If, like me, you get laid up for ages by this condition - you are going to need some kind of exercise to keep sane. I have (despite all my preconceptions ) found yoga (in particular Astanga yoga) to be fantastic. I think Astanga suits me because of the flowing, moving cardio side to it and also a number of the poses provide lengthening (i.e eccentric) strengthening of the legs - just what you are after for tendinosis. The format of the classes (I got nowhere without an instructor) lends themselves to taking it gently and not over-reaching. I was amazed by how physically tired I got during/after these sessions and found them an amazing workout as well as leaving my muscles and tendons feeling warm, full of blood and well stretched.
I had always (as a runner, gym, bike, swim enthusiast) been a bit dismissive of yoga - but I'm a convert. You would need to find a class that suits your mindset, age, gender etc - and I would suggest that Astanga might be a good choice to suit the mindset of sports-mad people?
Go on...find a class, give it a try....at least you'll be off the sofa doing something..and you never know...you might catch the bug. I really like this poster (credit: http://dailycupofyoga.net/yoga-resources/) and love some of those bent knee standing poses - great eccentric strengtheners (but take it easy to avoid a flare up!)