i think i'm posting too much on topics i don't really know alot about (since i'm not a doctor). ..but, i personally think (supposition here) that stretching too much sometimes does make the hand very sore and could lead to CP. i tend to like to play more bach, scarlatti, schubert, beethoven, etc. and sort of 'avoided' chopin, debussy, etc. in the past. but, with the teacher i had at wcu - he showed me the 'zip technique' (yes, not again

) and it really made a difference in how my rh especially felt.
i have always had a bit of difficulty with playing my left hand as evenly as the right. maybe i'm sort of stunted in piano a little bit - but, i still believe the key to playing large leaps and stretches is to use this 'zipping' around. it leaves your hand in a comfortable mold (like around a ball that has gone slightly flat) and for me give me the comfort as one gets with an arch in a shoe. if you walk around completely flat footed all the time, you get sore. so, maybe the combo of a little give and take (with arch) and zipping - you have some techniques to try.
*i have yet to find on the internet an explaination of this technique as good as my teacher explained. it is basically playing the lower note and then moving the hand sideways very quickly to the next note. you don't stretch a lot.
the warm and cold water might just be a good thing - but only after a 1/2 hour? was wondering about that? 1/2 hour of exercises or something? i do a LOT less exercises than i did before. basically, they wear your hand out when you're old like me. i want to save something for my pieces - so i just start in on difficult places and work them a few times. overdoing anything (sports, etc) seems like it does have it's hazards.
i like to play difficult passages for a while (before major tiredness of the hand) and alternate with easier stuff that doesn't require a lot of stretching. this alternating back and forth helps, too. playing lighter helps.