Lee, your link shows more what I do now. A straight legged deadlift is more like this link. This is the version that hurt my hamstring. As you can see there is less action in the knee despite it being slightly bent. Your version has a lot more bending in the knees involved.
Exactly, the link I gave is to a traditional deadlift, they way my mama taught me, no need to further specify with a modifying element preceding the noun head. The knees bend and the quads do their fair share of the work. This is also the way you're supposed to lift boxes when you're moving
.
I'm not a functional fitness guy, but I do think most if not all lifting movements should be 'natural' in the sense of moving in the planes, angles, and arcs for which our joints and muscles were designed (by evolution, god, or aliens). I can't think of anytime I would want to lift something with my knees stiff or locked out, but for bodybuilders interested in hamstring hypertrophy, I can see how the straight- or stiff-leg deadlift may have its place. Seems pretty similar to Good Mornings, but perhaps because you keep the weight closer to your COG with the straight-leg deadlift the latter might entail less stress on the back. I may check it out--I'm always ready to tweak my routines if something better comes along, provided it doesn't tweak my body (I added leg curls back in last year, even though this is a pretty artificial movement for your hamstrings and glutes). According to the Exercise Prescription site (which is my go-to site for this stuff, as it avoids a lot of the gab found in YouTube Videos like the one you posted), the straight-leg deadlift (
http://www.exrx.net/WeightExercises/ErectorSpinae/BBStraightLegDeadlift.html) isn't necessarily bad for your back when done right:
http://www.exrx.net/Questions/DangerousExercises.html#anchor416052. I also like to do incline sit-ups--both straight-up and obliquely--which are supposedly bad for your back.
Still, the straight-leg DL seems like an unnatural movement, like the Cuban Press, which Abide suggested some time ago, but which for me felt like too much strain on my rotator cuff. So I'm kind of skeptical.
Edit: Finally, I think you have to consider whether one's hamstring will benefit more doing a straight-leg deadlift at low weight, or a regular deadlift, utilizing the hammies naturally, with 3-4 times the weight, in addition to squats and power cleans. A lot of these rinky dink variations seem like a waste of time to me. Especially for the lower body. I do a fair amount of low weight variations for my shoulders, but that's because I've had some issues with them, and so want to make sure the joint is strong and mobile. Plus, the shoulder has a huge range of motion, so you kinda have to attack it from many different angles.