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Hüseyin Akbulut, MSc (2026). Hamstring Injuries: Why They Keep Coming Back. Sporeus. Retrieved, October 17, 2026. https://sporeus.com/en/sport/hamstring-injury-prevention/
Hamstring Injuries: Why They Keep Coming Back
Hamstring strains are the most common muscle injury in field sports — accounting for up to 37% of all muscle injuries in professional football — and they carry one of the highest recurrence rates in sport medicine, with estimates ranging from 14% to 34% within the same season. The persistent recurrence problem is not a mystery; it reflects both incomplete rehabilitation and fundamental misunderstandings about hamstring function that shape training practices. Understanding the anatomy, biomechanics, and evidence-based prevention strategies changes how practitioners approach this stubborn injury.
Table of Contents
Anatomy and Injury Mechanisms
The hamstring muscle group comprises three muscles: biceps femoris (long and short head), semitendinosus, and semimembranosus. They cross both the hip and knee, functioning to extend the hip and flex the knee, and — critically — to decelerate knee extension during the terminal swing phase of running.
The vast majority of hamstring strains (approximately 85%) occur at the biceps femoris long head, typically at the myotendinous junction — the interface between muscle fiber and tendon, the weakest point during forceful eccentric loading. The injury mechanism is almost always eccentric: the muscle is contracting while being forcibly lengthened.
Two primary injury mechanisms have been identified:
- Terminal swing mechanism (sprinting): During high-speed running, the hamstrings must decelerate the rapidly extending knee in late swing phase while simultaneously beginning hip extension. Peak hamstring strain occurs at approximately 30° of hip flexion with the knee nearly extended — a position that places enormous eccentric demand on the biceps femoris. This mechanism dominates in sprint sports (football, rugby, track).
- Stretching mechanism: During movements that simultaneously flex the hip and extend the knee — a high kick, splits, or extreme reach — the hamstrings are stretched to near-maximal length. Injuries at the proximal musculotendinous junction are more common in this mechanism and have a characteristically long recovery time.
Why Hamstrings Keep Coming Back
The recurrence problem has multiple contributing factors, several of which are modifiable through appropriate rehabilitation:
Scar tissue weakness: Muscle fiber repair involves the formation of scar tissue at the injury site. Scar tissue is mechanically inferior to native muscle fiber — less elastic, less forcefully contractile, and more susceptible to re-injury under the same loading conditions that caused the original strain. Rehabilitation that does not adequately load the healed tissue leaves it functionally weaker than the surrounding muscle.
Persistent eccentric strength deficits: Research consistently demonstrates that athletes return to sport with residual eccentric hamstring strength deficits at the injury site. Concentric strength may recover fully while eccentric capacity remains impaired — a dangerous combination during sprinting, where eccentric load is the primary stress. Standard return-to-sport criteria that do not include isokinetic eccentric strength assessment systematically miss this deficit.
Architectural changes: Ultrasound studies reveal that healed hamstrings show altered muscle architecture — reduced fascicle length and altered pennation angle — compared to the contralateral limb. Shorter fascicles produce force over a narrower range of motion, shifting peak force development to a shorter muscle length and increasing vulnerability at long lengths during sprinting.
Premature return to sport: Time-based return-to-sport criteria (e.g., “return after 3 weeks”) are poorly correlated with tissue readiness. Athletes who return to full sprint training before scar tissue has adequately remodeled and strength deficits have resolved face substantially elevated re-injury risk in the first 2–3 weeks back in competition.
The Nordic Hamstring Curl: Prevention Evidence
The Nordic hamstring curl (NHC) is the most studied injury prevention exercise in sports medicine. The exercise involves kneeling with the feet anchored while the athlete falls forward in a controlled eccentric contraction before lowering to the ground. It produces the highest hamstring muscle activation of any commonly used exercise and specifically loads the biceps femoris long head at long muscle lengths — precisely the position where sprint-related injuries occur.
| Study / Meta-analysis | Injury Reduction | Population |
|---|---|---|
| Petersen et al. (2011) | 70% reduction in overall hamstring injuries | Danish football players |
| van Dyk et al. meta-analysis (2019) | 51% reduction in all hamstring injuries | Multiple sports, meta-analytic |
| Al Attar et al. (2017) | 50% reduction in hamstring strain | Recreational and competitive football |
| Recurrence reduction | 85% reduction in recurrent strains | Multiple studies, football |
Despite this evidence, adoption of the NHC in professional football clubs has been inconsistent. A large survey found that only a minority of clubs performed it routinely, often citing athlete discomfort (it is notoriously challenging) and player/coach resistance. The irony is that the discomfort reflects the eccentric overload that makes it effective.
