Do Squats Work Your Hamstrings?

Key Points:

Hamstring muscle activity in the squat is low compared to exercises like good mornings, stiff-legged deadlifts, and leg curls.
Squat training twice a week for 10 weeks yielded no muscle growth in the hamstrings (~0.6%), while the muscle volume of the quads, glutes, and adductors all increased by 5–7%.
From a biomechanical standpoint, it makes sense that your hamstrings aren’t very active in the squat, as they directly oppose your quads, which are prime movers in the squat.

Do barbell back squats work your hamstrings?

Depending on who you ask, you are bound to get different answers.

My answer?

Not really.

The idea that your hamstrings are important for your squat has been around for decades, but is slowly losing ground as new research disproves it. Sure, your hamstrings contribute to joint stability and some hip extensor moment, but as you’ll learn in this article, your hamstrings are involved far less than your quads, glutes, and adductors.

And as far as hamstring exercises go, the squat is a really bad one, as you’ll see.

Let’s begin by taking a quick look at the hamstrings muscle.

Hamstrings Role in the Back Squat

Your hamstrings cross over both your hip joint and your knee joint. As such, they can act upon both joints with:

Hip extension. Extending your hip, like in the Romanian deadlift or the good morning.
Knee flexion. Flex (bend) your knee, like in a leg curl.

Additionally, the hamstrings are important antagonists to your quads, responsible for decelerating your leg when you’re swinging it forward while walking or running.

Three out of the four hamstring muscle heads cross over your hip joint, while all four cross over your knee joint.

Because of this, any force generated by your hamstrings is in direct opposition to your quads, which are already challenged very hard in a squat.

From a biomechanical standpoint, it is more efficient for your body to first utilize the powerful hip extensors that are your glutes and adductors.

In fact, a study using biomechanical modeling suggests that it would be very inefficient if your glutes and hamstrings shared hip extension moment demands equally (50/50), as that would tax your quads to the point that you’d have to use about 80% of the weight that we are actually capable of in the real world.¹

However, biomechanical modeling only gets us so far in this matter. We want more evidence to map out our understanding of the hamstrings’ role in the squat.

Hamstring Muscle Activity in the Squat

By measuring electrical activity in muscles during exercise, we can get a gross estimate of how much various muscles are worked in different movements.

An American study² tested quadriceps and hamstring muscle activity in 34 collegiate athletes at their 6RM (about 85% of 1RM) in different exercises:

The results?

Barbell back squats had the lowest hamstring activity of all tested exercises: only 27% of MVIC (maximum voluntary isometric contraction).

Hamstring muscle activity in the barbell squat

Squats also had by far the highest quadriceps muscle activity of all exercises – six times greater than that of the second-most quad activating exercises above, which was the good morning and the stiff-legged deadlift.

Expressed as an H:Q (hamstrings:quadriceps) ratio, this put squats well at the rock bottom of the tested exercises.

Hamstrings to Quadriceps ratio of muscle work in the squat

This further implies that the squat is an exercise that, as far as thigh muscles go, trains your knee extensors (quads) and not your knee flexors (hamstrings).

Do Your Hamstrings Grow From Training Squats?

If squats work your hamstrings, surely the hamstrings would grow from squat training then?

It turns out that they don’t.

A recent study from Japan had participants train squats twice a week for ten weeks.³ They did 3 set x 8 reps per workout and added weight whenever they completed all 3 x 8 reps. A sound training program to build muscle, or, at least the muscles worked in the squat.

They used MRI to measure muscle volume in the hamstrings, quads, glutes, and adductors before and after the training period.

Results?

Great – for the quads, glutes, and adductors. For the hamstrings; not so much.

The hamstrings didn’t grow at all, while the prime movers saw a typical 5–7% increase in muscle volume.

So – Do Squats Work Your Hamstrings?

Taken together, where does this put us?

Biomechanical reasoning. The hamstrings cross over two joints. Any force exerted by the hamstrings must be counteracted by the quadriceps, which are already taxed hard in the squat.
EMG activity. Hamstring muscle activity in the squat is low, far less than quadriceps activity and hamstrings activity in exercises more suited to hamstrings functions.
Squats don’t train the hamstrings. Evidently, training squats will cause your quads, glutes, and adductors to grow – but not your hamstrings.

In conclusion, I think it is safe to say that: No, squats don’t work your hamstrings. At least not to any meaningful degree.

Squats don’t make your hamstrings grow, and the hamstrings aren’t very active in the squat compared to better hamstrings exercises.

As for contribution to your squatting strength, computer modeling puts it at 35% at best, but that is only after the adductors have been maximally taxed, and it always comes as a direct cost for your quadriceps – which are probably the muscles that limit your squat strength anyway.⁴

Hamstrings muscle in the barbell back squat

In fact, if you would have really strong hamstrings and use them a lot in the squat, it would severely limit your quads’ knee extensor moment and turn the movement into a good morning squat. At which point, increasing your quad and adductor strength would probably be very low-hanging fruit for improving your squat 1RM.

But My Hamstrings Get Sore From Squats!

Do they really? Or do you confuse your hamstrings with your adductor magnus, the single largest muscle on the back and inside of your thigh, that is also a primary hip extensor in the squat?

The adductor magnus is a large, but fairly unknown muscle that sits on the inside, posterior (back) portion of your thigh. In most people, it is the largest or second-largest individual muscle in your thighs, only rivaled by vastus lateralis.⁵ ⁶

The adductor magnus is your most important hip extensor in the deep part of a squat, which is also the most challenging part. And, unlike the hamstrings, it actually grows from training squats.

If you are sore in the back of your thighs the day after squatting, chances are that you are sore in your adductors, not in your hamstrings.

Take-Away and Practical Applications

Let’s summarize, and see what you should do with this information.

Squats don’t work your hamstrings to any significant degree. Hamstring muscle activity measured with EMG is low in the squat, and the hamstrings doesn’t grow from squat training.
While the hamstrings can contribute up around ~35% of your hip extension moment in the sticking region of the squat, they do so at the cost of increasing the burden of your quads, which are already taxed very hard in this position. Compare this to the adductor magnus that contributes ~55% of the hip extension moment in the sticking region, without adding to the burden of your quads.
If you want to get stronger in the squat, you should primarily focus on strengthening your quads, glutes, and adductors. Even if you would have super-strong hamstrings, it is biomechanically inefficient to use them overly much in the squat, as your quads have to counteract their joint moment forces.
If you want to train your hamstrings, the squat is a poor choice compared to pure hamstring exercises like seated leg curls, good mornings, stiff-legged deadlifts, and Nordic hamstrings.

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Good luck with your training!