Hamstring injuries are the most common muscle injuries in sport. In football alone, they account for approximately 12 to 17 percent of all injuries and produce more missed training days than any other single injury type. In sprinting, they are the primary injury concern from junior through to elite level. And despite decades of research and evolving rehabilitation approaches, recurrence rates remain stubbornly high: between 14 and 34 percent of athletes who sustain a hamstring strain will sustain another within the following season.
Understanding why hamstring injuries are so common and so prone to recurrence is the foundation of effective prevention. This guide covers the risk factors, the evidence behind the most effective preventive interventions, and a practical programme that can be implemented immediately.
Why Hamstrings Are Vulnerable
The hamstrings are injured almost exclusively during one specific mechanical scenario: the late swing phase of sprinting, when the hamstrings are simultaneously at their longest length (the hip is flexed and the knee is extended) and producing their highest forces (decelerating the forward-swinging leg). This combination of high force and long muscle length creates the perfect conditions for muscle fibre damage.
The specific moment of injury:
During the late swing phase of maximum-speed sprinting, the hamstrings must produce eccentric forces of approximately 8 to 10 times body weight in some sprint athletes. These forces are produced when the hamstrings are near their maximum length, in the position where they are most vulnerable to structural damage.
This is why hamstring injuries in sport are overwhelmingly sprinting-related rather than occurring during slower running, and why the most effective prevention exercises specifically target the hamstrings at long muscle lengths under high eccentric loads.
Risk Factors for Hamstring Injury
Understanding the risk factors allows prevention efforts to be targeted at the specific deficits most relevant to an individual athlete.
Previous Hamstring Injury
The single strongest predictor of hamstring injury is a previous hamstring injury. Athletes with a history of hamstring strain have approximately two to six times the risk of sustaining another compared to athletes without a prior injury. This elevated risk persists for at least two seasons following the initial injury.
Why previous injury increases risk:
After a hamstring strain, the muscle heals with scar tissue that has different mechanical properties from the original muscle. The scar tissue is less extensible and less capable of handling high eccentric loads, creating a zone of weakness within the muscle belly. If rehabilitation is incomplete and the full strength and flexibility of the hamstring is not restored before return to sport, this weakness remains.
Eccentric Hamstring Weakness
Insufficient eccentric hamstring strength is the most consistently modifiable risk factor identified in research. Athletes with lower eccentric hamstring strength (as measured by the Nordic curl or isokinetic dynamometry) have significantly higher rates of hamstring injury than those with greater eccentric strength.
Why eccentric strength specifically:
As described above, hamstring injuries occur during the eccentric phase of the late swing (the hamstrings are lengthening under load). Concentric hamstring strength (the ability to flex the knee against resistance) is less directly relevant to the injury mechanism than the ability to control high forces while lengthening.
Hamstring-to-Quadriceps Strength Ratio
The conventional (concentric) hamstring-to-quadriceps strength ratio and the functional ratio (eccentric hamstrings to concentric quads) are both associated with injury risk when significantly imbalanced. A ratio below approximately 0.6 (hamstrings producing less than 60 percent of the quadriceps force) is associated with elevated risk.
The practical implication:
Athletes in quad-dominant training programmes (heavy squatting without equivalent posterior chain work) may develop a strength imbalance that increases hamstring injury risk. Balancing posterior chain and anterior chain loading is a primary prevention strategy.
Side-to-Side Asymmetry
Significant side-to-side hamstring strength asymmetry (greater than 10 to 15 percent difference between legs) is associated with elevated injury risk, particularly for the weaker side. As covered in the single leg hamstring bridge article on this site, the single-leg hamstring exercises are the primary tool for identifying and addressing this asymmetry.
Training Load Error
Rapid increases in sprint training volume or intensity without adequate preparation are a primary cause of hamstring injury in team sport athletes. Hamstring injuries in training (as opposed to match play) most commonly occur in the first few weeks of pre-season or after a return from injury or illness, when training loads increase rapidly after a period of reduced loading.
Fatigue
Hamstring injuries are disproportionately common in the late stages of training sessions and matches, when muscular fatigue reduces the hamstrings’ ability to produce the eccentric forces needed during sprinting. A 2018 study found that approximately 25 percent of hamstring injuries in professional football occurred in the final 15 minutes of each half, consistent with fatigue as a contributing factor.
Age
The risk of hamstring injury increases with age in sport, with athletes over 25 having approximately twice the risk of those under 20. The specific mechanisms are not fully understood but likely involve reduced muscle compliance with age, longer recovery times between training sessions, and accumulated load on previously strained tissue.
