10 Key Criteria! Are You Ready To Return to Sport After ACL Surgery?

Following anterior cruciate ligament (ACL) reconstructive surgery, identifying the optimal timing for an athlete's return to sport is a crucial consideration. While the literature references both 9-month and 12-month 'time-based' return to sport guidelines, the 'criteria-based' return to sport strategy is now regarded as the most effective approach.

Kotsifaki et al (2025) conducted a study examining how rehabilitation influences the return of male athletes to pivoting sports following ACL surgery. They concluded that athletes were more likely to return to pivoting sports, if they adhered to and progressed further in their rehabilitation plan.

Ultimately, to enhance your chances of returning to sports after ACL surgery and to minimise the risk of future injury or re-injury, it is essential to:

1. Follow a structured, individualised and progressive rehabilitation programme.

2. Actually complete this rehabilitation programme, meeting all discharge criteria.

A number of the criteria outlined below assess an athlete's ability to express force (i.e. strength). Various strength qualities exist that, while distinct, do overlap with one another (6). During rehabilitation, it is essential to regularly assess an athlete's capabilities in regards to each strength quality. This approach helps to identify strengths and weaknesses, facilitating the development of effective programmes to address any deficiencies.

The following list intentionally excludes criteria concerning pain, swelling/effusion, active knee joint range of motion, and instability. These factors are continuously assessed throughout the rehabilitation process to ensure the athlete is responding positively to both gym programming and on-field rehabilitation.

Not knowing when you're ready to return to sport can be a common concern for non-professional athletes recovering from ACL reconstruction. Athletes frequently aren't informed about what 'the top of the mountain' looks like. I believe that if you know the ultimate objectives, then you're more inclined to stay committed (and actually complete rehabilitation). The following list outlines the 10 essential criteria that you must meet in order to be deemed ready to successfully return to sport. Meeting these criteria will also help to minimise the risk of re-injury.

10 Key Criteria! Are You Ready To Return to Sport After ACL Surgery? Select a criterion from the list below :

1. Knee Extension Peak Torque

2. Knee Flexion Peak Torque

3. Fast Maximal Dynamic Strength

4. Reactive Strength

5. Heavy Maximal Dynamic Strength

6. Movement Quality & Neurocognitive Considerations

7. Explosive Strength

8. Sport-Specific Fitness Profile

9. Full Unrestricted Team Training

10. Subjective Readiness Questionnaires

    
    

1. Knee Extension Peak Torque

Testing the maximal force that your quadricep muscles can express requires an isokinetic dynamometer (2). Quadricep strength deficits are commonly observed following ACL reconstruction, particularly when patella tendon or quadricep tendon grafts are used. At the 4-month mark post-surgery, we are aiming for a limb symmetry of >80%. In the late stage of rehabilitation, the target is 100% limb symmetry, with your peak torque output to be at a certain percent of your bodyweight (BW). Specifically, you're aiming for the following :

• Peak Concentric Torque (60º/s) : >260% BW (2,3)

• Peak Torque Symmetry : 100% (7)

• Inner & Outer Range Torque Symmetry : 100%

• Hamstring/Quadriceps Strength Ratio >60% (3, 7)

2. Knee Flexion Peak Torque

Testing the maximal force that your hamstring muscles can express requires an isokinetic dynamometer. Hamstring strength deficits are commonly observed following ACL reconstruction, particularly when a hamstring graft is used. An inner range hamstring strength deficit can often be observed if not targeted & addressed during rehabilitation. At the 4-month mark post-surgery, we are aiming for a limb symmetry of >80%. In the late stage of rehabilitation, the target is 100% limb symmetry, with your peak torque output to be at a certain percent of your bodyweight. Specifically, you're aiming for the following :

• Peak Concentric Torque (60º/s) : >170% BW (3)

• Peak Torque Symmetry : 100% (7)

• Inner & Outer Range Torque Symmetry : 100%

• Hamstring/Quadriceps Strength ratio > 60% (3, 7)

