ABSTRACT

Hamstring strains and anterior cruciate ligament (ACL) injuries are among the most prevalent and impactful musculoskeletal injuries in athletic populations, often resulting in significant time loss, reduced performance, and high rates of recurrence. Effective management extends beyond treatment alone and requires an integrated approach combining injury prevention strategies, structured rehabilitation, and evidence-based return-to-sport criteria. Eccentric strengthening interventions such as the Nordic Hamstring Exercise, alongside neuromuscular training programs targeting movement quality, have demonstrated substantial reductions in injury incidence. Rehabilitation must be progressive and criteria-driven, emphasizing restoration of strength, neuromuscular control, and psychological readiness. This article examines current evidence surrounding prevention, rehabilitation phases, and re-injury mitigation strategies for hamstring and ACL injuries, highlighting the importance of comprehensive, multidisciplinary approaches to optimize athlete outcomes and long-term performance.

KEY POINTS

• Hamstring strains and ACL injuries carry high recurrence rates, emphasizing the need for structured prevention and rehabilitation.

• The Nordic Hamstring Exercise (NHE) can reduce hamstring injury risk by up to 51%.

• Neuromuscular training programs significantly decrease ACL injury risk, particularly in youth athletes.

• Rehabilitation should follow phased, criteria-based progression, not time alone.

• Return-to-sport decisions should include strength symmetry, functional testing, movement quality, and psychological readiness.

• Delaying ACL return to sport until ≥9 months significantly reduces re-injury risk.

INTRODUCTION

Athletes at all levels are prone to musculoskeletal injuries, with hamstring strains and anterior cruciate ligament (ACL) tears being among the most common and debilitating. Hamstring strains often afflict sprinters, soccer players, and other athletes who perform high-speed running or kicking, whereas ACL injuries frequently occur in pivoting sports like basketball, football, and soccer. Beyond the immediate pain and time lost, these injuries carry a high risk of recurrence if not managed properly. Approximately one-third of hamstring strains recur within the first year after return to play, and recurrent hamstring injuries tend to be more severe than the initial injury (Erickson & Sherry, 2017). Similarly, young athletes who return to sport after an ACL reconstruction face about a 23% chance of sustaining a second ACL injury, underscoring the need for robust prevention and rehabilitation strategies (Wiggins et al., 2016). This article discusses evidence-based approaches to prevent hamstring and ACL injuries, outlines key rehabilitation phases, and examines strategies to reduce re-injury risk.

HAMSTRING STRAIN PREVENTION STRATEGIES

The Nordic Hamstring Exercise (NHE) — a partner-assisted or anchored eccentric exercise — significantly reduces strain incidence. An umbrella review found teams implementing NHE experienced up to a 51% reduction in hamstring injuries (Nunes et al., 2024). Improved eccentric strength and muscle fascicle length contribute to resilience during sprinting and kicking. Coaches typically integrate 1–2 sets of 5–10 reps, 2–3x per week in preseason, maintaining throughout the season.

Warm-ups that include dynamic stretching, acceleration drills, and neuromuscular training also support prevention. Fatigue management — reducing high-speed loads without recovery — is vital to lowering risk.

Hamstring strain prevention has advanced with research on eccentric strengthening exercises. One standout intervention is the Nordic Hamstring Exercise (NHE), in which a partner or device anchors the athlete’s ankles as they slowly lean forward from a kneeling position, loading the hamstrings eccentrically. Injury prevention programs incorporating NHE have been shown to significantly reduce hamstring strain incidence. A recent umbrella review reported that teams adding NHE to training experienced up to a 51% lower rate of hamstring injuries compared to controls (Nunes et al., 2024). In soccer players specifically, the pooled data indicated roughly half the risk of hamstring strains in those performing NHE routines versus those who did not. These benefits are attributed to improved eccentric strength and longer muscle fascicle lengths in the hamstrings, which enhance the muscle’s resilience during high-speed movements (Nunes et al., 2024). Practical example: Many professional soccer clubs have implemented NHE in warm-ups; as a result, they have observed fewer mid-season hamstring pulls. Coaches are advised to progressively introduce NHE (e.g. 1–2 sets of 5–10 reps, 2–3 times weekly in preseason) and continue maintenance doses during the season (Nunes et al., 2024).

Besides NHE, comprehensive warm-up routines and flexibility programs play a role. Dynamic stretching and agility drills before training help increase muscle temperature and pliability, potentially lowering strain risk. Eccentric hamstring curls, bridging exercises, and sport-specific drills that mimic sprinting or kicking motions can also build hamstring robustness. Some studies note that inadequate fatigue management (e.g. high sprint loads without recovery) is a risk factor, so monitoring training load is important. In practice, an integrated injury prevention program may combine NHE, agility and trunk stabilization exercises, and proper load management to maximize hamstring injury prevention (Erickson & Sherry, 2017).

