Hamstring injuries are the source of much vexation in the exercise field. While the human body and human movement are extraordinarily complex, and a person may possess some unique characteristics that require puzzle solving, I believe the vast majority of hamstring injuries are preventable through simple interventions…

The following videos and research explain the reasoning behind these simple solutions. First, I’m not actually trying to call anyone an idiot, just sparking interest hopefully. I am referring to allegedly “proper” sprint mechanics in which the pursuit of frontside dominance is often taken way too far.

Rather than super high knees, what we actually need during sprinting is high feet. There is actually such a thing as needing more backside mechanics.

In order to have high feet, we need flexibility in the rectus femoris muscle.

Now we need to talk about hamstring muscle characteristics. It is well known that strong muscles are less vulnerable to injury, but what about muscle length? Is it better to have flexible hamstrings? Some sport actions like hurdling and following through after a kick should feature hamstring flexibility. Regular sprint mechanics should NOT… but all athletes should still have long hamstrings. Why?

Greater muscle fascicle length (FL)…

  • decreases injury risk
  • increases contraction velocity.

If you know your muscle cell anatomy this should make sense, but let’s look at some large scale research.

Study: Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football: a prospective cohort study. 152 soccer players did pre-season hamstring testing, and then injuries during the season were recorded. Shout out to @ylmsportscience for the info-graphic. It shows clearly that short hamstring fascicles and weakness increased injury risk. FL under 10.56cm multiplied injury risk by 4.1.

Athletic performance is impacted by many variables, so you can’t expect just one to always yield the right correlation. But a few studies show greater FL in the quads and calves actually does correlate to faster 100m times, even within a population of sprinters. Side by side graphs below are from (1) Sprint performance is related to muscle fascicle length in male 100-m sprinters and (2) Relationship between sprint performance and muscle fascicle length in female sprinters.

The impact of FL is even more clear when comparing sprinters to distance runners or non-athletes. Study: Fascicle length of leg muscles is greater in sprinters than distance runners.

So we definitely want greater fascicle length, but here’s where it gets tricky. Fascicle length and flexibility/range of motion (ROM) are not the same thing. FL measures the contractile protein in the muscle, but there is much more to a muscle-tendon unit than just protein. Data shows that stretching clearly increases ROM dramatically but not always FL. Some training can increase FL, but maybe not ROM. So do we actually need hamstring flexibility? Or can we just train to increase FL? One study did show correlation between flexibility and lower injury rates, but this is not really the overall consensus of the research. This still leaves us with questions. Study: Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players: a prospective study.

It is clear that greater strength and greater fascicle length are good things. Research shows a variety of training can increase strength and fascicle length at a low level when compared to no training. But how do we get to a high level over time? We need to strength train with range of motion. There is a plethora of research evidence showing the superiority of strength training at long muscle length.

So we want to train the hamstrings at long length and increase strength and fascicle length over time. This can be achieved using hip hinges with long ROM. If you are starting out tight, can you simply strength train to get long ROM? In my experience, not with the hamstrings. Stretching them with hip hinges for 3-4 sets twice per week does not improve ROM, at least not very much within a couple months. Perhaps doing it every day would get the job done. But it’s more reasonable to stretch thoroughly every day, which typically improves ROM within days. Stretching is not in vogue in the exercise field, but it remains the best way to improve range of motion.

Along with long muscle length, the other key component to structural strength development is eccentric overload. I’m defining eccentric overload as a scenario when a muscle is contracting with maximum effort but being forced to lengthen by the resistance force/momentum. Many people believe this requires weight beyond what can be lifted (supramaximal), but actually this scenario can be created with regular weights by using momentum to add load. So hip hinges can provide the perfect structural strength stimulus for the hamstrings.

If you don’t believe eccentric overload happens with regular weights, try the following… Do no hamstring exercise for 10 days. Then put around 50% of your deadlift on the bar and do 3×10 fast, deep hip hinges like I do in the video below. The soreness in your hamstrings in the days following will be a strong indicator that some serious overload occurred.

Along with all the research there is plenty of experiential evidence to support this approach as well. A couple examples…

It´s Douglas here again, the Decathlete from Sweden. First of all i just want to say that the last video you send to me about stiff deadlifts have been a real success for me. I have had muscle strains in the hamstring like 10 times in my career before and it sucks but the last year has been No pain at all! So thank you so much for your videos!

Knee Flexion Strength

What about the Nordic hamstring curl? Do we need to train knee flexion strength? Consider separately neurological and structural characteristics.

Knee flexion does not drive athletic movement. It controls the lower leg during the swing phase of various activity. It’s low load, high velocity, submaximal effort movement. Slow, heavy knee flexion strength is not relevant neurologically. Training the brain to direct tons of neural drive into knee flexion is not meaningful.

Structurally speaking, the nordic curl (the best knee flexion exercise) can feature extremely high targeted hamstring effort and eccentric overload, two factors that create high muscle tension. What nordics lack compared to hip hinges is muscle length, which makes hip hinges a generally superior structural exercise. However two reasons why nordics are probably still worth doing…

  • The short head of the biceps femoris only crosses the knee, so it can only be trained by knee flexion.
  • Variety in loading probably has value structurally.

Also nordics have been shown to be highly effective compared to no direct hamstring work, so if you can’t do hip hinges please do these.

ACL Risk

When discussing hamstring training, another thing that needs to be mentioned is that the hamstrings are a critical muscle for ACL injury risk reduction. In research they have tested knee flexion and extension strength and found that the ratio correlates with ACL injury rates. The trap then is to conclude that you should focus on knee flexion exercises. ACL injuries occur during a PUSH into the ground, so in that moment being specifically stronger at the knee flexion pattern is not relevant. It’s fine to TEST hamstring strength with flexion, but your knee flexion should be strong because your hamstrings are strong in general, not because you exclusively trained that movement.