An injury is an incident that occurs during a scheduled game, competition or practice causing an athlete to miss the next game, competition or training practice. One of the most common injuries in sport is the hamstring injury. This is observed in sports that involve sprinting or jumping. One of the main issues with this injury is the reoccurrence of injury. Hamstring injuries are frustrating for athletes, but also for coaches and medical staff, as its a persistent, slow healing injury with a high re-injury rate. (2) 12-16% of all injuries in English football are hamstring injuries, with a reoccurrence rate of 12-31%. Each club has an average of 5-6 hamstring injuries each season, resulting in 90 days and 15.2 matches missed by each club each season. (3,4).
There are various types of hamstring injuries, the most common ones are strains but contusions can also occur and are usually a result of contact in sports. (5,6) Muscle strains or contusions can be divided into three grades: mild, moderate and severe. Mild injuries are the result of a few torn muscle fibres, minor swelling and minimal or no loss of strength or restriction of movement. A moderate injury involves more damage and loss of strength. Severe injuries extend across the whole cross sectional area of the muscle resulting in total lack of muscle function. (1, 6)
So how can we prevent hamstring injuries? Firstly we need to understand how they happen. The hamstring is a bi-articular muscle that works by flexing the knee and extending the hip. In sports, most hamstring injuries occur whilst running, sprinting or jumping. Studies show that the majority of hamstring injuries occur in the later phase of the leg swing, as the hamstring acts to decelerate the movement of the knee extension. In this stage, the muscle is under tension whilst lengthening. The hamstring changes from an eccentric function in the late swing applied to decelerate the knee extension to a concentric function by becoming an active extensor of the knee joint. (3, 5, 7). Most injuries occur during this stage as the hamstring undergoes a rapid change from eccentric to concentric function. (8)
There are various modifiable factors that can affect the occurrence of hamstring injuries in footballers. Some of the most common factors include insufficient warm up, hamstring tightness or previous injury, muscle fatigue and / or an imbalance of muscular strength with a low hamstring to quadriceps ratio (H:Q). (9) Returning back to sport prior to full recovery can increase the risk of a recurrent or more severe injury. (7) It is unclear whether flexibility is a cause or consequence of hamstring injuries. A study by Witvrow et al (10) showed that footballers who sustained a hamstring injury had significantly less flexibility in their hamstring muscles following the injury. It also showed that they had less flexibility prior to their injury when compared to the uninjured group.
Hamstring rehab can be a lengthy process, with treatment time frames from a few weeks for minor injuries to 6 months for the return to sport post severe injuries. Various methods of treatment can be used, but the primary objective of a a rehabilitation program is to restore function of movement in the shortest possible time. Treatment is classed into different phases, which the athlete would need to undergo prior to returning to sport. The first phase of rehab is to reduce swelling and inflammation and minimise pain. During the second phase the athlete then follows a concentric strength rehabilitation program to prevent muscle atrophy and promote healing. In the third phase, eccentric movements and stretching is introduced to maintain flexibility and prevent a rehabilitation induced re-injury. Once these stages are complete, the athlete can then start the return to training process and followed by the return to sport once fully recovered. This correct timing for return to sport is important to avoid re-injury. This is normally based on normalised strength and flexibility tests and the ability to carry out sport specific movements and actions pain free. Returning to sport prior to full rehabilitation is more likely to induce re-injury. (5-7)
Hamstring injury prevention is an important part of training and preparation for most competitive sports. Studies by Woods et al. (3) show that hamstring injuries can be prevented to an extent if athletes are assigned the correct training programs. The study showed that over two seasons some football clubs sustained very few hamstring injuries whereas other clubs reported a higher rate of reoccurrence. This suggests that hamstring injuries can be prevented and managed. (3). Various factors can be modified through the injury prevention program including flexibility and strength. These are also essential for maximum performance so would be beneficial to focus on these when designing the training programs for football players.
Hamstring injuries usually occur when forces in excess of the mechanical limits of the tissue cause mechanical disruption (11-12). In order to increase the safety injury threshold, increasing the capacity of the tissue is a key injury prevention strategy. Eccentric strength training is one of the most researched and recommended evidence-based strategy for hamstring injury prevention programs. Studies are unclear whether this type of training is effective due to increased strength or due to increased length of the bicep femoris. (14) Shorter fascicles may be more susceptible to over-stretching and damage following powerful eccentric movements, such as the terminal swing phase of high speed running. (15, 16).
Various factors need to be considered when designing a strength training program. Hamstrings contribute to flexing the knee and extending the hip. Weak hip extension strength was identified as a risk factor for hamstring strength injuries in elite level sprinters. (17) When tailoring programs for individual athletes, force-velocity profiling is used to address areas of potential improvement for the individual. This will be useful for the practitioner when selecting the appropriate exercises for the athlete. If the athlete shows deficits in explosive strength, this will limit the ability to exert maximal sprint. Deficits of 30% are observed in eccentric rate of force development for athletes returning to sport following a previously injured hamstring. (18)
Eccentric training plays an important role in pre season, when coaches are designing the training plans. It is important to recognise the need for optimal hamstring function - maximal and explosive strength across the force-velocity profile. Isometric, eccentric and concentric actions are all essential in developing an effective hamstring injury prevention program. (19) A more intense approach would be to follow the full nordic hamstring exercise program. Isometric training has gained popularity over the recent years, with more practice-based research in this area.
High speed running, acceleration and peak running speed in training are highly specific and can produce positive performance benefits due to their specificity and large hip and knee joint torques. (20) These provide fewer barriers to implementation as well as bio-mechanical symmetries to the HSI mechanism. Although there is more research on the commonly assessed NHE, recent research on hamstring adaptations to sprint running shows that repeatedly achieving near peak running speeds in training is associated with lower HSI risk. (21) High speed running of speeds within 95% of maximum speed once to twice per week alongside with gym based individualised strength training programs (including both knee and hip dominant movements, and a combination of isolated and compound exercises) has shown to help with preventing hamstring injuries in football players.
The type, intensity and volume of exercises should vary depending on the individual player as well as their weekly training schedule and match times. Players who have an intense training program and regularly start or play long minutes on a weekly basis would not benefit from a program intense on eccentric loading. Other considerations are testing player’s eccentric strength and asymmetry to design tailored programs for each individual based on their physiological requirements. Fatigue resistance can be tested using the single leg bridge to capacity test to assess players prior to returning to play. (22)
Conclusion: Player and coach buy-in plays an important role as this could limit the effectiveness of the program if not implemented well by the club. It is important to educate both players and staff as to why this is important and how they will benefit from it, not only for individual players, but as a team on the whole. The injury prevention program should be tailored for the individual as different players will have different factors based on their individual risk profile. Hamstring injuries account for around 12% (A) of total injuries in elite football, so the hamstring injury prevention program should be included alongside the injury prevention program designed for the remaining 88% of injuries in general.
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