REHABILITATION AND RECOVERY PHASES FOR HAMSTRING STRAINS

When a hamstring strain does occur, a structured rehabilitation program is critical to promote healing and minimize downtime. Rehab is typically divided into phases with specific goals (Erickson & Sherry, 2017):

• Phase 1 – Acute Phase: Focus on managing pain, inflammation, and protecting the injured muscle. This includes rest from aggravating activities, gentle range-of-motion exercises, and isometric contractions. Avoiding excessive stretching of the hamstring early on is important to allow torn fibers to begin repairing (Erickson & Sherry, 2017). Light neuromuscular exercises (e.g. glute bridges, core stability work) can be introduced to maintain hip and trunk function without stressing the hamstring.

• Phase 2 – Subacute/Reconditioning: As pain subsides, the athlete progresses to restoring strength and mobility. Eccentric strengthening is introduced in a controlled manner (for example, light Nordic curls or slider curls) alongside more dynamic movements at moderate speed (Erickson & Sherry, 2017). Neuromuscular training drills (such as single-leg balance, hip extension movements, and light jogging) at gradually increasing speeds are included. The goal is to safely rebuild hamstring tensile strength and coordination.

• Phase 3 – Advanced Training: Emphasis on high-speed neuromuscular training, sport-specific drills, and eccentric loading at longer muscle lengths (Erickson & Sherry, 2017). Exercises like bounding, sprinting, and cutting are reintroduced as tolerated. The hamstring is loaded in elongated positions (e.g. Romanian deadlifts, Nordic curls at greater lean angles) to prepare it for the stretch during maximal sprints. This phase also includes functional testing to evaluate readiness, such as pain-free maximal sprints, deceleration drills, and hamstring strength at least 90% of the uninjured side.

REDUCING HAMSTRING RE-INJURY RISK

Re-injury prevention is a paramount concern, given the high recurrence rate for hamstring strains. Research suggests many recurrences stem from insufficient rehabilitation or a too-hasty return to play (Erickson & Sherry, 2017). To combat this, clinicians use objective return-to-play criteria. Key criteria include: no pain or tenderness on palpation of the injury site, full range of motion and strength equal to the opposite leg, and the ability to perform sport-specific actions at full intensity without discomfort (Erickson & Sherry, 2017). Notably, athletes who still had mild hamstring pain on palpation at return were found to be nearly four times more likely to suffer a re-injury (Erickson & Sherry, 2017). Therefore, complete resolution of local tenderness is a critical checkpoint.

A holistic rehab program also addresses contributing factors to hamstring injuries. Strength imbalances between the hamstrings and quadriceps are corrected with targeted strength training (eccentric hamstring work to improve the hamstring-to-quadriceps strength ratio) (Erickson & Sherry, 2017). Core and pelvic stability are incorporated: exercises that improve lumbopelvic control (planks, side bridges, stability ball drills) can optimize hamstring function during running (Erickson & Sherry, 2017). In fact, one clinical trial found that adding progressive agility and trunk stabilization (PATS) exercises to rehab resulted in dramatically lower recurrence rates (only ~8% re-injured) compared to a standard hamstring stretching and strengthening program (~70% re-injured) over one year (Erickson & Sherry, 2017). This underscores how trunk stabilization and agility training enhance neuromuscular control, reducing risky compensations that could predispose to re-injury.

Psychological readiness is also considered. Athletes may have anxiety about re-injury, which can alter their movement patterns. Ensuring the athlete has confidence in their hamstring through gradual exposure to high-speed running and providing education about the injury can alleviate fear. By Phase 3, the athlete ideally has performed near-maximal sprints and sport drills in practice, building trust that the muscle can handle competition demands.

Finally, a gradual return-to-play plan is essential. Rather than full competition immediately, the athlete might first participate in modified training, then limited minutes or non-critical roles in a game, before returning to full play. Ongoing maintenance exercises (like periodic NHE sessions and core work) should continue after return to sport to maintain the muscle’s resilience (Erickson & Sherry, 2017).

