Brutal hamstring builder that bodyweight can't fake.
Keep your hips locked straight. Don't let your butt pop up to make it easier.
The glute ham raise loads the hamstrings the way almost nothing else does, through knee flexion while they also hold the hip straight, forcing them to work both of their jobs at once under your full bodyweight on a long lever. Lowering to horizontal takes the hamstrings through a savage lengthening, and curling back up demands they produce force from that stretched position. It earns its place as arguably the hardest and most complete hamstring exercise in the gym, with the glutes locking the hips throughout.
Your entire upper body is the resistance, acting on a long lever with the hamstrings as the only brake. Most people cannot do a strict full rep on day one, and that is normal. It is closer to a skill you build than an exercise you just do.
Push lightly off the foot plate with your hands or a stick to assist the way up, or loop a band from the front of the machine to your chest. Slow negatives alone also build the strength fast. Once strict reps are easy, holding a plate is the progression.
Same idea, knee-flexion hamstring work under bodyweight, but the GHD machine supports the thighs on a pad and anchors the feet, letting you hit a fuller range with less strain to set up. Nordics are the barebones floor version and are generally even harder to complete.
