Updated: Feb 15
Hamstring injuries are extremely common, especially in sports involving running. In this article, we explain what puts you more at risk of a hamstring injury or re-injury and what you can do to avoid a hamstring strain. Remember, if you need more help with an injury, you're welcome to consult one of our physios online via video call.
Here’s how the story often goes… You spent time, weeks perhaps, being ‘good’ and resting your hamstring muscle strain while you went stir crazy, enviously watching your friends continue to play sport and run races. Your hamstring finally felt better, so you euphorically went back to sport / running, and a while later ... it went again! Aaargh! Infuriating! Now what!?
In this article:
Anatomy of the hamstring
The hamstrings are a big muscle group made up of the biceps femoris, the semimembranosus, and the semitendinosus. They all start at the sit bone (ischial tuberosity), at the bottom of the pelvis, and come down the back of the thigh and attach into the tibia, just below the knee. The biceps femoris attaches below the outside of the knee, and the semimembranosus and semitendinosus below the inside.
One of the interesting things about hamstrings is that they cross both the hip joint and the knee joint, so they can extend the hip (take the leg backwards) AND flex (bend) the knee.
When we run, one of the main jobs of the hamstrings during the swing phase of gait, i.e. when your foot is off the ground, is to lengthen in a controlled way (eccentrically) to manage at what speed and how far the powerful quadriceps muscles at the front of your thigh are straightening your leg.
There is one point, when at maximum stride length when sprinting, that the hamstrings are not only working hard eccentrically but also on a stretch; this is one of the most common times for the muscle to get injured.
As your leg starts to swing back and your foot makes contact with the ground, the hamstrings now produce a powerful concentric contraction (where the muscle shortens as it contracts) that helps to push you forward. The faster you run, the more forcefully your hamstrings contract.
A hamstring ‘strain’, ‘tear’, or ‘sprain’ all mean the same thing, and the severity of muscle injury is now graded 0–4 (previously 1–3) depending on how much of the muscle has been injured. The higher the grade, the longer it will take to rebuild the injured muscle and regain full strength.
So, now you have some background knowledge on how the hamstrings function, how does it apply to what you need to do to avoid injuring or re-injuring yours?
Hamstring strain risk factors you can manage
Let’s start with some of the ‘modifiable risk factors’ for hamstring strains or, in other words, stuff you can do something about to decrease the risk of it getting injured again.
We’ve already discussed how the hamstrings work eccentrically against the quadriceps when you run.
If there is a deficit in the endurance or the eccentric strength in the hamstrings, particularly in comparison to the quadriceps (the hamstrings : quads ratio), then there is an increased risk of hamstring muscle injury, as it is easily overwhelmed by the strength of the quadriceps.
How to fix this: Make sure that your rehab programme includes exercises that develop the eccentric hamstring action. This doesn’t mean that you should rush in and do Nordic curls right from the start. Eccentric contractions make the muscles work really hard, and you should first build your base strength with gentler exercises.
How far can you hop on one leg? Is it the same on both sides? If you’re a runner, you may wonder why hopping on one leg concerns you. This is just a way to test your hamstrings’ ability to create powerful concentric contractions.
A recent research review showed that returning to running/sport before recovery of full power can also increase your risk of hamstring muscle injury.
How to fix this: Include plyometric (hopping and jumping) exercises in the later stages of your rehab.
Core muscle control
Research has also shown that poor trunk muscle stabilisation and control while running can increase the risk of hamstring muscle injury. It is therefore important to address not just the hamstring itself, but any underlying biomechanical factors around the pelvis or spine that might need strengthening or improving.
How to fix this: Doing sit-ups and planks is not sufficient. You should include core exercises that require you to stabilise your pelvis while also moving your legs (this is what the core does when you run). An example of an early-stage exercise would be bridges with leg lifts.
High-speed running exposure / training error
It makes sense that if there is an increased mechanical risk in hamstring injury with sprinting, then the overall risk is increased the more you sprint.