3. Fast Maximal Dynamic Strength

   
   

Fast maximal dynamic strength is defined as "an ability to express force maximally against no or little additional load, over somewhat quick movement times (> 0.30 seconds)" (6). One of the most commonly used tests to assess this strength quality is the countermovement jump (CMJ). Tested using force plates, a CMJ involves an athlete rapidly decelerating and accelerating their body. Restoring this physical quality is crucial for returning to field or court-based sports. During rehabilitation, deficits in both double-leg and single-leg testing are often observed (17), with a tendency to favour the unaffected limb. Metrics such as jump height, concentric impulse, and concentric/eccentric impulse asymmetry have been demonstrated to be reduced in individuals after ACL reconstruction, compared to healthy athletes (17). These deficits need to be resolved however, by the time you return to sport. Variables specific to each phase should be analysed to identify the neuromuscular strategy used to perform a jump. The target score for some variables tested, such as jump height during a CMJ, will depend on your age, sex, and sport, making it challenging to provide specific target scores for this article. Nonetheless, we aim for no more than a 5% difference between limbs across all variables. CMJ variables assessed include (4) :

• Primary Metrics :

  • Jump Height

  • Vertical Velocity at Takeoff

  • Peak Vertical Velocity

  • Relative Peak Power

• Secondary Metrics :

  • Countermovement Depth

  • Time to Take Off

  • Time to Peak Force, Velocity or Power

• Other Metrics :

  • Concentric Impulse Asymmetry (Ns, >90%)

  • Eccentric Impulse Asymmetry (Ns, >90%)

4. Reactive Strength

Reactive strength refers to the force produced during a fast stretch-shortening cycle, characterised by ground contact times of less than 250 milliseconds (5). Force plates are utilised to evaluate reactive strength, often through single and double-leg drop jump tests, as well as the 10/5 rebound jump test (RJT). Your score will provide insight into how effectively you can recruit muscle before ground contact. Restoring this physical quality is crucial for both sprinting and change of direction performance. It is common to notice deficits in single-leg testing during the rehabilitation process, but these deficits need to be resolved before you return to sports. The target score for some of the tested variables, such as the reactive strength index during a drop jump, will depend on your age, sex, and sport. This makes it challenging to specify exact target scores for this article. However, we aim for no more than a 5% difference between limbs across all variables. The key variables assessed during a drop jump include :

• Reactive Strength Index (RSI) (height / time)

  • 2-Leg RSI : >1.3

  • 1-Leg RSI : > 0.5 (both for field sport athletes) (13)

• Ground Contact Time (GCT)

• Jump Height (cm)

• Eccentric Peak Vertical Ground Reaction Force (vGRF)

5. Heavy Maximal Dynamic Strength

Five repetition max (5RM) testing can be implemented to assess an athlete's heavy maximal dynamic strength. That is, the maximal force produced by an athlete during a movement, with heavy additional load (6). An evaluation of maximal dynamic strength usually involves both an eccentric and concentric phase (4). The load lifted is recorded for each of the following exercises / movements (3) :

• Front Squat : > 1.5 BW

• 1-Leg Leg Press : > 1.5 BW

• Hip Thrust : > 1.5 BW

• Assisted 1-Leg Squat : 0.25% BW

Alongside the 5RM testing, other strength-based targets include :

• 3-5RM Split Squat : >1/3 BW

• 3-5RM Supported 1-Leg RDL : > 1/3 BW

• Trap Bar 1-Leg Landing : 1/2 BW

6. Movement Quality & Neurocognitive Considerations

Movement impairments are frequently observed following ACL surgery (15), making the restoration of movement quality critical during ACL rehabilitation (7). Video analysis is instrumental in determining how an athlete executes change of direction tasks. Despite individual movement variability, the evaluation focuses on whether the athlete aligns with an ideal technical movement model. This approach not only aids in reducing the risk of future injuries, but may also enhance performance.

