This movement can be cycled several different ways. For example, it can be done at the end of your training for standard sets and reps, or it can be performed using the timed method where you try to do one rep every five to ten seconds for several minutes. During the time you're resting, make sure to keep some tension on the muscle.
Band leg curls can also be performed during an extra workout. I've used this method with many athletes who have weak hamstrings. Start with five reps on each angle (straight ahead, off to the right, and off to the left). This would be a total of 15 reps. Over the next couple of weeks, add one rep to each angle. After ten days you'll be up to 15 on each angle or 45 total reps.
Also, make sure to skip a day every now and then for better recovery. I'd suggest a three on, one off schedule.
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