The Double Band Leg Curl is unreal for bringing up weak hamstrings. You set this up by placing a bench out side of a power rack and choke one band around each of the far ends of the rack. Slip one foot through each band and slide the bench back so you have tension on each band with both legs extended. You should feel an outward pull on each leg.
From this position you will begin to do seated leg curls. Since the bands are also trying to pull your legs apart you are getting a static contraction of the leg adductors. this essentially shuts these muscle off during the leg curl placing more work on the hamstrings. Curl the legs toward you body and pause when you reach the peak contraction of the hamstring. At this point return to the start position.
This is a great movement for bringing up weak hamstrings fast. I have seen this work best in three day rotations such as this:
Day 1: 2 sets 10 reps
Day 2: 2 sets 15 reps
Day 3: 2 sets 20 reps
Day 4: off
Day 5:2 sets 15 reps
Day 6: 2 sets 20 reps
Day 7: 2 sets 25 reps
* Keep building the reps with the same pattern until 2 sets 35 reps are done, then up the band tension and start over. After three weeks dump the movement and find a new one.
Other lifters have had success using this as you basic every day supplemental movement using a few sets of 10-15 reps.
The past 5 years has seen a dynamic shift in the approach to strength and flexibility training. These bands are the reason! Do not get left behind..