Machine Leg Curl vs Glute-Ham-Raise

Question

Often when arguing about the Leg Curl Machine being bad (eg. hurt your knees in many cases), people refer to the Glute-Ham-Raise as a way better (less harmful) alternative.

To me, the movements of the Machine Leg Curl and Glute-Ham-Raise look very alike. The arguments of Machine Leg Curls being bad for your knees can also partially applied to the Glute-Ham-Raise:

• knees are fixed -> sheer forces on the knees
• hip is not involved in the movement (stays straight in the case of the lying Leg Curl)

The only noticable difference to me personally is, that in the Glute-Ham-Raise you lift your body and in the Leg Curl you pull the arm of the machine towards your butt. So, again to me, they look very similar.

Where excactly is the difference between these two, and why are the Glute-Ham-Raises often told to be a way better option?

Answer 1

There's just entirely different exercises, honestly. The only similarity is that you're contracting the biceps femoris. Compare the muscles used for the GHR vs the leg curl, you'll see the difference.

It's also built into the name, the GHR is the glute-ham-raise, and the glute portion there is key. The leg curl is, well, just a leg curl.

I'm really not sure where the leg curl is bad for your knees, that "bad for your knees" argument seems to be tossed around in gyms for everything that someone doesn't want to do, valid or not.

The hamstring (biceps femoris) are attached to the pelvis, which in turn is attached to the spinal muscles (erector spinae). You're not fully engaging a muscle unless you also engage its connected parts, which is why compound multi-joint exercises are so highly regarded and form the staple of all effective strength training programs.

So unless you engage your back and glutes, which the leg curl does not in any meaningful way, you're not going to really engage your hamstrings as much. Further, is the goal to develop a strong posterior chain? If so, then a compound movement like the GHR is substantially more effective.

Arguments could be made for the leg curl, but if you have a GHR and a leg curl machine available to you there's little reason to opt for the leg curl. Go heavier or do more reps on the GHR, and use the leg curl machine just like the Smith machine: as a place to hang your towel.

Drilling it even further, this is backed up by peer reviewed EMG results:

Therefore, athletes and coaches who seek to maximize the involvement of the hamstring musculature should consider focusing on the glute-ham raise and RDL.

Answer 2

One important difference is that a leg curl exercises the hamstring muscles over the entire range of motion of the knee joint. The glute-ham raise can only exercise the hamstrings from 0 degrees (lying flat) to 90 degrees (sitting straight up) of knee flexion. And closer to 90 degrees, the force the hamstrings are exerting gets very small. So if you want to exercise the the hamstrings over the full range of motion of the knee joint, a leg curl is definitely better than a glute-ham raise.