Poor Sprint Mechanics
Running mechanics that increase the hamstring load during the late swing phase (excessive anterior pelvic tilt, insufficient hip extension, overstriding) may elevate hamstring injury risk. Gait retraining to address these mechanics is a component of comprehensive hamstring injury prevention programmes in some elite sporting settings.
The Evidence on Hamstring Injury Prevention
The Nordic Hamstring Curl: The Most Evidence-Supported Intervention
The Nordic hamstring curl is the single most evidence-based hamstring injury prevention exercise. As covered in the how to do nordic curls at home article on this site, the Nordic curl involves kneeling with the ankles fixed, lowering the body toward the floor by allowing the knees to extend, and controlling the descent eccentrically with the hamstrings.
The evidence:
Multiple large randomised controlled trials and systematic reviews have examined the effect of Nordic hamstring curl programmes on hamstring injury rates in team sport athletes. The consistent finding across these studies is a 50 to 70 percent reduction in new hamstring injuries and a 70 to 85 percent reduction in recurrent hamstring injuries in athletes who perform the Nordic curl programme versus those who do not.
This is among the strongest evidence for any injury prevention exercise in sports medicine. The effect size of the Nordic curl on hamstring injury rates is comparable to or greater than the effect of ACL prevention programmes on ACL injury rates.
Why it works:
The Nordic curl specifically develops the eccentric hamstring strength at long muscle lengths that is most directly relevant to the late-swing phase injury mechanism. Research has found that regular Nordic curl training significantly increases the angle of peak torque during isokinetic hamstring testing (shifting peak force production to longer muscle lengths) and increases fascicle length in the biceps femoris (the primary site of hamstring strains). These structural and mechanical adaptations directly address the tissue-level vulnerability that makes the hamstrings susceptible to strain.
The adoption problem:
Despite the strength of the evidence, the Nordic curl is significantly underutilised in sport. A 2019 survey of professional football coaches found that fewer than 5 percent used the Nordic curl consistently with their squads, often citing perceived difficulty, player discomfort, and concerns about hamstring soreness as barriers. These barriers are manageable with a progressive introduction as described in the nordic curl progression article on this site.
Hip Extension Strengthening
Exercises that develop the hamstrings through the hip extension function (Romanian deadlift, single-leg RDL, hip thrust, good morning) address the hamstrings’ role in hip extension during the push-off phase of sprinting and complement the Nordic curl’s eccentric knee flexion emphasis.
The evidence:
While the evidence base for hip extension exercises in isolation is less extensive than for the Nordic curl, research on comprehensive hamstring injury prevention programmes (which typically combine eccentric knee flexion and hip extension work) shows greater injury reduction than Nordic curl-only programmes. A 2023 systematic review suggested that programmes combining Nordic curls with hip extension strengthening produced the most consistent injury prevention outcomes.
Progressive Sprint Training
Because hamstring injuries are most common during sprinting, progressive exposure to high-intensity sprinting (rather than sudden introduction of maximal sprint efforts) is a primary prevention strategy in team sport.
The evidence:
Research on GPS-monitored sprint training in professional football has found that athletes who perform more high-speed running volume in the weeks preceding injury-prone periods (pre-season, post-injury return) have lower hamstring injury rates than those who perform less. This finding supports the concept of building sprint tissue tolerance through progressive exposure before high-load periods.
The practical approach:
Gradual return to maximum-speed sprinting after pre-season, after injury, or after illness. Sprint training sessions building progressively from 70 to 80 percent of maximum effort before full-speed sprinting is introduced.
Warm-Up Protocols
Structured dynamic warm-up protocols that include sprint-specific preparation (dynamic hamstring stretching, high-knee drills, progressive acceleration runs) before sprint training sessions reduce hamstring injury risk by ensuring the hamstrings are adequately prepared for the demands of high-speed running.
A Practical Hamstring Injury Prevention Programme
The following programme is based on the evidence reviewed above and is appropriate for team sport athletes, runners, and anyone with a history of hamstring injury or elevated injury risk.
Phase 1: Foundation (Weeks 1 to 3)
Goal: Establish hamstring activation and basic eccentric loading tolerance before introducing the Nordic curl.
3 times per week:
- Nordic curl introduction (hands-catch version): 2 sets of 5 (as covered in the how to do nordic curls at home article on this site)
- Stability ball hamstring curl: 3 x 10
- Single-leg hamstring bridge: 3 x 10 per side (as covered in the single leg hamstring bridge article on this site)
- Romanian deadlift (light load): 3 x 10
Sprint preparation:
- Sprint efforts limited to 70 to 80 percent maximum effort
- Progressive sprint volume increase of no more than 10 percent per week
Phase 2: Loading (Weeks 4 to 8)
Goal: Develop progressive eccentric hamstring strength and address asymmetries.
