This article is from the Stretching FAQ, by Brad Appleton Brad_Appleton@ivhs.mot.com with numerous contributions by others.
Now that our calf is stretched, we can get a more effective hamstring
stretch (since inflexibility in the calf can be a limiting factor in this
hamstring stretch). Still sitting on the bench in the same position,
straighten your leg out while trying to hold onto your outstretched leg
with both hands on either side as close as possible to your heel. Starting
up with your back straight, slowly exhale and try to bring your chest to
the knee of your outstretched leg. You should feel a "hefty" stretch in
your hamstring and even a considerable stretch in your calf (even though
you just stretched it). Hold this stretch for about 20 seconds.
Now for the isometric stretch: when you have gotten your chest as close as
you can to your knee, try and put both hands under the bench by your heel
(or both hands on opposite sides of your heel). Now grab on tight with
your hands and try to physically push your heel (keeping your leg straight)
downward "through" the bench, the bench will provide the necessary
resistance, and should prevent any leg motion from occurring.
 
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