Thoughts on hamstring curls

Posted on May 21, 2012

(Last Updated On: February 9, 2018)

Because I recently had ACL surgery and used a hamstring as my graft, strengthening the hamstrings is something that has been on my mind lately.

Just a quick primer: The hamstrings perform two main movements, hip extension and knee flexion.

Hamstring exercise

Credit to TrackMom

Hip extension involves bringing the leg backwards, like while walking. Knee flexion consists of bringing the heel to the butt, like a leg curl.

A lot of people in the powerlifting / strength and conditioning community love to proclaim all you need to strengthen the hamstrings is hip extension exercises. That we do way too many leg curls, that leg curls suck, and exercises like squats, deadlifts, good mornings, etc. are all you need.

These people have clearly never had or worked with someone who had reconstructive ACL surgery with a hamstring graft.

From personal experience I can tell you my hip extension strength, i.e. movements like squatting, deadlifts, good mornings, is fine. In fact, it has been fine nearly the entire time after my surgery.

My knee flexion strength (like a leg curl) is not. It has been excruciatingly difficult and tedious to regain.

One of the issues people have doing leg curls is they have poor form. They are often performing lumbar extension during a leg curl rather than pure knee flexion.

Here are some examples:

There are a couple of issues going on here:

1) People try to use way too much weight.

2) The posterior trunk is stiffer than the anterior trunk. Specifically the lumbar extensors are stiffer than the external obliques.

Lumbar extensors. (From exrx.)

Said another way: The lumbar extensors are overpowering the external obliques. Therefore, the pelvis anteriorly tilts and the movement becomes much more a lumbar extension exercise than a knee flexion exercise.

So that’s kind of the intro into this. The next issue is something I discovered recently. I am just about fully there in the process of trying to regain my hamstring strength in movements like the videos above. However, I’ve noticed during something simple I still have issues. For example, if I try to bring my heel to butt while standing (like say I was trying to look at the bottom of my shoe), it is really hard.

This didn’t make sense to me. By all indications my hamstrings are nearly as strong as they used to be, and nearly as strong as my non-operated side.  Something isn’t right.

Then the last month or so my lower back has sporadically been bothering me. Sometimes I’ll have issues due to being on my feet all day, helping load and unload weights, leaning over a ton, etc. But the past month it has become much more severe. And nearly any time something at the lower back is going on it’s almost always indicative of the lower back moving too much.

So one day I look in the mirror while I attempt a leg curl. And I notice this:

You can see I’m getting quite a bit of my leg curl by performing hip flexion. Not ideal. Next, when I keep my knees together to prevent any hip flexion, watch my lower back and pelvis:

It’s not dramatic, but you can see my lower back and pelvis moving quite a bit when I attempt a leg curl. As well as my entire upper body leaning forward.

This is not good.

When I keep my pelvis and lower back as still as possible, and prevent any hip flexion, this is how much I can move my leg:

I can barely flex my knee at all.

But during typical leg curl machines my hamstrings are nearly symmetrical in strength, and I have no issues, why is this happening?

Look at the position of the hips during a couple of typical leg curl exercises:

The hips are always flexed! Therefore, when the hips are in a flexed position my hamstring strength is good. But when the hips are in a neutral or extended position my strength is not good.

That’s one reason why my lower back and pelvis wants to move during a leg curl. My body is trying to put my hips and hamstrings in their strongest position (hips flexed). It’s just that position is not good for my lower back.

Also, I bet a lot this had to do with getting a hamstring graft. After a hamstring graft for ACL reconstruction your knee flexion strength becomes very, very weak. I’m willing to bet a lot that after my surgery I started using my back to help achieve knee flexion and hip extension due to my hamstring being so weak. (Literally a part of it was cut off.)

Either way though, this is important because of the training implications for the hamstrings. The hamstrings are rarely functionally used to curl the leg when the hip is flexed. They primarily extend the hip, and then help to curl the leg when the hip is in an extended position.

Also, you need to be wary of training the hamstrings too much in the hip flexed position due to the compensatory patterns that can occur. As I talked about, issues at the lower back can arise. Issues at the knee can arise too.

Let’s go over the proper form:

1)   Before anything moves the pelvis and lower back should be in a neutral position.



2)   The knees should be touching one another. This provides a self-feedback tool for letting you know whether or not your hips are flexing:



3) Make sure when curling the leg no rotation at the knee occurs. Lateral rotation is the most common, and results due to a tight IT Band. See The Best Damn IT Band Stretch Ever for more.

The foot should be straight and in line with the knee, maybe even rotated inwards; it should NOT be rotated outwards like this:

4)   Absolutely, positively, ZERO movement occurs at the pelvis / lower back. This is much harder than you would think. Especially for people with any knee or lower back pain history. It helps to tighten your stomach to prevent lumbar movement.

Here is  a video with better form:

Give it a shot with you or your clients. I think you’ll be surprised with how difficult it is.

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