Hamstring injuries are some of the most common reasons runners miss out on training and competition. If you’ve ever felt a sudden twinge in the back of your leg, you know how frustrating and painful these injuries can be.
Recovering from a hamstring strain can take weeks or even months, and re-injury rates are notoriously high. This is why injury prevention is critical, especially for runners, who rely heavily on their hamstrings for performance.
One of the most effective ways to reduce the risk of hamstring injuries? Eccentric training. Specifically, exercises like the Nordic hamstring curl (NHC) have been shown to improve both the strength and flexibility of hamstrings, significantly lowering the risk of injury.
But what makes eccentric exercises so effective, and how can they fit into your training routine? Let’s take a closer look at the science behind them and how they can keep you running strong.
The Science of Eccentric Training
Eccentric exercises focus on the lengthening phase of muscle contraction. Think of it as the “lowering” part of a movement. For example, during a bicep curl, the eccentric phase is when you slowly lower the weight back down. For your hamstrings, this type of exercise involves resisting the force as your legs extend, which places controlled stress on the muscles.
Research has shown that this stress induces positive adaptations in the hamstring muscles, making them more resilient to injury. A study conducted on eccentric training with the Nordic hamstring curl over a 9-week period found significant improvements in hamstring muscle structure and function. After the training program, participants saw the following changes:
- Increased muscle fascicle length: The hamstring muscles grew longer, allowing them to handle greater stretches without becoming injured.
- Higher muscle strength: Participants’ knee flexion strength increased by an impressive 40%.
- Increased muscle volume: The overall size of the hamstring muscles grew by about 8%.
These changes are particularly important for runners because they help distribute the load more evenly across the muscle during activities like running and sprinting. This means less strain on individual muscle fibers, reducing the risk of overstretching and injury.
Why Hamstring Injuries Happen
Hamstring injuries typically occur when the muscle is overstretched, often during high-speed running or acceleration. Interestingly, research on hamstring mechanics during running shows that the risk is higher during accelerative running compared to constant-speed running. In accelerative running, the hamstrings are stretched more and at a faster rate, increasing the likelihood of injury. This is particularly true when athletes are accelerating from lower speeds—exactly the kind of situation that happens in sprints or bursts of speed during a race.
During these moments, the hamstrings are under a significant amount of load, trying to both lengthen and generate power at the same time. This is where eccentric training can play a key role. By strengthening the hamstrings and increasing their flexibility, eccentric exercises help the muscle withstand these high-risk situations, spreading the load across more of the muscle and reducing the likelihood of strain.
What Happens During Eccentric Training?
When you perform exercises like the Nordic hamstring curl, you’re essentially training your muscles to get stronger during the lengthening phase. This leads to some fascinating adaptations in the muscle structure. After several weeks of training, your hamstring muscle fibers get longer by adding more sarcomeres (the basic units of muscle fibers) in series. The addition of sarcomeres helps the muscle handle more stretch with less strain on each individual fiber.
In the Nordic hamstring curl, you start by kneeling on a soft surface, with your ankles secured (either by a partner or hooked under something stable). Then, you lower your torso slowly toward the ground, using your hamstrings to resist gravity as much as possible. This eccentric action stretches the hamstrings under load, stimulating those crucial adaptations.
One study found that after nine weeks of this training, muscle fascicle length increased by 19% in the central part of the hamstring and by 33% in the distal part of the muscle. Not only that, but participants experienced a 25-49% increase in the number of sarcomeres, which further reduced the risk of injury. The longer the muscle, the more resistant it becomes to being overstretched during high-speed running.
Why Should Runners Care?
If you’re a runner, particularly a sprinter or a long-distance runner who regularly pushes their speed, hamstring health is essential to your performance. Injuries can sideline you for weeks, and the recovery process can be slow and frustrating. Even worse, re-injury is common because many athletes don’t fully restore their hamstring strength and flexibility before returning to training.
Eccentric training helps prevent this by targeting the exact areas where hamstrings are vulnerable. The Nordic hamstring curl is a simple, yet highly effective exercise that directly strengthens the muscle in a way that mimics real-world running conditions. By increasing the muscle’s capacity to handle stress and stretching, you protect yourself from the sharp, sudden strains that can occur during speed work or sprinting.
But eccentric training doesn’t just benefit sprinters. Distance runners also stand to gain from improved hamstring resilience. Many long-distance runners suffer from hamstring issues caused by repetitive strain over long training periods. Strengthening the muscle through eccentric training can help it recover more effectively from repeated use and prevent chronic issues from developing.
How to Add Eccentric Training to Your Routine
Incorporating eccentric exercises into your weekly training plan is easy and doesn’t require a lot of equipment. Start with Nordic hamstring curls two to three times per week. Here’s how to do them:
- Kneel on a soft surface and secure your ankles (you can use a partner to hold them down, or hook your feet under something sturdy).
- Keep your body straight, from your head to your knees.
- Slowly lower your torso toward the ground, resisting gravity as much as possible with your hamstrings.
- Catch yourself with your hands if necessary, and push yourself back up to the starting position.
Start with 2-3 sets of 6-8 repetitions. As you get stronger, you can challenge yourself to rely less on your hands and more on your hamstrings for control.
Consistency Is Key
Like any training method, the key to success with eccentric training is consistency. While studies show that even short training programs of a few weeks can lead to muscle adaptations, those improvements can quickly be lost if the training stops. One study found that just three weeks after stopping eccentric training, muscle fascicle length decreased by 12-16%, and some of the benefits were lost. So, keep eccentric work as a regular part of your routine to maintain strong, resilient hamstrings.
Eccentric hamstring training, particularly through exercises like Nordic hamstring curls, can be a game-changer for runners and athletes. It strengthens and lengthens the muscles, improving their ability to handle high-speed running and accelerations—situations that are notorious for causing injuries. By making this a consistent part of your training, you’ll reduce your risk of injury, improve your performance, and keep running strong.
References
Max H. Andrews et al., Multiscale hamstring muscle adaptations following 9 weeks of eccentric training, Journal of Sport and Health Science (2024), https://doi.org/10.1016/j.jshs.2024.100996
Gurchiek, R. D., Teplin, Z., Falisse, A., Hicks, J. L., & Delp, S. L. (2024). Hamstrings Are Stretched More and Faster during Accelerative Running Compared to Speed-Matched Constant Speed Running. https://doi.org/10.1101/2024.03.25.586659
