Some key types of stretches for hamstring flexibility are static, dynamic and PNF. With flexible hamstrings, an athlete should be able to raise a relaxed, straight leg vertically at least 90 degrees. A hamstring is tight if the leg cannot go beyond 80 degrees.
A static hamstring stretch is possible from a seated, standing or lying position. From a seated position, an athlete extends one leg straight while leaning forward. From a standing position, an athlete elevates one leg while leaning forward. From a lying position, an athlete raises a straight leg upward.
In a dynamic stretch, an athlete kicks a straight leg upward as high as possible, and in a PNF stretch, an athlete pushes a straight leg against resistance.