Hamstring strains are a common injury in running and pivoting sports, and managing them effectively is crucial for reducing recovery time and preventing re-injury. Here’s a detailed overview of the mechanisms, types, and grades of hamstring injuries, along with management strategies and criteria for exercise progression:
Mechanisms of Hamstring Strain Injury
Hamstring strains typically result from a combination of high muscle-tendon unit forces, extensive muscle-tendon unit lengthening beyond moderate lengths, and high-velocity movements. These factors create a high-risk environment for injury, especially in sports that require running and pivoting.
Types and Grades of Hamstring Injuries
- Types of Injuries:
- Myofascial (Type A): Heals faster.
- Musculotendinous Junction (MTJ) (Type B): Heals faster.
- Tendon (Type C): Takes longer to heal and requires more protection during early stages, with higher recurrence rates.
- Grades of Injuries:
- Grade 0:
- 0a: Focal neuromuscular injury with normal MRI.
- 0b: Generalized muscle soreness with normal MRI or characteristics of DOMS.
- Grade 1: Small muscle tears with pain during or after activity, but normal range of movement and maintained strength.
- Grade 2: Moderate muscle tears with pain that necessitates stopping activity, limited range of movement, and detectable weakness.
- Grade 3: Extensive muscle tears with sudden onset pain, reduced range of movement, and obvious weakness.
- Grade 4: Complete muscle or tendon tears with significant pain, immediate activity limitation, and a palpable gap.
- Grade 0:
Management of Hamstring Strains
When to Start Loading
After initial protection, which can last from a few days to weeks depending on the injury type and grade, the primary goal is to progressively load the recovering tissue to promote optimal adaptation back to full strength, elasticity, capability, and function. If you can walk normally and pain-free, it’s usually safe to start gradually loading the muscle.
Criteria for Exercise Progression
Exercise progressions should be based on specific adaptation goals, considering tissue healing, injury type, and symptoms such as pain. Hamstring flexibility is not a consensus criterion for progression, but loading the hamstring at longer lengths can improve flexibility. Strength, rather than pain, is the most important criterion for progression, with some level of pain (pain ≤4 on a numeric rating scale) being acceptable.
Stages of Rehabilitation
- Early Stages:
- Protect injured tissue from loading at length and elastic loads.
- Focus on isometric or shortened muscle length strength exercises.
- Avoid high force development activities; instead, work muscles through a pain-free range.
- Mid-Stages:
- Apply heavier concentric loads to encourage earlier adaptation within connective tissue.
- The application of paced eccentric loads at this stage is debated.
- Late Stages and Return to Sport:
- Integrate assessment of symptoms, strength, and response to previous loading for progression.
- Some activities (e.g., sprinting) should remain pain-free, while others can follow a pain threshold approach.
- Emphasize running, sprinting, full outer length strength, and eccentric strength as key components for returning to sport and discharge.
Reducing Re-injury Rates
Stretching is often overrated while strength is overlooked. Progressive eccentric loading, criteria-based programs, and running-specific exercises focusing on high-speed running combined with muscle lengthening (eccentric contraction) are promising strategies for reducing the risk of re-injury.
Summary
Effective management of hamstring strains involves understanding the injury mechanisms, accurately diagnosing the type and grade of the injury, and following a structured rehabilitation program that progresses based on strength and symptoms rather than time. A balanced approach that includes strength training, particularly eccentric exercises, and gradual return to sport-specific activities can help reduce recovery time and lower the risk of re-injury.