Well I learned that strech from my football coach ("bend over and PUSH!") and it was never corrected. I guess the partner streches we did where you push down on your partners rounded upper back are just awful.
FYI - I found out about this becasue my PT recommended the "McKenzie Method" and we're doing that. Good intro here:
I find doing them one leg at a time is better anyway.
Isn't it better to do them standing, or maybe using a tilted bench? I've tried to anteriorly pelvic tilt sitting on the ground and while it is a better way to target the hamstrings, there's not really any weight on it. It'd be nice if we had a weighted pulley to help bring us forward.
I bet those decline benches would be good when you'd doing the thing lying on your back pulling the leg up because lying flat you need to get past 90 degrees of flexion before the leg even starts to help the stretch with its own weight. On a decline bench this would happen earlier.
Upside down would probably be best but it'd be too stressful to anchor, I think that's why the standing stretch could be better for those of us starting out. We can always put one leg in front of elevate it to take some weight off the increasedly stretched leg and put it into further hip flexion.
I stretched with a rounded back like that my whole life until my first yoga class. It's only natural, when you think about it. In school when they did PE test and measured flexibility, they can't easily measure the angle you can flex to, but they can measure how far your hands move. By rounding the back, you push the fingers a little further towards/past the toes. We probably all learn it wrong from day one.
What the yoga instructor told me as a basic rule of thumb that has helped me a lot in my stretching, unless you're targeting the back specifically, the back muscles should be holding the spine in it's natural state. This seems to be true for weightlifting too.
After the first few classes my back would ACHE (in a good way) from all the isometric flexing. But I have a much stronger lower back now for it.
I stretch my hamstrings lying on the ground, one at a time. I will use my arms, or a belt if I must, but I prefer to use a doorway.
Put your ground leg through the door, and keep it and your back flat on the ground.
Bring your stretching leg up into position while bent, placing your heel on the wall.
Slowly straighten your leg to full extension, using the wall as your support.
Mark progress by how close your bottom is to the wall.
I've got short hamstrings, so this is rough work for me, but if I get to where my legs can comfortably make that 90 degree angle while in that position, I suppose I'll start bringing the leg farther by hand.
Hamstrings are interesting in that a LOT of people say they have tight hamstrings, but that could actually be the opposite of the truth. They may feel tight, but the reality is if your hip flexor complex is tight, that will push your pelvis into lordosis (anterior pelvic tilt) thus lengthening your hamstrings and consequently making them feel "tight" because they are already in a stretched position.
My other little nugget of knowledge on hamstrings is that when stretching them you want to push your pelvis square. Go as far as to flex your glute on the non-stretching side so that everything is in line. My hunch (unproven) is that this is why people are less flexible stretching their hamstrings bilaterally.
The theories presented by these folks go a long ways in shaping my practice.
Without going into too much detail, there are "trains" of muscle, connective tissue etc. that can affect posture and movement in profound ways.
One of the more common problems i see involves this tract;
and the hamstrings are a large part of the issue.
My suggestion is to start at the feet and calf, as a 'plantarflexed' ankle causes a cascade of postural compensation including (but not limited to) the anterior pelvic tilt mentioned above. (in the "superficial back line", note the images of the little girl at the end, esp her ankle)