Hamstring Strains in Soccer

Once clinicians establish the extent of HSIs, they must identify the risk factors and injury mechanisms to implement preventive programs. They can divide the risk factors into two categories: primary and recurrent factors. The primary risk factors are then subdivided into non-modifiable and modifiable⁽⁵⁾. Non-modifiable primary injury risk factors include age, previous injury history, ethnicity, competition level, and the latest periods of matches. The modifiable risk factors are the player’s hamstring muscle strength imbalance ratio and the player’s health education^(2,6).

“The incidence of hamstring strain injuries continues to rise…”

Injury Risks

Chronological age impacts the likelihood of sustaining an HSI⁽⁶⁾. Starting at age twenty, the likelihood of injury increases by 1.3 times every year, regardless of previous injury history. Previous non-hamstring-related injuries are also a risk factor for a primary HSI, with links to anterior cruciate ligament reconstruction and a history of osteitis pubis⁽²⁾. Furthermore, players of African ethnicity have an increased anterior pelvic tilt when compared to their caucasian compatriots, increasing their primary injury risk^(2,7). Finally, the level of competition and the latest periods of soccer matches increase the primary HSI risk. This is due to the increased physical demands and match exposure time with decreased training and recovery. For example, 50% of all the match HSI occur during the last 15 minutes of each half^(2,3,8).

The hamstring-to-quadriceps ratio indicates a player’s injury risk. Unbalanced ratios mean the quadriceps will overpower the hamstrings and result in injury⁽⁹⁾. Traditionally, a ratio of 0.6 to 1 is ideal. However, some clinicians argue that a 1:1 ratio is preferential due to the hamstring’s eccentric strength requirements when providing knee-joint stability^(2,10). Player health education is essential when looking to promote internal health control and pain awareness, as players predisposed to HSI may lack health literacy, ignore physical, and psychological consequences of persisting through pain⁽⁶⁾.

A history of injury increases the risk of sustaining another injury. For example, players with a previous HSI have 2-3 times the risk of sustaining another injury⁽¹¹⁾. Clinicians consider this when aiming to minimize injury risks. Inadequate rehabilitation and change in optimal muscle length are modifiable risk factors. If athletes return to sports prematurely, they are at risk of reinjury. Therefore, clinicians must ensure that they are appropriately conditioned to meet the demands of their competition level and consider changes in the length-tension relationship before clearing athletes to return⁽²⁾.

Injury Mechanism

Running/sprinting is the most common mechanism of HSI (61%), especially during matches (see table 2). The hamstrings are most vulnerable during the terminal swing phase, as they work to eccentrically decelerate the swinging tibia and control knee extension as the player shifts into foot strike^(3,8).

Table 2: Hamstring injury characteristics⁽³⁾

Injury is an Opportunity

Once an athlete sustains an HSI, rehabilitation must begin immediately to ensure the player’s timely return to play. Clinicians can use several interventions, but their implementation must be carefully considered and individualized to minimize setbacks and reinjury after clearance, while maintaining performance at the same level. The injury-healing process is an opportunity to review the athlete in their entirety⁽¹²⁾.

1. The Askling L-Protocol (see table 3)
   The Askling L-protocol is more effective than conventional exercises. It comprises exercises that load the hamstrings during extensive lengthening, mainly during eccentric muscle actions, and shorten the average time to return to play from 51 to 28 days⁽¹³⁾.
2. The Sherry and Best Protocol
   The Sherry and Best Protocol consists of progressive agility and trunk stabilization exercises and is more effective than programs that focus on isolated hamstring stretching and strengthening, with the significantly lower rate of reinjury being attributed to improved neuromuscular control and limited end range tension of the hamstrings⁽¹⁴⁾.

Table 3: The Askling L-Protocol

Progressive running is an incredibly important intervention in a player’s gradual return to play due to its fundamental role in soccer performance (see figure 2)⁽¹⁵⁾. A 3-stage protocol begins once a player can walk with minimal pain, progressing from 25% of maximal speed to 50% of maximal speed, pain-free. Once this is achieved, they must shift into stage two, which involves building up to 80% of maximum speed, pain-free. The final stage sees the player progress from 80% to 100% maximal speed. Once this is completed, practitioners should individualize the running exposure based on the player’s running profile, positional requirements, and tactical model demands⁽¹⁵⁾.

“Once an athlete sustains an HSI, rehabilitation must begin immediately…”

The first cone to the second cone is a gradual build-up; the second to the third is the maximum speed for each range, and the third to the fourth is the deceleration phase.

Prevention 

Injury prevention programs can decrease the rate of HSIs. The FIFA 11+ decreases the risk of HSI. However, compliance determines the program’s success⁽¹⁶⁾. The program should be completed 2 – 3 times/week throughout the season, in conjunction with other warm-ups that allow for greater variety and are more soccer-specific to improve compliance, reduce staleness, and maximize injury prevention benefits^(16,17).

Nordic hamstring exercises improve hamstring eccentric strength, enhancing overall knee health and reducing HSI rates⁽¹⁸⁾. It is essential to note that these exercises are complex, and beginners should start with smaller ranges of motion (ROM), progress to assisted NHE, and ultimately, achieve unassisted NHE with full ROM (see table 4).

Table 4: Nordic hamstring exercise progressions⁽¹⁸⁾

Practitioners must also consider high-speed running exposure as a protective strategy from HSI. For example, Portuguese researchers have demonstrated that introducing near-maximal sprinting speed (MSS) on matchday (MD) -2 is protective against HSIs⁽¹⁹⁾. Exposure to near-MSS is crucial during training and rehabilitation, as players may not be exposed to sufficiently high speeds during the training week. Furthermore, eccentric strengthening programs do not recruit higher levels of muscle recruitment. From a practical perspective, players need to sprint over at least a 30m distance to reach near-to-MSS. Exposures should take place on MD-2 and must be greater than 95% effort. Practitioners must adjust the training week to place near-MSS exposures on MD-2, ensuring that players do not train on MD-2 with residual fatigue, which would put them at risk of injury.

Conclusion

The incidence of hamstring strain injuries continues to rise, and clinicians must be aware of the risk factors and available preventive strategies. Once an athlete enters the rehabilitation process, clinicians must consider returning them with robust physical qualities to minimize the risk of reinjury. Furthermore, when administered in a structured and periodized manner in response to a well-conducted injury audit, player health education can reduce players’ internal risk and, therefore, their injury predisposition.

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