Short arc quads
This is the next stage in the quads regime and aims towards achieving the straight leg lift (below). The idea with this one is to raise the knee using a wedge (rolled up pillow or towel will do) preferably on a solid surface and then to push the knee into the wedge in order to try to raise the foot. Once the lift is achieved, hold for 5 seconds and slowly lower, keeping control of it as you lower it down.
Straight leg raises
See separate post on this one. But basically it goes like this ... flex ankle upwards, push knee down into bed to lock leg straight, then raise your foot until the leg lifts off the bed. Try to raised it about 10 inches off the bed, hold for 5 seconds, then lower slowly back down. Try not to let the leg bump back down, this one's about control. Repeat 5, then 10, etc.
Full arc extensions
This one builds on the short arc and helps to make the straight leg raises become easier by working on the quads again. Sit on a firm chair with leg bent at 90 degrees. Slowly start to raise leg, aiming to get it straight out in front of you (you may not make it that far at first). Hold for 5 seconds, repeat 5-10 times. Increase reps and holds as it becomes easier.
Standing wall slides
This one will work the quads and improve lower leg strength. Stand near wall, feet slightly apart. Place your hands on the wall for support (but don't lean on them), slowly slide up and down 10 times. Progress to holding for 5, repeat 10 etc. You don't need to bend too far to begin with, just as far as is comfortable. Try not to lean to one side, favouring the good leg - I did this, and its apparently "cheating"!