Full arc extensions are a progression of short arc extensions.
Start without ankle weights and build up repetitions. Then when it seems too easy, add ankle weights (start with 500g).
In case you cannot see the video, here is a still sequence -
|Full arc extensions are exercises to work the quads. Sit comfortably on a chair.|
|Slowly straighten the bad knee and hold it in extension for 10 seconds, being sure to contract the quad muscles as much as you can.|
|Slowly lower the leg and repeat the exercise with your other, good, leg. Repeat this whole sequence 10 times. If this exercise is no longer a challenge, the number of repetitions can be increased, or you can add ankle weights.|