Background
Hamstring injuries are one of the most common injuries in athletics accounting for up to 20% of all sports injuries (Wing et al. 2020). Injuries can be both acute due to a traumatic injury or overuse in nature due to exposure to higher training volumes over time. Both types of injuries can lead to a significant loss of practice and competition time in athletes. In the acute category injuries are graded on a 3 point scale of severity based on the degree of tissue damage in the muscle. Depending on the severity of the injury, hamstring injuries can range from 1-2 up to 12 weeks of time off training. Importantly, athletes with a previous history of hamstring injury have been found to be 3-4 times more likely to reinjure their hamstring in the future (Lee et al. 2018).
The hamstrings can commonly become injured during running sports due to the high demand of muscle activity required, as well as, the muscle’s anatomical location spanning two joints. For example, runners often describe a moment of overload or injury when the muscle transitions from a position of stretch as it swings forward into a muscle contraction when the foot hits the ground. This muscle group can also be overstretched during a kicking motion or bending forward to pick something off the ground. During both injury mechanisms, athletes can experience a sudden, sharp pain in the posterior thigh often with a pulling or popping sensation.
Hamstring overuse and acute injuries are common among runners at all levels, particularly those who engage in sprinting. There are two main mechanisms of injury for this athlete population. First, during the late swing phase of running, the hamstring eccentrically lengthens to slow the lower leg’s advancement rate in preparation for the stance phase. The other theory suggests that during the initial stance phase, opposing forces act on the body, placing strain on the hamstring muscle. Both mechanisms underscore the importance of eccentric hamstring strengthening. In our Boulder Physical Therapy practice we often see hamstring injuries in runners with weakened hip extensors (Gluteus Maximus). This muscle imbalance leads to an overload of the hamstrings due to the lack of contribution from the gluteus maximus during the running gait.
Risk Factors
Previous researchers have found a significant number of modifiable and non modifiable risk factors for a future hamstring injury (Wing et al. 2020). Athletes often experience hamstring injuries when fatigued at the end of a practice or competitive bout of exercise. Authors have noted athletes with a relatively short hamstring were 4 times more likely to injury their hamstring compared to their peers with greater flexibility, but this remains a less consistent risk factor for injury. In addition to muscle length or flexibility, muscle strength and side to side symmetry have also been shown to influence a future hamstring injury. In our Boulder Physical Therapy and Lafayette Physical Therapy practices, an athlete with a significant loss of absolute strength or speed of muscle contraction (rate of force development) on their involved side will be a higher risk of re injury upon return to sport. As mentioned above the greatest risk of a future injury remains a previous hamstring injury. Highlighting the importance of a proper Physical Therapy rehabilitation program after initial injury. Finally, all athletes are encouraged to perform a proper warm up including dynamic lower body stretching prior to beginning their training.
Prevention
Numerous studies have investigated the effect of eccentric hamstring strengthening on reducing the likelihood of hamstring injury. One study demonstrated a 51% reduction in hamstring strains in soccer teams that included Nordic hamstring curls in their conditioning program. This proposed mechanism involves increasing muscle fascial length and improving eccentric muscle contraction control, allowing the muscle to effectively control lower leg advancement. Other exercises like the Romanian Deadlift, stiff-legged deadlift, and kickstand deadlift achieve similar eccentric loading, although they haven’t been studied as extensively as the Nordic curl. Injury prevention exercise programs should include a dynamic warm up, dynamic muscle stretching, sport specific movements, and lower body strengthening. Athletes should aim to perform these exercises 3-4 sets of 6-12 reps, 2-3 days/week.
Treatment
Hamstring injuries of all grades of severity or mechanisms of injury should be evaluated by a board certified Physical Therapist. Accurately determining the type and severity of injury allows for the most effective and efficient treatment plan. When rehabilitating a hamstring strain, it’s important to determine the stage of healing in order to progress exercises accordingly, as well as, address any underlying musculoskeletal impairments that might contribute to hamstring strain development such as gluteus maximus weakness.
In our Boulder Physical Therapy and Lafayette Physical Therapy practices, we treat injured athletes with a combined approach of manual therapy including spinal and extremity manipulation, dry needling, and high level strengthening exercises. Injured tissues require adequate loading, not rest, to remodel and heal properly. Muscles that are not rehabilitated properly remain overly sensitive during activity and the lack the force and length required to return to practice and competition without pain. In addition, it is critical to assess the entire athlete to identify causes of the initial hamstring injury including lost mobility, core weakness, running biomechanics, and muscle imbalances.
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