This is a quads exercise, for early rehabilitation, but after you are confident with static quads (quads sets/quads isometric exercises). By supporting the thigh the quads only have to lift the shin from the ground to extension. In the first video we are using a piece of ordinary PVC pipe you can buy from a plumber.
In the second video you see a progression - where a wider diameter tube is used.
Here is a close-up of the type of tube. Any plumber should have it. It is better than a rolled-up towel as you can be sure of always having a definite height.
Here are some still images for anyone who cannot view the video.
|Lie on a firm surface with the PVC tubing (or a rolled up towel) under your knees.|
|Straighten one knee. Keep it there for a count to five. Relax. Straighten the other knee and hold it straight for a count of five. Repeat routine 10 times|