Hamstring workouts at home

The hamstrings are important when it comes to supporting knees.  Strengthening hamstrings does not require any equipment.  You can do useful exercises with just a mat.  The exercises in the first video take about 8 minutes to finish, assuming you can do them all without any rest in between.  The second video sequence takes about the same amount of time, but includes a slightly different set of exercises.  The third video has six exercises (5 min for demonstrations) and includes a few exercises I did as part of knee rehab physical therapy.  Although all the videos include double and single-leg bridges, they are done differently.  The first are done on the floor, the second uses a chest of drawers (instead of a wall or chair), the third is the hardest.  I sometimes do bridges using a stability ball, which adds a little bit of core work.