Hamstring Injuries in Soccer

Muscular injuries are the most common type of injuries in football, with hamstring injuries representing 12% of all injuries recorded. (Ekstrand et al., 2011). The time missed from these injuries may cost teams trophies and promotions and may result in the loss of a player's contract and starting places. This article aims to review the current literature surrounding hamstrings injuries in professional football and suggest measures to mitigate the risk of future injuries and re-injuries.

Epidemiology

Ekstrand et al. (2016) found the total occurrence of hamstrings injures is 1.2 per 1000 exposure hours during a 13-year longitudinal analysis. When the above is separated into match and training, a significant change can be seen with 4.77 and 0.51 injuries per 1000 exposure hours being recorded. The average time missed is 19.7 hours with the authors noting an annual average increase of 4%. Earlier work from Ekstrand et al. (2011) estimated over 80 days of football activities will be missed in a squad of 25 players. Additionally, re-occurrences within 2 months represented 13% of total injuries, suggesting currenting rehabilitation practices are ineffective.

Mechanisms

66% of hamstring injuries in Ekstrand et al. (2015) were designated as acute onset, with the remainder categorised as chronic. Askling, Malliaropoulos and Karlsson (2012) identified two different types of hamstring injuries; a sprint-based injury and a stretching-based injury, where the sprint based being the most common in football (Woods et al, 2004). However, the exact moment in the gait cycle is the source of debate as it is very difficult to measure muscle fibre strain, ground reaction force etc in vivo. Acute muscular injuries are thought to occur due to excessive lengthening and activation of the contractile elements (Leiber & Friden, 2002). This led researchers to believe that terminal swing and or early stance is mostly likely the specific instance the damage occurs (Yu, et al., 2008; Schache, Dorn, Blanch, Brown, & Pandy, 2012, 2013 ) due to the high levels of action activation and long muscles lengths. Yu et al. (2008) found that peak eccentric contractions speeds were significantly higher during late swing phase than late stance phase with no differences found in musculo-tendon lengths. The long head of biceps femoris undergoes the biggest change in musculo-tendinous unit (MTU) when compared with the semitendinosus and semimembranosus (Chumanov, Heiderscheit, & Thelen, 2007; Schache et al., 2012). This also coincides with evidence suggesting the Bicep Femoris is the most injured hamstring muscle (Peterson & Holmich, 2005; Askling, Tengvar, Saartok & Thorstensson, 2007). Additionally, changes in MTU length also suggest that the hamstring group experience a stretch shortening cycle with lengthening occurring as the shank extends and shortening occurring just before stance. Summarising the above, it appears long head bicep femoris injuries result from tissue failure at the MTU complex (Askling et al., 2007) during late swing phase as hamstring eccentrically controls hip and knee extension at fast velocities.

Risk Factors

Injury is the biggest predictor of future injury and the hamstrings are no exception (Engebresten et al., 2010). Previous injury may affect the length-tension relationship, moving the peak to left and increasing the descending arm of the curve. As hamstring injuries occur at long lengths, this may increase the likelihood of a re-injury (Bosch & Klomp, 2005). Other risk factors include age and agonist-antagonist ratios, although further research is needed to elucidate which combination of contraction modes and angular velocities may be useful. (Freckelton & Pizzari, 2013). Extrinsic factors include inadequate warm-ups and increased fatigue, all of which can be modified by the practitioner.

Injury Prevention Programs

Injury prevention exercise should be specific to the mechanism of injury in order to be effective (Peterson & Holmich, 2005). Verkoshankeys (1986) outlined his dynamic correspondence criteria in which he suggests a method for assessing an exercise’s transferability to a target exercise. A full review of the Dynamic Correspondence criteria is not appropriate here, however high-speed running meets the most criteria and would therefore have the greatest transfer to preventing sprint-based hamstring injuries. Anecdotally, football teams track high speed running (HSR) metres using GPS system for return to play protocols, however this empirical evidence from (Duhig et al., 2016; Malone et al., 2018) suggest a spike in HSR metres over that of their 2-year average, puts an athlete at risk of injury. Therefore, the gradual accrual of HSR should be targeted to minimise injury risk in soccer players. Tempo runs are a conditioning method where distances are covered at submaximal speeds but with maximal velocity mechanics. This provides an opportunity to fine tune hamstring SSC performance and manipulate maximal velocity mechanics in a controlled environment.

