Hamstring strains are a common injury in various sports and often require athletes to take a break from training to recover. Athletes involved in sports that involve fast sprinting and kicking are particularly at risk due to the intense demands on the hamstring muscles. About one in three athletes who experience a hamstring strain are likely to have a re-injury. This high re-injury rate is believed to be due to inadequate rehabilitation, returning to play too soon, or a combination of both. Re-injury is a major issue as it leads to more time spent out of play and further frustration for the athlete. In the following text, we will examine the current research on rehabilitating hamstring strains and determine the appropriate time for athletes to return to sports after an injury.
What are hamstrings?
Let’s start by examining the hamstrings, which are the muscles that run down the back of your thigh. The hamstrings consist of three actual muscles: the biceps femoris with a long head and a short head, semimembranosus, and semitendinosus. These muscles work on two different joints, the hip and the knee. Specifically, they extend the hip and flex the knee, making them vital for sprinting as they control the movement of the lower leg throughout the stride cycle and aid the gluteal muscles in generating powerful hip extension. Additionally, the hamstrings have other functions such as acting as a secondary knee stabilizer and helping control leg rotation. Some evidence suggests that they also serve as shock absorbers during foot contact in sprinting.
The hamstrings, like other muscles, have the ability to perform both eccentric and concentric movements. In concentric muscle action, the muscle contracts and shortens, while in eccentric action, the muscle elongates while experiencing increased tension. Eccentric actions involve greater force and speed than concentric actions, making them more prone to causing injuries.
In the sprint cycle, as the thigh reaches its maximum flexion angle in front of the body, the lower leg starts to move forward. This is important as it allows the athlete to cover more distance per stride and increase their stride length. However, the hamstrings are actively involved in controlling this movement while the lower leg is moving forward. The hamstrings first slow down the lower leg by lengthening eccentrically. Once the lower leg stops moving forward, it quickly accelerates towards the ground, mainly through hip extension that requires the hamstrings to contract concentrically. The more powerful this movement, the shorter the time the foot spends on the ground, which helps enhance stride frequency. After the foot makes contact with the floor, the hamstrings continue to work along with the gluteal muscles to actively propel the body over the foot. These actions highlight the significant role played by the hamstring muscles in the sprint cycle.
Why do we injure our hamstrings?
Taking into account what I have previously mentioned, we can delve into the reasons behind hamstring injuries. Initially, the muscles have a dual function, acting upon two separate joints. This leads to an increased range of motion for the muscles, thus raising the probability of injury. Moreover, they undergo an eccentric action during sprinting, which involves applying a substantial amount of force. Muscles experience tearing when they are unable to withstand the force exerted upon them. If there is an underlying problem with the hamstring, it is more susceptible to getting injured at this stage – as indicated by research studies. According to Petersen & Holmich (2005) in a review article, most hamstring injuries occur either during the eccentric contraction (particularly in the later phase) or just prior to foot contact. Malliaropoulas et al. (2012) further note that the hamstrings undergo the greatest musclo-tendonous stretch right before ground contact, which is identified as the most probable point of injury.
Risk factors associated with a hamstring injury
Some of the risk factors linked to a hamstring injury encompass a wide range of factors.
- Imbalance of Muscular Strength – Orchard et al. (1997) found that if the quadriceps were much stronger than the hamstrings, this increased the risk of a hamstring injury. They found that a ratio of below 0.6 for hamstring:quadracep strength increased the risk of injury. This ratio was mirrored in the Yeung et al. (2009) study on sprinters; the researchers found that if the ratio was below 0.6, then hamstring injury was seventeen times more likely to occur.
- Muscle Fatigue – Woods et al. (2004) found that significantly more hamstring injuries occur towards the end of a game, indicating that muscle fatigue plays a role in hamstring injury. Pinniger at al. (2000) demonstrated that repeated sprint bouts reduced hamstring function, meaning that the fatigued hamstring muscles could absorb less energy before reaching the level of stretch that caused injury.
- Hamstring tightness – Harting et al. (1996) found that hamstring flexibility reduced the risk of injury in a group of military recruits. This finding is a little controversial, as there are also a some studies that illustrate that lack of hamstring flexibility does not increase the risk of injury.
