ACL Rehabilitation and Returning to Sports: Why Testing Matters More Than the Calendar
An ACL reconstruction (ACLR) is only the beginning of an athlete’s journey back to sport. The goal of rehabilitation is not simply to reach a certain number of months after surgery—it is to restore the strength, power, movement quality, confidence, and sport-specific capacity needed to safely perform at a high level.
One of the biggest misconceptions following ACL reconstruction is that every athlete should follow the exact same timeline. Not everyone's recovery looks the same. Graft type, associated meniscus or cartilage procedures, age, sport, position, strength deficits, previous injury history, rehabilitation consistency, and psychological readiness can all influence the recovery process.
For this reason, return-to-sport (RTS) decisions should be criterion-based rather than based on time alone.
Why Return-to-Sport Testing Matters
Research continues to demonstrate that athletes can have meaningful deficits even when they are considered ready to return to sport. A 2024 systematic review found that athletes demonstrated functional deficits at RTS testing an average of 7.9 months after ACL reconstruction. Quadriceps strength was particularly concerning: 10 of 17 studies reported average quadriceps limb symmetry below 90%.¹
This is why simply saying, “You're nine months out, so you're cleared,” is not enough.
A thorough RTS assessment should examine multiple components of performance, including strength, power, balance, movement quality, functional capacity, and psychological readiness.
Quadriceps Strength: Isometric vs. Isokinetic Testing
Quadriceps strength is one of the most important pieces of an ACL rehabilitation assessment. Strength can be measured in several ways, but isometric and isokinetic testing provide different types of information.
Isometric quadriceps testing measures how much force an athlete can produce while the knee remains at a fixed joint angle. There is no visible movement of the knee during the test. A handheld dynamometer can be used to objectively measure peak force, making isometric testing relatively accessible in a physical therapy setting.
Isokinetic testing, on the other hand, measures muscle performance while the joint is moving at a predetermined constant angular velocity. Specialized equipment controls the speed of movement while the athlete produces maximal effort. Isokinetic testing can provide information such as peak torque and work at different speeds and is frequently used as a reference standard in ACL research.²
Both tests have value. Isometric testing is practical, repeatable, and can be performed with relatively minimal equipment, while isokinetic testing provides a more detailed assessment of muscle performance across a range of motion and velocities.
A commonly used RTS benchmark is ≥90% limb symmetry index (LSI) when comparing the involved and uninvolved legs. However, symmetry should not be the only consideration. An athlete can achieve 90% symmetry if both legs are significantly weaker than they should be. Absolute strength, strength relative to body weight, sport demands, and comparison with normative data should also be considered.³
Hop and Single-Leg Jump Testing
Hop testing evaluates single-leg power, force production, landing control, coordination, and confidence. A comprehensive battery may include:
Single-leg hop for distance
Triple hop for distance
Crossover hop
6-meter timed hop
Single-leg vertical jump
Repeated or reactive jumping
Again, ≥90% LSI is commonly used as a benchmark, but the quality of movement matters just as much as the number.
Recent research has shown that hop performance can improve substantially during rehabilitation but may still remain below the level of an uninjured athlete.⁴ Additionally, hop and strength tests should not be used in isolation to determine whether an athlete is ready to return to sport. Recent systematic reviews have found that commonly used RTS tests have inconsistent ability to predict reinjury when used individually or even as a combined battery.⁵
Balance, Movement Quality, and Y-Balance
The Y-Balance Test can provide additional information about single-leg balance, reach control, and neuromuscular control. It can be particularly useful when interpreted alongside strength and functional testing.
An athlete should also be assessed during tasks such as:
Single-leg squatting
Jumping and landing
Deceleration
Cutting and change of direction
Lateral movement
Repeated jumping
Reactive or unanticipated movements
These assessments can identify movement deficits that may not appear during isolated strength testing.
Psychological Readiness Matters, Too
Returning physically is only part of the equation. Athletes also need to feel prepared to trust their knee and perform without excessive fear or hesitation.
Patient-reported measures such as the ACL-Return to Sport after Injury (ACL-RSI) can help evaluate confidence, emotions, and fear surrounding a return to sport. Current literature supports incorporating psychological readiness into a broader RTS decision rather than relying solely on physical testing.³
You Don't Need a High-Tech Lab
The good news is that many meaningful RTS tests can be performed with minimal technology or equipment.
While force plates, motion-capture systems, and isokinetic machines can provide valuable information, a comprehensive clinical assessment can still include a handheld dynamometer, measuring tape, stopwatch, Y-Balance equipment, and adequate space for jumping and running.
The most important factor is not having the most expensive technology. It is selecting appropriate tests, performing them consistently, and interpreting the results within the context of the individual athlete.
Returning to Sport Is a Progression—Not a Single Day
Passing an RTS test does not necessarily mean an athlete should immediately play an entire game.
A successful return should progress from:
Rehabilitation → Running → Jumping/Landing → Agility → Non-contact Practice → Controlled Contact → Full Practice → Limited Competition → Full Competition
This gradual progression allows the athlete to rebuild exposure to the acceleration, deceleration, cutting, contact, fatigue, and decision-making demands of their sport.
Ultimately, there is no single test and no single timeline that determines when an athlete is ready to return after ACL reconstruction. A thorough assessment should combine objective quadriceps strength testing, hop and single-leg jump performance, balance, movement quality, sport-specific testing, and psychological readiness.
The goal is not simply to get an athlete “cleared.” The goal is to help them earn their return and confidently handle the demands of their sport.
Your ACL recovery should be based on what your knee can do—not just how long it has been since surgery.
Helpful Equipment for the Later Stages of ACL Rehabilitation
For athletes working through the strength, balance, and power phases of rehabilitation, some relatively simple equipment can be useful at home. These should supplement—not replace—a rehabilitation program prescribed by a physical therapist.
Important: Patients should not begin maximal jumping, hopping, cutting, or other high-level ACL exercises simply because they have purchased the equipment. The appropriate timing, intensity, and progression should be determined by their rehabilitation team.
References
Gill VS, Haglin JM, Marks L, Tokish JM. Athletes continue to show functional performance deficits at return to sport after anterior cruciate ligament reconstruction: a systematic review. Arthroscopy. 2024;40(8):2247-2261. doi:10.1016/j.arthro.2023.12.033. (PubMed)
Kotsifaki R, Van Rossom S, Whiteley R, et al. Evidence for isokinetic and functional testing in return to sport decisions following ACL surgery. PM R. 2022;14(7):903-913. doi:10.1002/pmrj.12614. (PubMed)
Kotsifaki R, Korakakis V, King E, et al. Return to sport following anterior cruciate ligament reconstruction: a scoping review of criteria determining return to sport readiness. Sports Med. 2025;55:??. (PubMed Central (PMC))
King E, Richter C, Franklyn-Miller A, et al. Hop to it! A systematic review and longitudinal meta-analysis of hop performance after ACL reconstruction. Sports Med. 2024;54:??. doi:10.1007/s40279-024-02121-1. (PubMed)
Gill VS, Haglin JM, Marks L, Tokish JM. Functional return-to-sport testing demonstrates inconsistency in predicting short-term outcomes following anterior cruciate ligament reconstruction: a systematic review. Arthroscopy. 2024;40(7):2135-2151.e2. doi:10.1016/j.arthro.2023.12.032. (Arthroscopy Journal)
Nawasreh Z, Adams G, Logerstedt D, et al. Test batteries after primary anterior cruciate ligament reconstruction: a systematic review. Sports Health. 2022;14(2):235-243. (PubMed Central (PMC))
