Birdman, I have similar issues, but thankfully my arm strength had kept up this winter (except for conditioning/endurance)... This is way too complex of an issue to tackle @ once, but here's a couple of ideas.
Throw some of your lighter discs so that you are getting your arm stretched back out safely. I'd think trying to muscle the heavier/stabler discs might slow down your 'warm up'.
Maybe it's not your arm as well, it may be your approach. Give it some attention to see if your timing might be off - like being ahead of your disc too much when you should be releasing. Are you getting enough drive off of your back hip on that last step? Stay low to ensure leverage on that hip too.
Then, PRACTICE! PLAY! Jsut get otu there, take it easy for a couple of rounds, and you'll warm up in no time.