There is also evidence that sudden increases in sprinting volumes in the past 7 to 14 days from what you are used to doing before also increase the risk of injury. However, a gradual increase or build up can be beneficial in conditioning the muscle to that load. Gradual conditioning may in fact contribute to a decreased risk of re-injuring your hamstring.
There is conflicting evidence about whether decreased recovery times between matches or races will increase the risk of hamstring injury – some studies say it does and others say it doesn’t; it probably depends on what your body is used to.
How to fix this: Plan your training carefully and avoid sudden increases in the frequency of your high intensity (fast running) sessions.
The evidence on whether tight hamstrings increase your risk of an initial hamstring injury is also not clear. However, poor flexibility in the hamstrings may increase the risk of recurrent strains.
How to fix this: Make sure that you regain your full range of motion after you’ve injured your hamstring. However, take your time, as you can actually re-injure your muscle if you stretch it too strongly early in your rehab. It’s often best to use eccentric exercises rather than passive stretches to regain the full range, as they strengthen the muscles as they lengthen them.
Hamstring strain risk factors you cannot control
Unfortunately, there are also a few ‘non-modifiable’ risk factors associated with hamstring muscle injury, i.e. things that increase the risk of injury that, well, you can’t really do much about.
Previous hamstring injury
When you’ve injured your hamstrings once, the risk of a recurring hamstring strain is 2.7 times higher than had you never injured it. This could be because of structural weakness and scar tissue being more vulnerable. That risk increases to 5 times higher if the hamstring was injured in the same competitive season; this probably accounts for people who try to return to sport too soon without completing a comprehensive rehab plan.
How to limit this risk: Make sure that you follow a carefully graded and progressive strength training plan to restore your injured hamstring’s strength, power, and flexibility. A typical plan will start with gentle, low intensity exercises that avoid taking the hamstrings into too much stretch.
As your injury recovers, these exercises should increase in intensity and include exercises that develop the eccentric muscle action as well as quick, powerful contractions. They should also strengthen the hamstrings through the full range it moves through when you run or play your sport.
It’s a sad fact of life that injury risk increases as we get older. This could be due to a decrease in tissue quality or perhaps an increase in overall exposure to load. Either way, age is not something any of us can do much about!
How to limit this risk: The good news is that research has shown that regular strength training can reduce your injury risk by up to 50% and also preserve your muscle mass and strength as you get older. You can read more about how to mitigate the effects of ageing on your running in this article.
Previous Anterior Cruciate Ligament (ACL) injury
Recent research has found that recurring hamstring strain risk is increased if there has been a previous ACL injury.
This may be due to a part of the hamstrings having been used for an ACL reconstruction graft. It could also be due to ongoing knee instability, which increases the load on the hamstrings.
How to limit this risk: The answer once more lies in the quality of your post ACL injury rehab. Take your time to build your function and strength, with particular focus on the hamstrings. Include lots of balancing work, as this can help to improve your knee control and stability.
How we can help
Our team of sports physiotherapists can help you with a full physio assessment to identify your modifiable risk factors and then put together a plan to address them, along with a graded strengthening and running conditioning build-up.
You're welcome to get in touch if you would like some guidance with this. Otherwise, good luck! Go and get this sorted and get back out there!
We're all UK Chartered Physiotherapists with Master’s Degrees related to Sports & Exercise Medicine. But at Sports Injury Physio we don't just value qualifications; all of us also have a wealth of experience working with athletes across a broad variety of sports, ranging from recreationally active people to professional athletes. You can meet the team here.
About the Author
Green B, Bourne MN, van Dyk N, et al. “Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport” British Journal of Sports Medicine 2020; 54:1081-1088
Brukner P, Nealon A, Morgan C, et al. “Recurrent hamstring muscle injury: applying the limited evidence in the professional football setting with a seven-point programme” British Journal of Sports Medicine 2014; 48: 929-938