Eccentric exercises, in particular the Nordic Hamstring exercise has been shown to be effective in reducing hamstring injuries (van de horst, Smits, Peterson, Goehart, & Backx, 2015). Supramaximal eccentric exercise promotes unique architectural adaptations not seen elsewhere in resistance training such as increase in fascicle length and a reduction in pennation angle, amongst strength gains at long muscle lengths (Blazevich, Cannavan, Coleman & Horne, 2007; Vogt & Hoppler, 2012). As previously noted, optimal length- tension relationship of the hamstrings is a risk factor for injury and adaptations to Nordics may move peak force production to longer muscle lengths hence reducing injury risk. However, this exercise misses velocity/time criteria of dynamic correspondence and therefore has less transfer. A modification of the Nordic Curl such as partner push, fast drop and catch, or med ball throw and catch, adds a faster eccentric element and thus higher correspondence, possibly leading to a decreased injury risk. Care should be taken when implementing these modified Nordic exercises.

The hamstrings perform other roles such as stiffening the knee joint at ground contact and hip extension during stance, that should not be forgotten. Increasing the maximum strength of hamstrings during hip extension may improve propulsion at ground contact and reduce injury risk. As such, high load closed chain hip extension exercises such heavy as Romanian Dead Lifts’s should also be incorporated into the program alongside stretch shortening cycles (SSC) activities and eccentric knee flexion exercises.

Below is a table demonstrating different types of exercises and possible variations that meets different aspects of Dynamic Correspondence for preventing sprint-based hamstring injuries.

In summary, hamstring injuries are highly prevalent in football, where the time missed from training and reinjury rate is also high. Risk factors include previous injury, agonist-antagonist strength, hamstring range of motion, inadequate warmups and in-appropriate training loads. The main mechanism of hamstring injury in football is sprinting, usually involving a tissue failure of musculotendinous interface of the Bicep Femoris Long Head. Rehabilitation and prevention should consider the eccentric and SSC nature of hamstring during sprinting, choosing exercises and progressions that gradually improve these capacities.

References:

Askling, C. M., Tengvar, M., Saartok, T., & Thorstensson, A. (2007). Acute first-time hamstring strains during high-speed running: a longitudinal study including clinical and magnetic resonance imaging findings. The American journal of sports medicine, 35(2), 197-206.

Askling, C. M., Malliaropoulos, N., & Karlsson, J. (2012). High-speed running type or stretching-type of hamstring injuries makes a difference to treatment and prognosis.

Blazevich, A. J., Cannavan, D., Coleman, D. R., & Horne, S. (2007). Influence of concentric and eccentric resistance training on architectural adaptation in human quadriceps muscles. Journal of Applied Physiology, 103(5), 1565-1575.

Bosch, F., & Klomp, R. (2005). Running: Biomechanics and exercise physiology in practice. Elsevier Churchill Livingstone.

Chumanov, E. S., Heiderscheit, B. C., & Thelen, D. G. (2007). The effect of speed and influence of individual muscles on hamstring mechanics during the swing phase of sprinting. Journal of biomechanics, 40(16), 3555-3562.

Duhig, S., Shield, A. J., Opar, D., Gabbett, T. J., Ferguson, C., & Williams, M. (2016). Effect of high-speed running on hamstring strain injury risk. Br J Sports Med, 50(24), 1536-1540.

Ekstrand, J., Hägglund, M., & Waldén, M. (2011). Injury incidence and injury patterns in professional football: the UEFA injury study. British journal of sports medicine, 45(7), 553-558.

Ekstrand, J., Waldén, M., & Hägglund, M. (2016). Hamstring injuries have increased by 4% annually in men's professional football, since 2001: a 13-year longitudinal analysis of the UEFA Elite Club injury study. Br J Sports Med, 50(12), 731-737.

Engebretsen, A. H., Myklebust, G., Holme, I., Engebretsen, L., & Bahr, R. (2010). Intrinsic risk factors for hamstring injuries among male soccer players: a prospective cohort study. The American journal of sports medicine, 38(6), 1147-1153.

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Malone, S., Owen, A., Mendes, B., Hughes, B., Collins, K., & Gabbett, T. J. (2018). High-speed running and sprinting as an injury risk factor in soccer: Can well-developed physical qualities reduce the risk?. Journal of science and medicine in sport, 21(3), 257-262.

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Schache, A. G., Dorn, T. W., Wrigley, T. V., Brown, N. A., & Pandy, M. G. (2013). Stretch and activation of the human biarticular hamstrings across a range of running speeds. European journal of applied physiology, 113(11), 2813-2828.

van der Horst, N., Smits, D. W., Petersen, J., Goedhart, E. A., & Backx, F. J. (2015). The preventive effect of the nordic hamstring exercise on hamstring injuries in amateur soccer players: a randomized controlled trial. The American journal of sports medicine, 43(6), 1316-1323.

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Yu, B., Queen, R. M., Abbey, A. N., Liu, Y., Moorman, C. T., & Garrett, W. E. (2008). Hamstring muscle kinematics and activation during overground sprinting. Journal of biomechanics, 41(15), 3121-3126.