AKA Stiff-legged deadlift (incorrectly)
The straight-legged deadlift is one of the few exercises in weightlifting in which the back is actually flexed and extended rather than held in a static extended position.
Stand on a box with your feet in the pulling position, holding the bar in a clean grip, and your legs tight to keep your knees straight. Hinge at the hips and bend forward as far as you can, keeping your knees straight and the bar close to your legs. Return to standing by straightening the hips and returning your back to a fully arched position.
The straight-legged deadlift is often avoided because of the fear of back injury. It should not be used by athletes with existing back problems, and used only by athletes with good hip flexibility. Introduce the exercise in very small doses and with very light weights.
The straight-legged deadlift strengthens the back with dynamic work rather than the isometric work typically done in weightlifting. It can also be used for some variety and mobility.
Sets of 5-10 reps are most common. Weights should be relatively light and never heavy enough to force the athlete to noticeably strain.
The straight-legged deadlift can be done with a snatch grip. It can also be done without lifting straps for more grip strength work.