The Importance of Eccentric Hamstring Strength in Soccer Players
Hamstring and knee injuries are some of the most common injuries to plague soccer players. According to statistics compiled by PhysioRoom.com, a website dedicated to tracking injuries in the English Premier League (EPL), hamstring injuries accounted for 150 incidents while knee injuries numbered 119 during the 2016/2017 season alone (1). Figure 1 displays the top six injuries by type experienced in the EPL.
While it was hard to determine the amount of games each individual player missed due to injuries which occurred at the hamstring or knee alone, it can be assumed that return to play lasted anywhere from a few weeks, for the most minor of strains, to six to nine months. Injuries which lasted fourteen days or more were compiled into Figure 2, and broken down by EPL club. Due to the expected return to play timelines previously established and combined days missed from Figure 1, it can be deduced that a fair number of injuries in Figure 2 were knee or hamstring related.
Serious knee and hamstring injuries represent a problem not only for the player or manager, but also the club itself, due to the large salary amounts commanded by professional players. This monetary issue is clearly defined by the staggering amount spent by clubs in the EPL on the injury wage bill for the 2016/17 season (see Figure 3).
Since it is apparent there is a lot of players suffering from hamstring and knee injuries within the professional football (soccer) ranks, let?s cover some ways to potentially mitigate the risks of obtaining these injuries.
Risk Factor Research
Due to the demand for players to remain injury free, much research has been dedicated to discovering how to prevent hamstring and knee injuries. A 2014 study published in the British Journal of Sports Medicine and conducted by Alan McCall, Ph.D, examined risk factors, testing and preventative strategies for non-contact injuries at the professional football (soccer) level. The study had professional teams rank the perceived importance of non-contact injury risk factors in order of most important to least important (2).1st: Previous injury
1st: Previous injury
3rd: Muscle imbalance
5th: Movement efficiency
While previous injury is an unmanageable risk factor, the other four factors can (and should) be improved to minimize injury risk. Some might argue that fatigue is not able to be measured objectively and therefore is not a valid inclusion into the perceived risk factors. This is a valid observation partly due to the difficulty of precisely defining fatigue itself, however, a study conducted by Bengtsson et al. objectively found that muscle injury rates in professional football increase with fixture congestion (3). This increased injury rate directly correlates to the theory of fatigue as a risk factor. Furthermore, McCall et al. assert that fatigue and fitness can be considered to be interrelated and therefore by improving overall fitness, we as Strength and Conditioning (S&C) coaches, can minimize fatigue (2).
Whereas EPL teams ranked muscle imbalance as the third highest perceived risk factor, other studies have proposed muscle-strength deficiency as the main risk factor (4-6).? In the case of hamstring and knee injuries, the muscle-strength deficiency is referring to the strength ratio of the quadriceps versus the hamstrings. A study conducted by the University of Copenhagen found that ?The majority of hamstring injuries in soccer occur while players are running or sprinting and these injuries seem to occur in the late swing phase, where the hamstring muscles generate tension while lengthening (eccentric contraction) to decelerate knee extension? (7). Furthermore, ?It is suggested that eccentric resistance exercise may prevent injury by improving the muscles? ability to absorb more energy before failing? (8).
These findings demonstrate the necessity for hamstring strength, but how can coaches, sports medicine staff and even players themselves improve eccentric hamstring strength?
Implementation and Findings
The evidence is increasingly telling us that the answer is Eccentric Overload Training. There are multiple variations of exercises to eccentrically overload the hamstrings, however, the Nordic Hamstring Exercise (NHE) may be the best suited to training soccer players within a team setting. This is due to the fact that this exercise requires no equipment and can be conducted on the pitch. For those unfamiliar with the NHE see Figure 4, below, for an explanation and associated statistics regarding injury prevention (9).
The statistics in Figure 4 are derived from the previously mentioned study by the University of Copenhagen and conducted by Petersen et al., which assessed 461 players in an intervention group out of 942 professional and amateur soccer players (7). The intervention group was assigned to a 10 week NHE program in addition to the regular season training. The study found that the training program reduced the injury rate of new injuries by more than 60%. Even more impressive, however, was the highly effective reduction in the rate of recurrent injuries, which was reduced by approximately 85% (7).
Figures and findings such as these should encourage soccer coaches, S&C coaches, and sports medicine staff to utilize similar programs which can provide injury prevention capabilities. It should be noted that volume should be minimized due to the ability of eccentric training to elicit a hypertrophy response. A recommended team training protocol should be similar to the program used for the 10 week NHE intervention group, which can be seen below in Figure 5.
With the overwhelming amount of evidence now available on the benefits of eccentric training to prevent hamstring and knee injuries, there is no reason for a team to not implement a similar type of ?prehab? training. As the aforementioned statistics in Figures 1-3 demonstrate, knee and hamstring injuries contribute to a significant amount of time and money lost. With such a high reward, in terms of decrease in the risk of injury/re-injury, and the ability to easily incorporate eccentric training into a program; what is there to lose?
- McCall A, Carling C, Nedelec M, et al Risk factors, testing and preventative strategies for non-contact injuries in professional football: current perceptions and practices of 44 teams from various premier leagues. Br J Sports Med Published Online First: 16 May 2014. doi: 10.1136/bjsports-2014-093439
- Bengtsson, H., Ekstrand, J., & H?gglund, M. (2013). Muscle injury rates in professional football increase with fixture congestion: An 11-year follow-up of the UEFA champions league injury study. British Journal of Sports Medicine, 47(12), 743. doi:http://dx.doi.org/10.1136/
- Rahnama N, Reilly T, Les A, et al. Muscle fatigue induced by exercise simulating the work rate of competitive soccer. J Sports Sci. 2003;21:933?942. PubMed doi:10.1080/
- Greig M. The influence of soccer-specific fatigue on peak isokinetic torque production of the knee flexors and extensors. Am J Sports Med. 2008;36:1403?1409. PubMed doi:10.1177/0363546508314413
- Croisier JL, Ganteaum S, Binet J, Genty M, Ferret JM. Strength imbalances and prevention of hamstring injury in professional soccer players a prospective study. Am J Sports Med. 2008;36:1469?1475. PubMed doi:10.1177/0363546508316764
- Jesper Petersen, MD, PhD, Kristian Thorborg, PT, PhD, Michael Bachmann Nielsen, MD, PhD, DMSc, Esben Budtz-J?rgensen, MSc, PhD, Per H?lmich, MD. Preventive Effect of Eccentric Training on Acute Hamstring Injuries in Men?s Soccer The American Journal of Sports Medicine. 2011 Vol 39, Issue 11, pp. 2296 – 2303 doi:10.1177/0363546511419277
- LaStayo PC, Woolf JM, Lewek MD, et al. Eccentric muscle contractions: their contribution to injury, prevention, rehabilitation, and sport. J Orthop Sports Phys Ther 2003;33:557?71
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