ohhh I am with you on the sore arms, I have been swimming with the masters 1x/wk and on my own another 2x/wk. On the weekend we did the most difficult set for me yet- after a lengthy warm up and some drill sets the main set was
5 x 200 free descending on 3:30 and repeat!
I must admit the only thing that was descending on the 2nd set of 5 200's was my rest time!!! I was glad I made it though even if my head seemed a long way to lift my arms for shampooing afterward