The standard progressive NHC protocol begins with 2 sets of 5 repetitions in week 1, progressing over 10 weeks to 3 sets of 12 repetitions. Off-season implementation with maintenance through the competitive season (1 session per week) preserves the injury reduction benefits.
Complete Rehabilitation Principles
Effective hamstring rehabilitation addresses the full spectrum of deficits rather than simply waiting for pain to resolve:
- Early loading (not rest): Controlled eccentric loading initiated within the first 2–3 days of injury accelerates recovery without increasing re-injury risk, according to randomized trials. Prolonged rest delays fascicle length recovery.
- Fascicle length restoration: Exercises that load the hamstring at long muscle lengths — Romanian deadlifts, Nordic curls, hip-dominant movements — are specifically targeted at restoring fascicle architecture.
- Criteria-based, not time-based return: Return-to-sprint criteria should include: no pain on palpation, normalized isokinetic eccentric strength (limb symmetry index ≥90%), passing a graduated sprint test without pain, and psychological readiness.
- Graduated sprint reintroduction: A structured return-to-sprint program progressing from 70% maximum speed through to full acceleration and high-speed running over 10–14 days is essential. Returning directly from sub-maximal running to full training exposes athletes to the re-injury spike seen in the first weeks back.
The tools to reduce hamstring injury incidence and recurrence substantially are available and evidence-based. The gap between what sport science shows and what happens in practice remains one of the most frustrating disconnects in applied sport medicine.
References
- Petersen J, Thorborg K, Nielsen MB, Budtz-Jørgensen E, Hölmich P. (2011). Preventive effect of eccentric training on acute hamstring injuries in men’s soccer: a cluster-randomized controlled trial. The American Journal of Sports Medicine, 39(11): 2296–2303. doi:10.1177/0363546511419277
- van Dyk N, Behan FP, Whiteley R. (2019). Including the Nordic hamstring exercise in injury prevention programmes halves the rate of hamstring injuries: a systematic review and meta-analysis of 8459 athletes. British Journal of Sports Medicine, 53(21): 1362–1370. doi:10.1136/bjsports-2018-100045
- Al Attar WSA, Soomro N, Sinclair PJ, Pappas E, Sanders RH. (2017). Effect of injury prevention programs that include the Nordic hamstring exercise on hamstring injury rates in soccer players: a systematic review and meta-analysis. Sports Medicine, 47(5): 907–916. doi:10.1007/s40279-016-0638-2
- Ekstrand J, Hägglund M, Waldén M. (2011). Epidemiology of muscle injuries in professional football (soccer). The American Journal of Sports Medicine, 39(6): 1226–1232. doi:10.1177/0363546510395879
- Askling CM, Tengvar M, Thorstensson A. (2013). Acute hamstring injuries in Swedish elite football: a prospective randomised controlled clinical trial comparing two rehabilitation protocols. British Journal of Sports Medicine, 47(15): 953–959. doi:10.1136/bjsports-2013-092165
Discuss this in the forum: Nordic hamstring curls: worth it?
Hüseyin Akbulut is the founder of Sporeus and author of THRESHOLD (EŞİK), a 540-page Turkish-language book on endurance science.
- 540pp THRESHOLD Book
- MSc Sport Sciences
- Marmara University
Anatomy and Injury Mechanisms
The hamstring muscle group comprises three muscles: biceps femoris (long and short head), semitendinosus, and semimembranosus. They cross both the hip and knee, functioning to extend the hip and flex the knee, and — critically — to decelerate knee extension during the terminal swing phase…
Why Hamstrings Keep Coming Back
The recurrence problem has multiple contributing factors, several of which are modifiable through appropriate rehabilitation:
The Nordic Hamstring Curl: Prevention Evidence
The Nordic hamstring curl (NHC) is the most studied injury prevention exercise in sports medicine. The exercise involves kneeling with the feet anchored while the athlete falls forward in a controlled eccentric contraction before lowering to the ground. It produces the highest hamstring muscle activation…
Complete Rehabilitation Principles
Effective hamstring rehabilitation addresses the full spectrum of deficits rather than simply waiting for pain to resolve:
