My sister-in-law practices physical therapy in Boulder, CO. She sent me a link to her company's website that includes a very good section, "Learn About your Injury": http://www.altatherapies.com/eOrtho/index.php
The writing is very clear and concise. The anatomy graphics are also very good. Plus, for each injury various surgical vs. nonsurgical treatments are discussed.
I am 56. I would be interested in hearing how you older boaters keep fit and healthy.
Here in Cedar Falls(IA), we have a city Rec. Center that residents can join for $130 a year. Compare that to your run of the mill fitness center and it's a heck of a bargain. I like to get there 3 times a week, but usually only make it twice. Really a blessing in the winter when it's too cold(for me anyway) to run outside. As far as fitness specific to paddlers, I highly recommend exercises for your rotator cuff muscles. Even the Olympic Caliber weight lifters only do like 10# dumbells when they're isolating the rotators, so be careful when you first start out. Since I use most lifting muscles at my job, I may get some fitness from that as well. As Bill Endicott once said, "As much as possible, time in the boat" Scott Shipley also said," If you want to be a better whitewater paddler, spend more time on flat water." And Of course Gretsky's little gem,"Practice doesn't make perfect, perfect practice does." I'll be 59 later this year.