Research has shown that reactive movements can adversely affect biomechanics, with varus/valgus and internal/external rotation moments being twice as high during unplanned cutting tasks, compared to pre-planned tasks (7, 14). Incorporating tests that include a reactive component (e.g. an unplanned change of direction) is therefore highly recommended, given the number of unplanned movements involved in sport.

One should also consider the impact of fatigue on both performance and testing.  Buckthorpe (2019) outlines the optimisation of late-stage ACL rehabilitation and recommends evaluating an athlete's strength and movement quality in both fatigued and non-fatigued states (7). This is because fatigue can affect neuromuscular strength and control, which can reveal movement quality deficits when testing under fatigued conditions (8).

Grooms et al (2023) indicate that neural compensation following ACL reconstruction is evident via increased attention to movements that athletes previously performed instinctively (16). Therefore, the authors suggest performing return to sport testing that includes combined neurocognitive and motor dual-task challenges. This will assess the athlete's degree of neurocognitive reliance. Metrics of neurocognitive ability include reaction time / response time, online working memory, gaze control and visual-spatial attention (16).

The tests related to this criterion should be specific to the movement patterns commonly observed in the athlete's sport. However, some examples include :

• Deceleration Tasks

  • Metrics : Completion time (s), GCT (ms), Knee angle at initial contact (deg), Change in trunk angle (deg)

• Change of Direction Tasks

  • Planned & Unplanned 90-degree & 180-degree Cuts

    • Metrics : Completion time (s), GCT (ms), hGRF : vGRF (N/kg), Knee angle at initial contact (deg)

    • Observation : low COM, shortened step length, trunk orientated in the direction of intended travel

• Combined neurocognitive and motor dual-task challenges (<10% deficit)

  • Neurocognitive Hop Test Battery

  • Field-based Neurocognitive Tests

7. Explosive Strength

The capacity to rapidly generate force is crucial, as numerous athletic activities, including sprinting and jumping, are subject to time constraints. The ability to produce force rapidly can be measured as rate of force development (RFD) (i.e. change in force / change in time) (18). Reporting RFD over specific intervals (0-50, 50-100, and 100-150 ms) is considered to offer a more reliable measure and a clearer understanding of the determinants of RFD (9, 10). With ACL ruptures occurring approximately 50 milliseconds following ground contact (10), restoring an athlete's ability to express force rapidly (i.e. early RFD or <100ms) prior to returning to sport, is key in mitigating future injury risk. Deficiencies in RFD are frequently observed following ACL reconstructive surgery. It has also been reported that fatigue affects the RFD more quickly and profoundly than it affects maximal force production, particularly in the initial 50 milliseconds of contraction (11). This highlights the need to restore RFD before resuming sports activities. According to Maffiuletti et al (2016), rigorous methodological procedures are essential, especially when assessing early RFD, due to its lower reliability compared to maximal isometric strength testing (18). The evaluation of RFD during ACL rehabilitation could include the following :

• Single-Joint Isometric Testing

  • Knee Flexion & Extension - Early & Late RFD (LSI > 90%)

    • Under Both Fresh & Fatigued Conditions

    • At Specific Joint Angles

• Multi-Joint Isometric Testing

  • Isometric Squat or IMTP - Early & Late RFD (LSI > 90%)

8. Sport-Specific Fitness Profile

It is vital that an athlete restores their sport-specific fitness profile during the late stage of ACL rehabilitation (7). In order words, are they prepared for the physical demands that full training sessions and games entail? The physical profile of an athlete will vary between sports (e.g. field hockey v's rugby), playing positions (e.g. defender v's midfielder), gender and playing level (7). One should consider the number of high-intensity deceleration, acceleration and changes of direction that an athlete commonly performs in their sport. The total distance covered during a game, along with the number of high-intensity running meters, will determine the energy system contributions. The literature on time-motion analysis should be employed to inform pitch-based training sessions, starting with the end-goal of meeting match-day physical demands and working backward from there.

