The all-arm serve is the one that feels powerful and isn't. You wind up, you swing hard, you feel your shoulder and forearm straining — and the ball comes off like a firm push rather than a crack. It's the most common self-taught serve there is, and the frustrating part is that the harder you swing it, the less you tend to get. Understanding why is the whole fix.
Push versus throw
A serve should be a throw: legs launch the body up, the racquet head drops and whips through, and the ball comes off like it was flung. A push is different — the arm carries the racquet up to the ball with the strings facing forward the whole way and shoves it over. No drop, no whip, no free speed, and every bit of pace has to be squeezed out of the arm and shoulder. That's why muscling it gives you less: you've taken the biggest engines (legs, gravity, the throw) offline and asked the smallest one (your arm) to do everything.
There's a tell you can see from behind: the shoulders. In a real throw, they stack — the hitting shoulder cartwheels up and over the tossing shoulder, so the racquet is thrown upward at the ball. In a push, the shoulders stay flat and level, and flat shoulders can only shove the ball forward, not throw it up.
What the camera reads
This one is a behind-the-server read, because a side camera physically can't judge how your shoulders stack. Filmed from behind, CoachVision measures your shoulder tilt at contact — how steeply the hitting shoulder sits over the tossing shoulder. A tilted, stacked cartwheel is the throw; a flat, level number is the push. If you've only ever filmed from the side, this read simply won't appear — that's the camera's geometry, not a gap in your serve. Film one from behind and the push shows up plainly.
The fix — Edge-First Pronation Serves
The push lives in a face that points at the net the whole way. So drill the opposite: lead with the racquet's edge toward the ball, and let your forearm rotate the strings through only at the last instant. If the strings face the net the entire swing, you're pushing; if the edge leads and snaps square right at contact, you're throwing.
Fifteen serves at half pace — slow is essential here, because you're rewiring a pattern, not powering through it. Feel the edge lead, feel the forearm roll the face through at the very end. That last-instant snap is pronation, and it's the difference between a shove and a crack. (Pronation itself is something the tracker reads from the frames, not a number — it lives between the keypoints — so trust the feel here more than any single reading.)
Then film a serve from behind and watch the shoulders start to stack instead of staying flat. When you throw up instead of pushing across, you get more pace from less effort — and you take the strain off the shoulder that the all-arm serve was quietly grinding down.