Hamstring Injuries in Sports

Hamstring Strain Injury in Athletes

• Hamstring strains occur due to sudden forceful contraction or intense stretching of the hamstring muscles. High mechanical stress leads to this
• Characterized by sharp pain in the back of the thigh, caused by hamstring muscle fiber disruption, without direct external impact.
• High-speed running, jumping, kicking, and explosive movements with rapid directional changes (lifting objects from the ground) frequently cause hamstring strains.
• A professional soccer team of 25 players can expect approximately 7 hamstring strains per season
• Hamstring strains can result in a significant loss of competition time, ranging from 3 to 28 days or more, depending on injury severity.

Relevant Anatomy and Biomechanics

• The hamstring complex, except for the biceps femoris short head, is a biarticular structure that crosses both the hip and knee joints.
• Concentric contractions in the complex cause hip extension and knee flexion, while eccentric contractions control hip flexion and knee extension.
• During many sports activities, the hamstring muscles produce high levels of force eccentrically for stabilization across the hip and knee joints.
• The inability to produce sufficient force during lengthening positions increases muscle susceptibility to injury.
• Following a hamstring injury, peak knee flexion torque shifts to a shorter musculotendon length (increased knee flexion angle), potentially increasing recurrence due to compromised force development within elongated positions.
• High-speed running is a common cause of hamstring strains due to the high activity and rapid lengthening of the hamstrings during the terminal swing phase before foot contact.
• Hamstring muscle force increases by about 1.3 times as running speed increases from 80% to 100% maximum, with the greatest stretch experienced in the long head of the biceps femoris.
• Injury location within the hamstring complex (intramuscular tendon of the biceps femoris long head versus proximal tendon of the semimembranosus) affects recovery time. Injuries to the intramuscular portion heal faster than those involving the proximal free tendon.

Risk Factors

• Non-modifiable: Previous hamstring strain is the most significant risk factor, with a 2-6 times higher recurrence rate post-injury. Age is also a factor, where athletes older than 23/25 years show a higher risk.
• Modifiable: Hamstring weakness during eccentric contraction, lumbopelvic weakness, and an imbalance between hamstring and quadriceps strength

Examination

• Sudden onset of posterior thigh pain is a characteristic symptom.
• Other symptoms may include audible popping sounds, antalgic gait (shortened stride length), bruising (ecchymosis), posterior thigh swelling, and pain with sitting or direct pressure.
• Physical examination reveals pain and weakness during resisted knee flexion/hip extension and pain during passive hip flexion/knee extension. Palpation of injury site, tenderness, mechanism of injury, and the time to return to pain-free walking.

Muscle Strength Measurements

• Hamstring strength testing is done in the prone position, with hip stabilization at 0° extension. Medical and lateral hamstring muscles can be assessed using internal/external tibial rotation at different knee flexion angles (90° and 15°).
• Hip Extension strength is evaluated with the knee at 90° and 0°, applying manual resistance to the distal posterior thigh and heel.

ROM Measurements

• Range of motion is assessed through the passive straight leg raise test and active knee extension test.
• Hamstring tightness is indicated if hip joint angle is <80° during passive straight leg raise and knee flexion angle >20° during active knee extension test.
• Acute hamstring injury (<5 days) can be assessed reliably using the active knee extension test.
• Significant increase in ROM on injured side compared to uninjured side suggests avulsion injury.

Prognostic Factors

• Injury proximity to the ischial tuberosity correlates with recovery time, with more proximal injuries needing longer rehabilitation.
• Excessive stretching injuries require longer rehab compared to high-speed running injuries.
• Injuries to the proximal free tendon of the hamstring take longer to recover than injuries to the musculotendon junction
• Athletes taking >1 day to walk pain free post- injury are more likely to need >3 weeks rehab before returning to 100% sport functions
• Active knee extension test doesn't determine return-to-sport time

Rehabilitation Goals and Intervention

• Early rehabilitation focuses on pain management, gait normalization, and gentle strengthening.
• Progressive agility and trunk stabilization exercises (PATS) enhance lumbopelvic control, reduce risk of re-injury.
• Controlled early loading through frontal plane movements, while avoiding end-range hamstring lengthening, promote PATS benefits.
• Eccentric strengthening, following acute injury, promotes better muscle function. Initiating eccentric strengthening early can reduce injury recurrence risk. Focus on concentric contractions (initially) in the mid-range, and move to end-range with increased load as strength improves.
• The final step involves sport-specific drills and return-to-sport testing, prioritizing re-injury risk mitigation.

Progressive Agility and Trunk Stabilization (PATS) Program

• A PATS program within the first week of a hamstring injury significantly reduces injury recurrence rates in the first 2 weeks and 1 year after returning to sports.
• Exercises like sidestepping, caroticas, boxer shuffle, and rotating side planks (3 sets of 20 repetitions each) are involved.

Progressive Running Program

• A three-stage protocol for a gradual return to high-speed running and sprinting and involves minimal pain, starting with slow jogging (25% of max speed), progressing to moderate-speed running (50% of max speed), and culminating in progressively increasing intensity toward maximum speed (up to 100% of max speed). Increment of 5-10% to reduce the risk of re-injury.

Eccentric Exercises

• Eccentric hamstring exercises are a common intervention to prepare athletes for high-speed running, address strength and muscle structure deficits, and prevent re-injury (research supports this over concentric training).
• Progressive exercises are done when full ROM is achieved with a pain rating ≤4/10

End Range Eccentric Strengthening Examples

• Single-limb windmill, single-limb chair bridge, single-leg deadlift, and supine bent knee walk-out.

Clinical Practice Guidelines

• Guidelines recommend using eccentric training with stretching, strengthening, stabilization and progressive running programs to improve return-to-play (RTP) time.

Interventions after Injury

• The systematic review noted that agility/stabilization exercises done after injury were associated with a lower risk of re-injury compared to only stretching/strengthening.

Injury Prevention of First-Time Injury

• Include components like warm-up exercises, stretching, stability training, strengthening and specific sport-related functional movements (Agility, high-speed running) as part of an injury prevention program.

Return to Sport

• A combination of clinical assessments, performance testing, (sprinting, agility, hopping), and isokinetic dynamometry informs RTP decision-making.

Return to Sport Criteria

• Full pain-free hip and knee range of motion;
• Maximal isometric strength;
• Negative hamstring test;
• Normal isokinetic ratio for hamstring on concentric to quadriceps eccentric;
• No pain during functional/sport-specific activities;
• No pain with active hamstring tests.
• No palpable tenderness along the posterior thigh;
• No pain or apprehension during functional/sport-specific activities.

Return to Sport Implications

• Imaging studies indicate ongoing muscle injury, even after athletes meet criteria.
• Morphologic/strength deficits may remain for athletes who followed return to sport protocols.
• Post-return progressive eccentric and lumbopelvic strengthening is vital to reach pre-injury performance levels and reduce risk of re-injury.

Summary

• Initial rehab focuses on pain, gait normalization, and mild strengthening.
• PATS, eccentric exercises enhance stability and lower re-injury risk.
• Athletes need to meet criteria like full range of motion and pass strength tests.
• Continued eccentric and core strengthening prevent future injuries.

References

• Specific research articles are cited in the provided text, however, these references are not included in this summary, as requested.