Creating racket velocity on serves and strokes
Many players have great difficulty creating great spin with their loops and serves. They stroke through the ball with a constant not-too-high velocity, and the result is a not-too-great spin. There's little acceleration in their shots, and so there's little velocity.
There's a distinction between speed and acceleration. Velocity is the actual miles per hour; acceleration is how fast you are speeding up. To get a lot of velocity, you need a lot of acceleration. For maximum velocity, you need to accelerate right up until contact. How do you do this?
For looping, start with the lower body muscles, and work your way up. This means the legs, then waist, then shoulders, then arm, then wrist. Think of it as a whip, which also starts at the base (near the handle) and works its way down to the tip. This is especially true when looping and serving. Rotate your body around in a circle, creating great torque. You do so by using the muscles exactly as noted above, in that order - legs, waist, shoulders, arm, and then wrist.
On serve, you generally don't use your legs much, but for forehand serves you do rotate the body into the shot from the waist, shoulders, and arm. Then the wrist snaps into the shot like the tip of a whip, generating massive spin.
If you wave it, what moves faster, the tip of a whip or the tip of a stick? The tip of the whip. To maximize acceleration, you need to relax your muscles as if they were rubber. If they are tight, you'll have the velocity of the stick.
Ultimately, power comes from good technique (muscles used properly and in synch) and relaxed muscles.
Professional Table Tennis Coaches Handbook