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Sprinting versus strength training on risk factors for hamstring injury

If there is one argument that has dominated social media over the last 5-10 years, its the one that compares Nordics and other strength exercises to sprinting when the aim is to reduce hamstring injuries. Despite the call, “just do both”, the argument still persists. So we spoke to Anne Delextrat, who has investigated this in a recent study, and asked her six questions to give us more clarity.

Industry (social) media would lead us to believe that hamstring injuries continue to rise in football due to the lack of adoption of Nordics, players not sprinting enough and mechanics being suboptimal. Do you think it is as simple as these explanations? 

Those factors might play a role in the increased hamstring injury rates, however, I do not believe that it is as simple as this, no. You can throw in the increased intensity and competitiveness of matches at all levels, for example. This is very obvious in female players, too. The increased game intensity in the last decade has led to more injuries.

Fixtures congestion also increases injuries. If you look at Premier League schedules, they are sometimes insane, with players taking part in two or three matches some weeks. I haven’t looked at the data yet, but the last World Cup In November-December probably did not help either, with players coming back to their clubs and playing too early.

To comment specifically on the factors cited in the question, I think some of them might contribute to the increased injury rates, but we know that a lot more clubs do prevention exercises (Nordics, in particular) and coaches are more aware of the benefits of eccentric training. It depends on the level, of course, but I am not sure this is the main reason.

Sprinting is an interesting one, and could be a reason for more injuries if coaches are anxious about working on maximal speed in practice sessions to avoid injuries. It is now quite clear that you need to sprint in training to be able to safely sprint in a match, and some authors have referred to it as a vaccine. So yes, I think mentalities might need to change a bit to include more sprinting in practice sessions.

With regards to mechanics, it is a relatively newer area of research. Results show that mechanics can be corrected, in particular, an anterior tilt of the pelvis. Let’s see if it leads to fewer injuries!

The well known risk factors for hamstring injuries include eccentric strength, interlimb asymmetries and shorter fascicle length. What other risk factors do we often forget, and why are they important to consider?

Eccentric strength is a crucial one, of course, but people usually consider peak strength, which is not enough in my opinion. The angle at which peak eccentric strength is produced is important to consider, too. You want the angle of peak strength to occur as close as possible to extension, as that is where hamstrings tears occur. But the angle tends to be closer to knee flexion / further away from full knee extension in previously injured hamstrings. 

For the same reason, we should be looking at the value of the force (or torque) produced at knee angles close to extension.

The rate of force (or torque) development is another forgotten factor. The hamstrings need to contract quickly during different tasks to avoid excessive stress that leads to tears. Greater speed of contraction also helps protect the ACL from injuries.

Finally, a factor that I have been working on is hamstring muscular endurance. Footballers, and team sport players more generally, need to maintain a relatively good level of strength for the entirety of a match. We showed that the players with greater maximal strength experienced a larger decline in strength during a simulated match. This contributes to my belief that measuring peak strength is not enough in team sport players.

What benefits do Nordics give us that sprinting alone does not?

From our study as well as others, Nordics seem to be a greater stimulus for strength gain. We observed a 10% increase in strength in our sprint group and 20% increase in our Nordics group. It is a bit like other specific sport skills, in that you need to go the gym to get stronger as well as practising these skills.

There has been some criticism around Nordics for athletes who are less strong. The argument goes that they may not be able to perform the exercise all the way and “catch themselves” too early, hence not benefitting from the strength gains when the hamstrings are lengthened. However, I am not aware of any study that proved this, and we definitely did not show this in another study comparing Nordics and eccentric leg curls.

Reverse the question: What benefits does sprint training give us that performing Nordics alone can’t?

Sprinting increased the rate of torque development, while the Nordics did not. As mentioned earlier, being able to quickly produce strength is relevant to hamstring injuries.

Previously injured hamstrings are characterised by significantly lower rates of force development compared to non–injured limbs, and the fatigue caused by a football match is associated with a greater number of injuries. That combination led to greater decreases in RTD compared to other aspects, such as maximal voluntary strength. The reasons behind the benefits of sprinting are not well established yet, but we think that maybe the high speed contractions during sprinting play a role. We definitely need more studies on this topic

So, with all that said, should practitioners be prioritising Nordics or sprinting?

Both! Sprinting and Nordics are complementary. Each can improve specific risk factors, so using them in combination is ideal. Sprinting should definitely be used more in practice sessions, which may requite changing the coaches’ mentality.

In terms of when or for whom to use Nordics and sprinting, you can profile the strength-velocity relationship for each player on a team and identify their needs at different times in a season. The MySprint app lets you determine athletes’ theoretical maximal strength (F0) and theoretical maximal velocity (V0). These will help you set up training priorities. In particular, a low F0 is linked to subsequent hamstring injuries. To improve F0 and reduce that risk, loaded sprinting is the best option, as unloaded sprinting does not lead to improvements.

What are the biggest mistakes you see young practitioners/clinicians make and what advice would you give them to help?

Practitioners should screen players for risk factors in a fatigue state, as maximal strength does not seem to be as much of a factor in hamstring injuries as we once believed. Muscular endurance tests are good, too, but are more difficult for players to handle, as they are harder.

Using functional tests is probably the best way to identify asymmetries. With portable dual force plates, you can see power differences during jumps; and they are more affordable these days. The other common mistake is avoiding sprinting in practice sessions. While I completely understand where coaches are coming from, they can start with low volume sprint sessions to get more confident, and then progress and periodize these sessions as appropriate.

Article from SPORTSMITH By Anne Delextrat