Could you give examples of some non weight-baring exercises to strengthen the quadriceps for people with knee issues?

Hi Marian,
The above info is great.
From my personal experince working with post-rehab clients, such as ACL,MCL, torn achillies etc.
It all really depnds on the clients fitness level before the injury.
And remember to always get a doctors clearance from the client before starting any physical activity.

All the best and good luck,
#shlomotrained