When can I Run? Understanding Hamstring Strain Mechanism, Rehabilitation & Prevention

Hamstring strains are a prevalent injury among athletes, particularly those involved in sports requiring explosive movements and high-speed running such as football, AFL, athletics and rugby codes. The grade of injury can vary depending on the type of tissue, location and severity of the injury. Time for return to performance can be anywhere from a few days to several weeks or even months. In this article, we discuss the anatomy and mechanisms of hamstring strain injury, risk factors, key rehabilitation considerations and preventative measures that can reduce future injury risk.

Anatomy and Mechanisms of Injury

The hamstrings are a biarticular muscle group, meaning they act over the hip & the knee. They function to flex the knee joint and extend the hip and have important actions during walking, running and jumping. During running, they act as antagonists to the anterior thigh muscles, functioning eccentrically to decelerate knee extension to protect the knee and enhance run gait function and efficiency. The hamstrings are made up of the:

• Semitendinosus muscle
• Semimembranosus muscle
• Biceps Femoris (Long head & short head) muscle

Hamstring muscles typically are injured during 3 main types of activities: sprinting based injuries inclusive of accelerations; high-intensity decelerations and stretch-based injuries.

1. Sprinting based injuries: typically occurring during the terminal swing phase of gait when maximal eccentric hamstring contraction occurs. The early stance phase and swing-stance transition period has also been reported as gait cycles whereby injury may occur, with different loading mechanisms contributing to injury.
2. High intensity decelerations: an often overlooked mechanism whereby braking strategies where knee is extending and the trunk is flexed, causing increased eccentric ‘stretch’ hamstring forces.
3. Stretch based injuries: typically occur when excessive, sudden stretch occurs, involving extensive hip flexion and simultaneous knee extension. Typically seen with kicking related injuries in sports such as football and AFL.

Risk Factors

Several intrinsic and extrinsic factors contribute to an increased risk of hamstring strains:

• Age
• Sex
• Body composition
• Hamstring previous injury
• Joint kinematics and mechanics
• Eccentric strength
• Fascicle length
• Muscle endurance & fatigue resistance
• Contextual factors: game situation, risk perception
• Acute & chronic loading

Although we can't influence factors such as age, sex and previous injury history, other modifiable factors including eccentric strength & fascicle length can be altered to enhance performance and reduce injury risk.

Key Rehabilitation Considerations

When reconditioning following hamstring injury, or any musculoskeletal injury for that matter, we must ask 3 key questions:

1. What are the tissue-specific considerations to return to performance?
2. What are the sport-specific considerations to return to performance?
3. And how do we combine these two, along with the global, holistic factors of the individual required for elite performance?

Lets consider the tissue-specific considerations for return to performance following a grade 2b biceps femoris long head muscle strain for instance. Evidence highlights that:

• Biceps femoris action is hip dominant so focussing hip dominant exercises such as Romanian deadlifts, GHD hip extensions & conic pulley variations provide specificity. This differs to medial hamstring muscles (semimembranosus and semitendinosus) where they are knee dominant in nature.
• Biceps femoris long head demands are greatest during the leg deceleration and foot strike activities when eccentric-concentric muscle transition occurs, requiring significant eccentric strength.
• It also experiences the greatest eccentric lengthening during this phase (110% of standing length), highlighting the importance of increasing fascicle length. This influences exercises selection and programming.

Other factors that are also important to address during the rehabilitation process include:

• Lumbopelvic control
• Running mechanics
• Synergist and antagonist musculature
• Tendon stiffness

We then need to consider what activity/sport is this individual returning to? No two hamstring injuries are the same. An individual who damages there hamstring whilst kicking during AFL (stretch mechanism) has different return to performance requirements to an individual who competes track sprinting. This is important, especially during latter phases of reconditioning whereby specificity is crucial to allow return to elite performance. By having an understanding of the outcome we are aiming towards (need analysis) and what elite performance looks like for an individual, we can then ‘work backwards’ to design an appropriate, specific and progressive rehabilitation plan.

A final important note regarding the rehabilitation process, is that it is crucial to ensure appropriate, key objective measures are achieved prior to progression. “When can I run?” & “When can I return to my sport” are questions I always get asked during the rehabilitation process. Historically, time-based criteria was used during musculoskeletal rehabilitation (i.e., once you hit for example 6 weeks post injury, you were ready to return to sport). This model however, is outdated. Although timeframes provide us with a good indication of how long rehabilitation will take (and are important to respect especially for tendon-based & surgical injuries), objective-based criteria should be used. This involves setting appropriate objective markers for each stage of rehabilitation which provides us with the evidence that your hamstring is ready to progress to the next stage. Such objective criteria for hamstring rehabilitation includes: symptoms, clinical assessment tests, gym-based physical tests and pitch/grass based tests, along with consideration for acute chronic loading and mechanism specific criteria (e.g. can I sprint maximally & repeatedly). Psychosocial factors are also important to use as part of the decision making process for return to performance.

Injury Prevention

The greatest risk factor for future hamstring injuries is previous hamstrings injuries, highlighting the importance of injury prevention for this type of injury. Key factors that are important to consider when preventing hamstring injury include:

• Adequate warm up/cool down routine
• Hamstring strengthening program to address weakness and modifiable risk factors
• Monitoring of training and game loads and minimising ‘spikes’ in loading
• Ensuring adequate exposure to mechanisms - sprinting, acceleration/decelerations and kicking. This serves to act as a ‘vaccine’ to reduce injury risk
• Addressing kinematic and biomechanical factors that may overload the hamstrings. For instance, are the lumbopelvic factors (anterior pelvic tilt) that are increasing the load to the proximal hamstrings unfavourably?
• Develop fatigue resistance and monitoring hamstring fatigue

Such factors can assist in reducing the risk of hamstring muscle strain and ensure you stay fit and able to perform your sport/activity.

Closing Thoughts

Hamstring strains are a common injury in explosive sports, and recovery time can vary. The hamstrings are a biarticular muscle group that function to flex the knee joint and extend the hip. Risk factors for hamstring strains include age, gender, previous injury, and joint mechanics. Rehabilitation should focus on tissue-specific and sport-specific considerations, with objective-based criteria for progression. Injury prevention strategies include adequate warm-up, strengthening, monitoring of training loads, and addressing biomechanical factors. An experienced physiotherapist can help guide you through your rehabilitation process to ensure you return to sport ready to perform optimally.

Are you experiencing hamstring strain and not sure whether you should be running or not? Book an appointment with our friendly physiotherapists at our Brisbane CBD clinic today!

By Stephen Valassakis BSc (Hons), MSc, APA