing. Stop and get it checked if the shoulder, elbow or low back hurts.

Sources

Last checked 2026-10-26.