3 times per week:
- Nordic hamstring curl: 3 x 6 to 8 (as covered in the nordic curl progression article on this site)
- Single-leg RDL: 3 x 8 per leg (as covered in the single-leg romanian deadlift article on this site)
- Stability ball hamstring curl (slow eccentric): 3 x 8
- Hamstring curl with band: 3 x 12 per side (as covered in the hamstring curl with resistance band article on this site)
- Side-to-side asymmetry check: perform all single-leg exercises and address any side greater than 10 percent weaker with an additional set
Sprint preparation:
- Progress to 85 to 90 percent effort sprinting
- Include 2 to 3 maximal effort acceleration sprints (20 to 30 metres) per session
Phase 3: Maintenance (Week 9 onwards)
Goal: Maintain the eccentric hamstring strength and sprint conditioning developed in Phases 1 and 2 throughout the season.
2 times per week:
- Nordic hamstring curl: 2 x 8 to 10
- Single-leg RDL: 2 x 8 per leg
- Single-leg hamstring bridge with slow eccentric: 2 x 8 per side
Sprint preparation:
- Full-speed sprint training integrated into training sessions
- Continue progressive sprint volume management throughout the season
Pre-Training Warm-Up (Every Session)
Before every sprint training session or team sport practice:
- Dynamic hamstring stretching: 10 leg swings per leg
- High-knee march: 20 metres
- High-knee skip: 20 metres
- Progressive acceleration runs: 3 x 40 metres at 70, 80, 90 percent effort
Special Considerations
Returning After Hamstring Injury
Return to sprinting after hamstring injury should be guided by clinical criteria rather than a fixed timeline. Key criteria before return to full-speed sprinting:
- Pain-free walking, jogging, and progressive running at up to 80 percent effort
- Hamstring strength within 10 percent of the uninjured side (assessed by single-leg hamstring bridge, Nordic curl, or isokinetic testing)
- Pain-free performance of the specific sprint mechanics relevant to the sport
- Ability to perform reactive and unexpected direction changes without pain or apprehension
As covered in the what causes a knee to buckle and buckling knee exercises articles on this site, any associated knee instability must also be resolved before return to full sprint training.
Managing High-Risk Periods
The highest-risk periods for hamstring injury are:
- The first 3 to 4 weeks of pre-season (after a period of reduced sprint training)
- The first week of return after illness or a period of rest
- Congested fixture periods where fatigue accumulates
During these periods, maintain the Nordic curl and hip extension work even when overall training volume is high. The preventive exercises should be among the last to be removed from the programme when time is limited.
Frequently Asked Questions
How long do I need to do Nordic curls to prevent hamstring injuries?
The evidence from long-term follow-up studies shows that the injury-preventive effect of the Nordic curl is greatest when training is maintained consistently over a full season. Studies that have followed athletes over multiple seasons find that injury rates begin to rise when Nordic curl training is discontinued. The Nordic curl should be viewed as a year-round training component rather than a pre-season intervention, with maintenance volumes of 2 sets of 8 per week being sufficient once the initial loading phase is complete.
Are hamstring stretches effective for preventing hamstring injuries?
Static hamstring stretching alone has not been shown to significantly reduce hamstring injury rates in prospective research. Flexibility is one factor in hamstring health but is not the primary modifiable risk factor. Eccentric strength (developed through the Nordic curl and slow eccentric exercises) has a significantly stronger evidence base for injury prevention than flexibility alone. This does not mean stretching is harmful: maintaining reasonable hamstring flexibility is appropriate, but it should not be the primary prevention strategy.
My hamstrings are always tight. Does that mean they are at high injury risk?
Not necessarily. Hamstring tightness and hamstring weakness are two different issues that frequently coexist but do not always. As covered in the back of thigh pain article on this site, perceived hamstring tightness is often related to neural sensitivity rather than true muscle shortness, and may reflect the nervous system’s protective response to an area that it perceives as vulnerable. Developing eccentric hamstring strength (which addresses the actual injury mechanism) is typically more effective than stretching alone for people with chronically perceived tight hamstrings.
Can recreational runners use this programme?
Yes. The programme is appropriate for recreational runners, particularly those with a history of hamstring strain or those who are increasing their running volume. The Nordic curl programme has been studied in recreational running populations with similar injury-preventive effects to those seen in team sport athletes. The sprint preparation component should be modified to reflect the runner’s training structure (progressive increase in running pace rather than team sport sprint drills).