"I like the way the seam runs up the back of the stocking..." Yeah, me too. But what David Lee Roth should have said after that is: "especially when it has to take the long way--cuz she's got such monstrous hamstrings!" :P
The hamstrings, much like the quadriceps, features a few different muscles working together as a group. The primary muscles commonly included in the "hamstring" denotation are the inner and outer head of the biceps femoris (the larger and more prominent "'head' of the hamstring" is made up of mostly the long head of the biceps femoris), as well as the semitendinosus and semimembranosus muscles (the two thinner muscles which make up the "striated" looking area of the inner rear thigh). Part of the adductor magnus is also included as part of the hamstring group. Here's an example picture:
So when trying to develop the "hamstrings" to the appropriate size (enormous), it is necessary to develop each of these muscles. Multiple muscles in a group means using a variable approach is necessary, just like with the quadriceps; incorporating closed- and open kinetic chain exercises, a variety of hip positions, as well as activation at the hip and the knee in each workout is an absolute must. And just like with the quadriceps, the hamstring is capable of withstanding incredible forces and therefore must be maximally overloaded. Think of how little overload it would take to illicit adaptive response in the upper body when the upper body is untrained--but even an untrained individual is using their legs every day, so the quadriceps, "hamstrings," and calves all naturally require even more overload in order to grow.
Once again, during hamstring movements you want to keep your toes flexed towards the knee--pointing or inward rotation allows the calves to pick up some of the slack, especially during open-chain exercises, i.e. cable leg curls or seated hamstring curls on a machine. Similarly, you want to keep your hips in a neutral position during most exercises--this will help stabilize the hips and lower back, minimize twisting during unilateral exercises, and aid in isolation during both unilateral and non-unilateral movements. During an open-chain exercise such as lying leg curls (on a machine or with dumbbells), allowing the hips to come up slightly during the flexion portion of the exercise will, in some instances, activate the "inner head" of the hamstring to a greater extent. Play around with hip tension and position and find what makes your hamstring(s) work hardest!
Something I haven't mentioned before, but that applies to this muscle group as well as it does to any other: isolation of a certain area of a muscle group is never completely possible--that is, you can never fully isolate "inner" or "outer, "upper" or lower"--the entire muscle will always be working to some extent. That being said, it is still necessary to isolate the chest from the shoulders, the calves from the hamstrings, etcetera. And always, ALWAYS feel the muscle working--push your brain into your muscle fibers and control them completely--you can doo iiit!
Thanks for the awesome shirt KB! <3