Sports-specific physical testing examples include (7).:

• Yo-Yo intermittent recovery test (aerobic & anaerobic system capacity)

• T-Test (change of direction ability)

• 10-30m acceleration

• Maximal Velocity (using GPS Data)

9. Full Unrestricted Team Training

The return to sport process should involve a gradual progression from 'on-field / on-court rehabilitation' (OFR) to 'return to team training', though to 'return to competition' (5). Ultimately, the aim is to guide the athlete back to training safely in the best physical condition to cope with the demands of their chosen sport (5). Utilising GPS (StatSports) and heart rate monitoring (Polar) are key to ensuring that an athlete is progressively building towards the volume and intensity that they will experience during team training sessions and games. On-field rehabilitation starts with one-on-one training sessions, but it's crucial for an athlete to eventually participate in full team trainings. Engaging in team training sessions will not only replicate the intensity of game day but also improve the athlete's psychological readiness. Picinini et al. (2025) reported high rates of return to competition among amateur and professional soccer players who underwent on-field rehabilitation, following ACL surgery (12). Of concern, the authors noted that 43% of players did not reach stage 5 of OFR, stopping at earlier stages, and therefore not completing rehabilitation. In conclusion, completing all 5-stages of OFR is non-negotiable. Think about it. Why would you put in so much effort over months and months in the gym, to then just skip a key phase of rehabilitation.

10. Subjective Readiness Questionnaires

In addition to evaluating all the physical criteria mentioned above, assessing the athlete's psychological readiness is equally crucial. Completing various questionnaires can help identify a lack of confidence or fear of re-injury. One's physical function has the capacity to influence their psychological status following ACL surgery (5). Similar to preparing for a school exam, if you have dedicated time and effort, you will perform excellently. The same applies to ACL rehabilitation. Consistent and progressive work throughout rehabilitation will lead to success in the three questionnaires at the end. The three questionnaires are :

• ACL-RSI Questionnaire (Psychological Readiness) : >90%

• IKDC (Self-Reported Knee Function) : >90%

• I-PRRS (Psychological Readiness) : >50

Conclusion

A 'criteria-based' return to sport strategy is regarded as the most effective approach during ACL rehabilitation (1, 7). Adherence and progressing deep into the rehabilitation plan, along with completing on-field / on-court rehabilitation are keys to a successful outcome. There is no optimal or perfect testing procedure to determine one's readiness to return to sport (7), so we depend on the latest literature and expert consensus to inform decision making.

Restoring the neuromuscular elements that affect movement quality is a fundamental prerequisite before returning to sports. This process involves successfully passing isokinetic peak torque assessments for both the quadriceps and hamstrings, as well as restoring rate of force development (RFD), rapid maximal dynamic strength, heavy maximal dynamic strength and reactive strength. Return-to-sport evaluations should incorporate combined neurocognitive and motor dual-task challenges to assess the athlete's level of neurocognitive reliance. Additionally, it is essential for the athlete to reestablish their sport-specific fitness profile, in order to adequately prepare for the demands of competition.

Remember, you are six times more likely to return to pivoting sports by meeting your discharge criteria, compared to those athlete's who stop rehabilitation early (1). Returning to sport without fulfilling each criterion may also increase the risk of re-injury or other injuries. This post outlines 10 key criteria to help an athlete successfully return to sport following ACL surgery.

If you aren't sure where you stand physically following ACL surgery, you haven't returned to sport yet, or you're just not confident that you can deal with the physical demands of sport just yet, then drop me a message for a discussion (info@buanphysio.ie).

References

(1) Kotsifaki R, King E, Bahr R, et al. (2025). Is 9 months the sweet spot for male athletes to return to sport after anterior cruciate ligament reconstruction? British Journal of Sports Medicine. doi: 10.1136/bjsports-2024-108733

(2) Wilk KE, Arrigo CA, Davies GJ. Isokinetic Testing: Why it is More Important Today than Ever. IJSPT. 2024;19(4):374-380. doi:10.26603/001c.95038

(3) Santry Sport Clinic. ACL Reconstruction Rehabilitation Guidelines. Bone-Patellar Tendon-Bone (BPTB)

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