The hamstring muscle is very important in sports such as football. Not only because this muscle is key to sprinting, but also because hamstring muscle injuries are the most frequent kind of injuries. For professional teams, these injuries also result in players being unavailable for competition over the course of many days. Nordic ham curls are a form of eccentric exercise that has become very popular, especially for its ability to reduce injury risk. However, there is little evidence that demonstrates their influence on improvements in speed.

To test this theory, a multidisciplinary group of researchers and coaches – including Marc Guitart, from F.C. Barcelona – carried out a research study which analysed the influence of this type of exercise when it was introduced into the training routine of different teams. The conclusions are somewhat counter-intuitive but clear: improvements in strength do not directly translate into improvements in sprinting ability. The article was published in the open access journal Plos One.

A wide-reaching and surprising study

The study analysed 50 reserve team players from three different teams, who were monitored for 15-17 weeks, almost half a season. One team followed their usual training program. The other two teams incorporated a progressive routine based on Nordic ham curls, which consist of “the player having their knees held in place on the ground by a teammate and letting themselves fall forward while keeping the body straight and controlled. This descent through a controlled knee extension assumes an eccentric activation of the hamstring musculature”, explains Guitart. The difference between the latter two teams was that one team had already incorporated these exercises during their previous season, so it was simply a continuation of an established routine.

After the experimental period, the ability to sprint over various distances was analysed, as well as the strength developed as a result of these eccentric exercises. It was found that the group that had incorporated the exercises for the first time did experience an increase in strength, both at an absolute level as well as relative to their body mass. However, improvements in speed for this group were not greater than those registered among the control group, which followed its usual routine. As for the team that had already started practising this type of exercise the previous season, strength increased relative to body mass, but not absolute strength. Furthermore, although this team progressed somewhat more in their ability to sprint over 20 meters, this improvement was not related to the gain in relative strength.

Conclusions, applications and future studies

“With this study our aim was to examine how the application of a Nordic-type strength exercise would affect football players’ sprinting ability”, summarizes Guitart, “and the conclusion is that there is no direct relationship”. These results contradict two previous studies that did find a link, but both of these studies were smaller in scope and were carried out over a shorter period of time.

Nevertheless “there is a lot of research that shows that this type of exercise is useful for the prevention of muscle injuries”, adds Guitart. This study revealed that players with previous experience implementing this kind of training barely improved their strength, surely because the load depends on their own body mass, which is practically invariable. Hence, the researchers propose using different stimuli over time, such as using rotational inertia devices, for example.

And the research doesn’t end there. “Now we are focusing on more multidisciplinary studies rather than on a specific exercise”, explains Guitart. “Above all, we are analysing how to control load and its complexity in terms of exercise, both in strength work as well as optimizing exercises on the pitch”, he concluded.

The Barça Innovation Hub team