- Insufficient warm-up
- Previous Injury – Previous injury both within the hamstring muscles and surrounding muscles and structures increases the chance of injury. Koulouris et al. (2007) found that following anterior cruciate ligament (ACL) reconstruction surgery, the risk of a hamstring injury was significantly elevated. This is because the hamstrings play a role in stabilising the knee alongside the ACL – and if the ACL cannot perform this function, the hamstrings are placed under additional strain and load.
- Insufficient Recovery Period – Return from the previous injury before complete recovery
- Inadequate strength in hamstrings – Yeung et al. (2009) found that hamstring injuries were more likely to occur early in the season, when hamstring conditioning was not as high. In their study, 60% of hamstring injuries occurred within the first 100 hours of a training program.
Rehabilitation and Strengthening Phases
Rehabilitation following a hamstring strain is commonly separated into three distinct phases. The initial phase, which usually spans a few days, concentrates on safeguarding the injured hamstring muscle. During this period, athletes typically engage in gentle range of motion and coordination exercises, while refraining from isolated hamstring strengthening and excessive stretching. The second phase varies in duration and prioritizes gradual strength development and the improvement of coordination in the trunk and legs. Athletes generally begin a progressive strengthening and running regimen at this stage, while avoiding intense running and maximum hamstring strengthening. The last phase aims at returning to sports-specific activities. During this time, athletes typically partake in intense hamstring strengthening, high-intensity running, and agility training.
Receiving professional guidance from a physical therapist during the rehabilitation process is crucial for ensuring optimal recovery after a hamstring strain. For instance, your therapist can include exercises that specifically target your injured hamstring muscle in order to prevent your other hamstring muscles from compensating for the injury. They can also carefully monitor your symptoms to determine the appropriate level of exercise progression for your injured hamstring. While you may have some concerns about experiencing pain during your exercises, research indicates that it is not necessary to completely avoid activities that provoke pain during rehabilitation. In fact, a recent study discovered that individuals who performed exercises with pain levels of up to 4/10 displayed improved hamstring strength compared to those who only did pain-free exercises. Overall, physical therapists are well-equipped to guide you through the various stages of rehabilitation and choose exercises that are suitable for your specific needs and recovery.
Returning to Playing Sports After a Hamstring Injury
Having covered the rehabilitation process, the next crucial question is determining when it is safe to resume playing your sport. This question can be challenging to answer due to a lack of agreement in the literature regarding the most suitable timing for return to play. However, research has shed light on factors that contribute to longer recovery times and has provided information on test batteries that can be employed to prevent premature return to sport. Some factors associated with extended recovery after a hamstring strain include experiencing intense pain at the time of injury, hearing a popping sound, bruising on the back of the thigh, and muscle pain during daily activities. Thus, if you encounter one or more of these issues, your recovery process might take longer. Recent studies also recommend a progressive testing battery that includes evaluations of isolated and functional hamstring strength, high-speed hamstring stretch tests, and assessments of sports-specific movements to determine your readiness to return to your sport.
Nevertheless, there is an additional aspect that has received attention in recent research regarding return to sport, which is the biological healing time of hamstring muscle injuries. This factor is often overlooked when determining the appropriate time for athletes to resume their sporting activities. This is evident from the fact that most athletes are cleared for return within 2-3 weeks, while biological healing of the injury site can take up to 4 weeks. It is crucial to note that complete biological healing is not a prerequisite for returning to sport, as it can continue for several months after the injury. However, it is important to allow the hamstring to heal sufficiently to withstand the demands of sporting activities. While healing times may vary for each individual, the study authors recommended a minimum waiting period of 4 weeks before athletes should consider returning to their respective sports.
When deciding on when to return to sport after a hamstring strain, several factors should be taken into account. However, initiating a rehabilitation program under the guidance of a physical therapist is a commendable initial action. Subsequently, the therapist can assist in determining the most suitable time for resuming sports activities by considering the time required for biological healing as well as conducting return to sport test batteries. This process should provide assurance that you are making the most well-informed decision regarding the appropriate timing for returning to your sport following the injury.
