A comment to add to Ladyfishers -

I believe she is absolutely correct for starting out. It's just like skiing - the first day on the slopes, it feels like somebody hit you with a baseball bat for hours. By your 5th or 6th season it's a cinch. With spey casting, once the art is learned and the casting effortless (i.e. you learn to stay "within youself"), I think the stress is less than a single hander. One year guiding in AK I injured my right shoulder in a fall. I fished a Spey the rest of the because it hurt to cast a single hander - it actually had a theraputic effect. Not trying to play amatuer physical therapist her, just trying to point out that if done correctly Spey casting can be easier physically for some than casting a single-hander.