Hamstring-to-Quadriceps (H:Q) Ratio: What It Means for Your Knees

The hamstring to quadriceps ratio (H:Q) compares how strong the back of your thigh is against the front. The conventional version is usually quoted as about 0.6, and the functional version, which pits eccentric hamstring strength against concentric quad strength, sits close to 1.0 in fast knee extension. Lower ratios have been linked to knee and hamstring injuries in some athletes, but no exact number has been proven to protect you.

That matters if you squat, leg press and do leg extensions three times a week while curls get whatever energy is left. This article is part of our complete lower body and core training guide, and it covers what the numbers mean, what the research really shows, and how to balance your legs without turning it into maths homework.

What is the hamstring to quadriceps ratio?

H:Q is simply hamstring strength divided by quadriceps strength. In research it is measured on an isokinetic dynamometer, a machine that moves your shin at a fixed speed and records torque. In a normal gym there is no way to get the exact figure.

There are three versions you will see:

Ratio type	What is compared	Rough reference
Conventional	Concentric hamstring / concentric quad	About 0.6 (classic norm)
Functional	Eccentric hamstring / concentric quad	Near 1.0 in fast knee extension
Mixed	Eccentric hamstring at 30 deg/s / concentric quad at 240 deg/s	Used in some screening studies

The 0.6 figure is the traditional norm. A 2002 review notes that it has been central to the debate for decades, while also pointing out that it ignores joint angle and type of muscle action (Coombs and Garbutt, 2002).

Why is there a 0.6 rule and a 1.0 rule?

Because the hamstrings do different jobs. When you kick a ball or extend your knee fast, the hamstrings work eccentrically (lengthening under tension) to brake the shin and protect the joint. That braking job is better described by the functional ratio than by comparing two concentric contractions.

One Danish lab measured both. After correcting for the weight of the leg, the conventional ratio stayed within about 0.47-0.56 across speeds and contraction modes, while the uncorrected concentric ratio climbed from 0.58 to 0.74 as speed increased. For fast knee extension at 240 degrees per second, the eccentric hamstring to concentric quad ratio was 1.05 at peak torque and 0.89 at a 50-degree knee angle (Aagaard et al., 1995). The authors read this as evidence that hamstrings have real capacity to stabilise the knee in fast movements.

Note what that is: a measurement in one group under one set of conditions, not a threshold above which injuries stop. Gravity correction alone moved the numbers a lot, which is a good reminder to be sceptical of any single cut-off.

Does a low H:Q ratio cause ACL tears or hamstring strains?

The honest answer is “it is associated, but it predicts poorly.” Here is what each side found.

Studies that found a link. In a prospective study of professional footballers, those with a concentric H:Q below 50.5% had higher odds of a later hamstring strain (OR 3.14), alongside low eccentric hamstring torque and a previous strain (Lee et al., 2018). In 145 young female soccer players followed for a season, 13 tore their ACL, and those players had a lower H:Q (0.44 vs 0.50). They also had stronger quads, so the low ratio did not simply mean weak hamstrings (Taketomi et al., 2024). A cohort of 152 male American football players showed the same direction: 11 ACL tears, and a lower H:Q ratio was associated with them (Taketomi et al., 2024).

The pooled picture. A systematic review of prospective studies covered 18 studies with 585 hamstring injuries in 2,945 people, and 5 studies with 128 ACL injuries in 2,772 people. It concluded there is very limited evidence that H:Q is an independent risk factor for either injury, and the result did not differ between ratio types (Kellis et al., 2023).

Why they may disagree. ACL tears are rare, so single cohorts rest on 11 or 13 injuries, which makes results fragile. Studies use different tests, speeds and ratio definitions. And strength is only one of many risk factors, alongside sport, landing and cutting mechanics, previous injury, and plain bad luck. Interestingly, in a small study of female athletes, those with a past hamstring injury or ACL reconstruction had lower quad and hamstring strength than controls, yet the H:Q ratio itself did not differ significantly (Kellis et al., 2019). So the same ratio can hide very different legs: strong quads in one cohort, weaker legs overall in another.

Can lifting cause a hamstring-quad imbalance?

Yes, in the sense that programming can drift quad-dominant. The most common mistake is a leg day built from back squat, leg press, hack squat and leg extension, with one set of leg curls at the end when you are tired. Squats and presses do load the hamstrings, but they mostly work at the hip end and are not the same stimulus as bending the knee against resistance.

Two things worth knowing:

• Hip-dominant lifts like the Romanian deadlift train the hamstrings across the hip, as covered in our RDL guide.
• Knee-flexion work (seated or lying curls) trains the knee end, which hinges alone miss. See seated vs lying leg curls for the differences.

Which hamstring muscles do what is in our hamstring anatomy article.

How to balance your hamstrings and quads

Since no ratio is proven, the sensible aim is balanced, progressive training. This is coaching judgement built on the evidence above, not a validated protocol.

1. Count your weekly hard sets. Use the training volume calculator or a notebook. If quads get 14 sets and hamstrings 4, the gap is obvious.
2. Cover both jobs. One hip hinge (RDL or stiff-leg deadlift) plus one knee-flexion curl, trained twice a week where you can.
3. Train the lowering phase. Take 3 seconds to lower the weight on curls. If you sprint or play field sports, a gradual Nordic progression is worth considering (details in our Nordic curl guide).
4. Keep the two legs honest. Use single-leg work such as the split squat and single-leg curl, and bring the weaker leg up first. Our unilateral leg training guide covers the options.

Do Nordic hamstring curls improve the ratio?

Nordics build eccentric hamstring strength, which feeds the functional ratio, and the evidence on injuries is split. A 2019 meta-analysis of 15 studies in 8,459 athletes found programmes with Nordics had a risk ratio of 0.49 (95% CI 0.32-0.74) for hamstring injury, a reduction of up to about half (van Dyk et al., 2019). A later reanalysis argued only five of those studies truly randomised to Nordics. Using randomised trials only, the risk ratio was 0.56 (95% CI 0.20-1.52), an interval that includes no effect (Impellizzeri et al., 2021).

Why the gap? Mostly study selection: one analysis included non-randomised designs, the other did not. The cautious takeaway is that Nordics are a reasonable option for athletes, but the benefit is less certain than headlines suggest, and they are very hard, so progress slowly. Most recreational lifters can get plenty from curls and RDLs.

What about leg extensions and patellofemoral pain?

You may have heard that leg extensions are “bad for knees” and that strong hamstrings fix this. The studies above did not test that, so there is no evidence here either way. If leg extensions are comfortable, keep them and balance them with hamstring work. If they hurt, see a professional and read our leg extensions article.

Should I get my H:Q ratio tested?

For most lifters, no. Isokinetic testing is mainly used in sports clinics and rehab, and the 2023 review suggests the ratio alone is a weak predictor. It may help if you have returned from an ACL reconstruction or a hamstring tear and want to compare legs, and your physiotherapist can guide that.

When to see a doctor

Get assessed by a doctor or physiotherapist if you have knee swelling, locking, the knee giving way, a pop with sharp pain, or hamstring pain that does not settle within a couple of weeks. A strength ratio cannot diagnose any of these, and loading through an injury can make things worse.

The bottom line

The hamstring to quadriceps ratio is a useful idea with weaker proof than the gym internet suggests. Lower ratios show up in some injured athletes, yet a 2023 review found only very limited evidence that the ratio independently predicts ACL or hamstring injury. So aim for balance: a hinge and a curl each week, slow lowering, and two legs of similar strength.

Ready to put it into practice? Start with our leg day plan and make sure the hamstring slots are not an afterthought.