If the muscles are too weak to do a heel slide unassisted, you can use your hands to just start the heel sliding and control the movement.
Here is a still sequence if you are unable to view the video.
|With your back supported and the one leg bent, use your hands to grasp the knee of the straight leg and gently help the muscles bend the knee, with the heel sliding on the tea tray.|
|Slide the heel until both knees are bent.|
|Relax for a few seconds and start to slide the heel back down again. Repeat with the other leg. Repeat the exercise 5 to 10 times.|