See A-Z of rehabilitation exercises
This exercise is to strengthen the hamstrings muscles.
This first video is a straightforward hamstrings exercise.
In the second video as a progression we have added ankle weights and increased the speed and number of repetitions.
Here are some still images for anyone who cannot view the video.
Lie on your stomach on a firm surface.
Bend the one knee slowly.
Bend it as much as you are able.
Slowly lower it again.
Then slowly bend the other knee. Alternate, and repeat 10 times.