Nordic curls & injury prevention.

Hamstring injuries are common in ball sports with explosive running patterns. But can also occur in sports that require maximum effort such as powerlifting. A hamstring injury can also occur in sports that require a lot of flexibility such as gymnastics or taekwondo. Symptoms of a hamstring injury can vary. There is often a sharp pain immediately or shortly after the moment of onset. In some cases, there is a snapping sensation. The pain is almost always well localized and a bruise may appear within a few days. With both small tears and larger injuries, stretching the hamstring will trigger the symptoms. Hamstring injuries generally recover well. The only thing we often see is that the chances of another hamstring injury are high. Within two months, 12-25% re-injure the hamstring. The biggest risk factor for a hamstring injury is a past hamstring injury. So it is important that you know how to prevent re-injury symptoms! In this blog, we are going to explain to you what a hamstring injury is and what your options are regarding injury prevention.

Anatomy of the hamstrings

The hamstrings is a group of muscles at the back of your thigh. This muscle group runs from your ischial tubercle to both the inside and outside of your knee. The hamstrings is a bi-articular muscle group. This means that the muscle runs across two different joints. In this case, across the hip and the knee. Because the function of the hamstrings runs over 2 joints, the risk of injury is also greater. The hamstring's function is to bend the knee and extend the hip. Under fatigue or while delivering maximum force, the control of the muscles can sometimes go wrong and the pulling forces on the muscle are too great.

The Latin names for the hamstrings are:

  • musculus semitendinosis
  • musculus semimembranosis
  • musculus biceps femoris

 

 Recovery from groin pain
Different types
hamstring injuries 

A hamstring injury is one of the most common non-contact injuries in various sports. We divide this injury into two different types. This classification is made based on the mechanism of occurrence:  

In type 1, there is an explosive moment such as in a sprint. The forces on the muscle fibers of the hamstring are too great and damage occurs. 

Besides sprinting, there are other examples where a type 1 hamstring injury can occur think of: jumping, hurdling in athletics or a deadlift in powerlifting. In sprinting, we see that this injury often occurs in the moment when the foot is just about to hit the ground. At this stage in the sprint pattern, the forces are greatest. The muscle is now firing at maximum but must also brake eccentrically to maintain good control of the knee and position of the foot on the ground.

  • 12-16% of all injuries in professional soccer are hamstring injuries
  •  75% of the cases involve injury to the biceps femoris

A type 2 hamstring injury are injuries where there is a lot of stretch on the muscle, often in gymnasts or dancers. This happens when the hip has to flex to its maximum extent and the muscle stretches excessively. In most cases, this is a less painful injury but the recovery time is often longer because the injury is in the upper part of the hamstring toward the tendon. This type usually involves injury to the semimembranosus.

We know that strength training can reduce the risk of injury. Especially getting stronger in the eccentric phase is important when you want to prevent hamstring injuries. Thus, stronger hamstrings reduce injury risk(1). Eccentric training also creates anatomically longer muscles(2). Here we no longer mean that you actually get longer muscles. This is probably why you can become more limber from controlled strength training, though. A muscle bundle is defined as a bundle of multiple muscle fibers together. Athletes with longer muscle bundles are less likely to suffer a hamstring injury. 

A study conducted in September 2021 in recreational athletes shows that sarcomeres lengthen after 3 weeks of training with the nordic hamstring curl. This lengthening in sarcomere length is most likely responsible for the longer muscle length. The exact explanation is still unclear(3). 

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Training for less risk of hamstring injury

You can train your hamstring in two different ways:  

  1. Knee flexion 
  2. Hip extension 

An example of a hamstring exercise in knee flexion is the nordic curl. The nordic curl reduces the risk of a hamstring injury by an average of 50%(4). You also see this exercise more and more on the training fields for example in the preparation of a season. With this exercise you train mainly the eccentric phase of the hamstring. You deliver power while the muscle lengthens. 

An example of a hamstring exercise more focused on hip extension is the romanian deadlift(RDL). It is much easier to focus on eccentric phase with the Nordic curl than with an RDL. It is technically an easy exercise. You can reap the benefits of the nordic curl over the RDL more quickly for this reason.

But the RDL has two strengths when compared to the nordic curl: 

  1. More emphasis on biceps femoris 
  2. More stretch on the hamstrings than with the nordic curl

Let it be precisely the biceps femoris that is most prone to a muscle injury. It is then useful to do an exercise where it is also best trained. So when you can train a muscle in a wide range so fully by length we see changes in muscle length(only in the muscle bundle). With that in mind it makes sense to see if an RDL can be as effective, or perhaps more effective compared to nordic curls.

Conclusion

For optimal results, it is good to include both variations in your program. A Nordic curl is a great exercise to train strength in the hamstrings. When you only do Nordic curls you miss exercises where the hamstrings are trained in a (fully) stretched position. An RDL where full-length muscles are loaded is then a good choice. If you were to get much stronger in your RDL, this is also probably more effective than just a nordic curl. But really building in weight for an RDL takes time. Consider grip strength and the more difficult technical execution of a compound exercise. Like a hyperextension, for example, the Nordic curl is an easy-to-execute exercise with a fast learning curve. This makes it that you progress faster in strength in the hamstrings. Therefore, keep doing Nordic curls but in the meantime, become a king in the RDL. This increase in strength in the hamstrings can make an injury less likely to occur. Unfortunately, truly preventing injury is never possible. We are dealing with too many factors that can potentially contribute to the occurrence of an injury. No guarantees! Increasing the load capacity in the hamstrings through strength training is certainly a good start! You don't sprint with two legs at the same time. Therefore, it is also wise to introduce unilateral exercises into your program. That is, with one leg. In addition to the standard exercise, do a unilateral form of the RDL and possibly the Nordic Curl. If you are not ready for this yet, because these exercises are heavy, use a Roman Chair or a hyper extension. Good luck!

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