> Arm is not supposed to be using much muscle to swing the racket.
That's true with higher SW racquets but I think that those using lighter racquets are using arm swingspeed to generate power and spin. It's an adjustment both ways. When I first used the PDR, I was wondering where the power was because I was used to plowthrough and a relatively slow swing which doesn't work that well with a PDR.
4 x IG Prestige MP, 70 cm, 376 grams, 386 SW, ALU Power @54, Prince Syn Gut 16 @58