ACL INJURY PREVENTION STRATEGIES

ACL injuries often occur from sudden deceleration, cutting, or awkward landings that place high stress on the knee. Prevention programs have proven effective, especially in young athletes. Comprehensive neuromuscular training (NMT) that teaches proper landing and cutting technique, builds lower-body strength, and improves balance can significantly reduce ACL injury rates (Petushek et al., 2019). For example, structured warm-up programs like FIFA 11+ or PEP (Prevent Injury and Enhance Performance) incorporate jumping exercises, agility drills, and strength work. A systematic review of such programs found an overall halving of ACL injury risk – one meta-analysis noted NMT lowered the odds of ACL tears by about 49% (OR ~0.51) in female youth athletes (Petushek et al., 2019). The greatest benefits were seen when training was targeted to high-risk groups (e.g. adolescent female soccer and basketball players) and done consistently (at least 2–3 times per week during season) (Petushek et al., 2019). Key elements include plyometrics with proper technique (teaching athletes to land softly on the balls of the feet with knees bent and not collapsing inward), strengthening of hamstrings and glutes (to help stabilize the knee), and balance/proprioception drills (e.g. single-leg balance on unstable surfaces).

The inclusion of exercises like lunges, single-leg squats, and Nordic hamstring curls in ACL prevention routines is specifically recommended (Petushek et al., 2019). Strong hamstrings can help resist the anterior tibial translation that stresses the ACL, and NHE, as noted earlier, strengthens hamstrings eccentrically. An example from practice: youth basketball teams that adopted a 15-minute neuromuscular warm-up (including jumping and core drills) have reported fewer knee injuries compared to teams without such a program, illustrating how prevention can be translated to the field.

Another crucial strategy is training athletes in cutting technique – encouraging deceleration off both legs, lowering the center of gravity, and avoiding severe inward knee buckling (valgus) during changes of direction. Coaches can incorporate shuttle drills and zig-zag runs focusing on safe mechanics. Given that fatigue can degrade technique, conditioning drills should include form cues even when athletes are tired.

REHABILITATION AND PHASES OF RECOVERY FOR ACL INJURIES

Recovering from an ACL reconstruction (ACLR) typically spans 9 to 12 months or more, and follows a phased approach:

• Early Post-Op (Weeks 0–6): Goals are to protect the surgical graft, reduce swelling, restore knee range of motion (especially full extension), and activate the quadriceps muscle. Exercises include gentle range of motion (heel slides, stationary cycling with no resistance), quadriceps sets and straight-leg raises (to address post-surgery quad inhibition), and gait training to normalize walking. Emphasis on patellar mobility and achieving full knee extension by a few weeks post-op helps prevent motion deficits (Erickson & Sherry, 2017).

• Strengthening and Neuromuscular Training (Months 2–5): As healing progresses, more intensive strengthening is introduced. This includes closed-chain exercises like squats, step-ups, and leg press to build quadriceps and gluteal strength while minimizing knee joint strain. Hamstring strengthening (especially if a hamstring tendon graft was used) is also incorporated. Proprioceptive exercises (balance boards, single-leg stands, perturbation training) help the athlete relearn joint position sense. By 3–4 months, light jogging may begin if strength and mechanics are appropriate. The focus is on achieving symmetric strength between legs and improving movement quality – e.g., ensuring no knee collapse on single-leg squats. Criteria often used around the 4–6 month mark include at least 70%–80% strength of the uninvolved leg in quads and hamstrings and the ability to hop in place or on a single leg without pain.

• Advanced Training (Months 6+): In this phase, the athlete works on power, agility, and sport-specific tasks. Plyometric drills (jumping and hopping) are progressed gradually: starting with double-leg hops and advancing to single-leg hops and bounding. Cutting and acceleration/deceleration drills are reintroduced, first at half-speed and then increasing to game intensity. A return-to-sport test battery is typically administered when nearing return. This battery often includes isokinetic strength testing of the quadriceps and hamstrings, and functional hop tests (e.g. single hop for distance, triple hop, crossover hop, and 6-meter timed hop) (Grindem et al., 2016). Many sports medicine programs use a threshold of 90% limb symmetry or better on these metrics as a criterion for clearance – meaning the injured leg performs at least 90% as well as the uninjured leg on strength and hop measures (Grindem et al., 2016). For example, an athlete should be able to broad-jump just as far on the repaired leg as on the healthy leg. Achieving this symmetry indicates the muscle strength and power have been largely restored.

• Return-to-Play Integration (Month 9 and beyond): Even after meeting clinical criteria, athletes are often advised to gradually reintegrate into full competition. This may involve unrestricted practice sessions first, then limited play time, before full return. Research suggests that waiting at least 9 months post-ACLR before returning to high-risk sports dramatically lowers re-injury risk (Grindem et al., 2016). In fact, one cohort study found that for each month return to sport was delayed up to 9 months, the re-injury rate dropped by 51% (Grindem et al., 2016). Athletes who returned before 9 months had a several-fold higher risk of re-tearing the ACL graft or tearing the ACL in the other knee. Therefore, enforcing a minimum rehab duration (around 9–12 months depending on age and sport) along with objective criteria is considered best practice.

