Need to build legs, but have bad history.

[slugger28]

Here is my story. I am 39 years old. Been an athlete all my life and my legs reflect that now. I have an arthritic left knee and i blew out my achilles tendon over two years ago. I am 6'3" and 205 pounds in good overall shape. I have started in the past year to give up the athletics and started lifting regularly. Now, to my problem. My knee and achilles make it very difficult to build my legs, but they are my worst feature...pretty thin legs, but i have a tough time with lunges and squats as it results in moderate pain after the workouts.
Is there anyway (exercises or programs) to slowly build muscle mass in the legs without a lot of stress on the legs.

Thanks

[marwino96]

what kind of sports where you involved in? Did you not lift before?
Have you tried machines, legs and ham extensions? They won't do what squats and lunges will but if you start with machines, then graduate to squats you might be able to handle squats.

[hrpiii]

as suggested, start with some machines.. and hit some high reps, like 50 reps per set. Legs love some high rep stuff.