RE-INJURY RISK AND MITIGATION IN ACL

Returning to sport after an ACL injury is a stepwise process that balances the desire to play with the risk of re-injury. Re-injury rates for ACL are concerning – studies of young athletes show roughly 1 in 4 will suffer a second ACL tear (either graft retear or opposite knee) after returning to sports like football or soccer (Wiggins et al., 2016).  Notably, most of these second injuries occur early in the return period, when the athlete is back to full competition exposure for the first time in many months (Wiggins et al., 2016). This statistic underpins the importance of stringent return-to-play criteria and shared decision-making (involving surgeons, therapists, coaches, and the athlete) about when it is safe to go back.

Objective criteria as mentioned (90% strength and hop performance) are one pillar. Another pillar is ensuring the athlete has recovered fundamental movement quality. Motion analysis or trained observers will look for signs of poor mechanics – for instance, during a single-leg squat or jump landing, does the athlete exhibit knee valgus (inward collapse) or asymmetrical weight distribution? A consensus group of experts has suggested that a return-to-sport test battery should also include qualitative assessment of movement technique, not just quantitative measures (Ardern et al., 2016). If an athlete demonstrates unsafe movement patterns, additional neuromuscular training is prescribed to correct those before return.

Psychological readiness is equally vital. After a long rehab, athletes may have fear of re-injury or lack confidence in the knee. This can manifest as hesitancy in movements or avoidance of certain plays. Paradoxically, fear can increase injury risk by causing suboptimal technique (for example, landing stiffly due to worry about the knee). Surveys have identified fear of re-injury as a leading reason athletes fail to return to their prior level of sport (Sheean et al., 2023). Thus modern rehab includes psychological support: setting realistic expectations, mental imagery of successful performance, and sometimes formal mental skills training. Tools like the ACL-Return to Sport Index (ACL-RSI) questionnaire measure psychological readiness; a low score might prompt interventions such as guided gradual exposure to sport drills to build confidence. Example: A collegiate gymnast might be initially afraid to do landings off an apparatus after ACL surgery. The therapist can slowly reintroduce small hops, then drops from a low height, gradually increasing challenge. As the athlete completes each without pain or failure, confidence grows. In some cases, consulting a sports psychologist can help address lingering anxiety or trust issues in the knee.

REAL-WORLD EXAMPLE AND BEST PRACTICE

Consider the case of a soccer player recovering from ACL reconstruction. At six months post-op, she has excellent quadriceps strength and can run straight ahead, but during lateral shuffle and cut drills, her therapist notices knee instability and the athlete admits she “doesn’t trust” the knee yet. The rehab team keeps her in the training phase for an additional two months, focusing on lateral agility drills, improving hip muscle strength, and doing scenarios where she has to react to a defender. They also have her practice with a brace initially to provide mental and physical support. At nine months, she passes all hop tests at >95% symmetry and reports no apprehension in full-contact practice. By waiting and ensuring all criteria are met, the athlete reduces her re-injury risk. Research supports this approach: one study showed athletes who passed a return-to-sport battery (including strength and hop tests) had a much lower ACL re-injury rate (~5.6%) than those who failed to meet criteria (~38% re-injured) (Grindem et al., 2016). Although not every athlete with ideal metrics will avoid injury, the odds improve substantially with rigorous criteria.

CONCLUSION

Preventing and rehabilitating hamstring and ACL injuries requires a multifaceted, evidence-based strategy. For hamstrings, incorporating eccentric strengthening exercises like Nordic curls, ensuring comprehensive rehab (addressing strength, flexibility, core stability, and gradual return), and adhering to return-to-play guidelines can cut injury rates and recurrences dramatically. For ACL injuries, neuromuscular training programs are proven to lower risk, and a criteria-driven, phased rehab approach is essential to optimize outcomes. Across both injury types, education and athlete buy-in are key – athletes should understand that rushing back too soon or skipping rehab steps can have long-term consequences. By using peer-reviewed sports medicine research to guide prevention (e.g. 50% injury reductions with the right exercise programs) (Petushek et al., 2019). and by implementing strict return-to-play criteria, coaches and clinicians can help athletes stay healthy and perform at their best. Ultimately, a combination of smart training, dedicated rehabilitation, and collaborative decision-making forms the cornerstone of injury prevention and successful recovery for hamstring and ACL injuries.

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