ACL Rehab Exercises by Phase: Evidence-Based Guide

Rehabilitation after ACL reconstruction is not a one-size-fits-all program. The exercises you do in week two look nothing like what you’ll be doing at month six, and for good reason. The healing graft goes through distinct biological phases, and every exercise must respect where the graft is in that process. At Ochsner-Andrews Sports Medicine Institute in Baton Rouge, Louisiana, the rehabilitation protocols are built around five progressive phases, each with specific goals, criteria to advance, and exercises designed to safely challenge the knee without compromising the reconstruction.

What Dr. Burnham tells every patient before surgery is this: the operation takes about an hour, but the rehab takes nine to twelve months. The surgery gives you a new ligament. The rehabilitation is what turns that ligament into a functional, sport-ready knee. The team at Ochsner-Andrews, led by Dr. Burnham in collaboration with the physical therapists and athletic trainers on his team, follows a criteria-based progression, meaning you advance to the next phase when you’ve met specific benchmarks, not simply when the calendar says it’s time.

Phase 1: Protection and Early Motion (Weeks 0 to 2)

The first two weeks after surgery focus on controlling swelling, protecting the graft, and beginning gentle range of motion. The graft is at its weakest during this period as it undergoes early ligamentization, the biological process by which the transplanted tendon begins transforming into a functional ligament. For a detailed look at what to expect each week, see the ACL surgery recovery timeline. Aggressive exercise at this stage risks stretching or damaging the graft before it has established a blood supply.

Key exercises in Phase 1: Quad sets (isometric quadriceps contractions with the leg straight), straight leg raises in all four directions (flexion, abduction, adduction, extension), ankle pumps for circulation, patellar mobilizations to prevent scar tissue from restricting kneecap movement, and passive or gravity-assisted range of motion targeting 0 degrees of extension and 90 degrees of flexion by the end of week two. Achieving full extension (getting the knee completely straight) is the single most important early goal. Losing even a few degrees of extension creates a long-term mechanical problem that is very difficult to correct later.

Criteria to advance: Full passive knee extension equal to the opposite side, flexion to at least 90 degrees, good quad activation (ability to perform a straight leg raise without an extension lag), minimal swelling, and independent walking with a normalized gait pattern (even if still using crutches for safety).

Phase 2: Restore Range of Motion and Begin Strengthening (Weeks 2 to 6)

Once the early inflammatory phase settles and the patient has achieved basic benchmarks, the focus shifts to restoring full range of motion and initiating progressive closed-chain strengthening. Closed-chain exercises (where the foot is in contact with the ground or a fixed surface) are preferred early because they load the knee in a more controlled, functional pattern and place less stress on the healing graft than open-chain movements.

Key exercises in Phase 2: Wall slides and mini squats (0 to 60 degrees), step-ups and step-downs on a low platform, stationary cycling (once flexion reaches approximately 110 degrees), leg press through a protected range, calf raises, and continued straight leg raises with progressive resistance. Prone hangs or heel prop exercises are continued to ensure full extension is maintained. Balance work begins with simple single-leg stance on a stable surface.

Criteria to advance: Full range of motion (or within 5 degrees of the opposite knee), no effusion (swelling), ability to perform a bodyweight squat to 60 degrees with good form, and normalized walking pattern without a limp.

Phase 3: Progressive Strengthening (Months 2 to 4)

Phase 3 is where the real work begins. The graft is gaining biological strength, and the focus shifts to rebuilding the quadriceps, hamstrings, and hip musculature that atrophied during the early recovery. This phase is often the most challenging for patients because the knee “feels” better than the muscles are ready for, creating a temptation to do too much too soon.

Key exercises in Phase 3: Progressive squat variations (goblet squats, split squats, Bulgarian split squats), Romanian deadlifts, leg press through increasing range, hamstring curls, hip abduction and external rotation exercises with resistance bands or cable machines, single-leg balance work on unstable surfaces (BOSU ball, foam pad), and core strengthening (planks, Pallof presses, bird dogs). Open-chain knee extension (leg extension machine) is introduced cautiously, typically from 90 to 40 degrees initially, progressing to a fuller arc as the graft matures.

Dr. Burnham’s research has shown that hip and core strengthening is not supplementary during ACL rehabilitation, it is essential. In a recent review from Dr. Burnham’s group published in the International Journal of Sports Physical Therapy, the study demonstrated that reduced hip abduction and extension strength and diminished trunk neuromuscular control predict the dynamic knee valgus patterns linked to ACL injury and re-injury. Multi-component neuromuscular programs emphasizing hip and core strengthening lower knee ligament injury rates by 20% to 60% (Burnham, Drazick, Aminake, Johnson, Ireland, Noehren, IJSPT, 2026).

Criteria to advance (3-month benchmarks from the Ochsner-Andrews ACL Center of Excellence protocol): Quadriceps limb symmetry index (LSI) at least 70%, hamstring LSI at least 70%, peak torque exceeding 160% of bodyweight (in NM/kg), ability to perform 30 single-leg squats to 100 degrees, less than 8 cm difference on Y-Balance anterior reach, full and equal range of motion, normal gait without a limp, and minimal to no effusion. These are objective thresholds, not guidelines, and each must be met before progressing to sport-specific training.

Phase 4: Sport-Specific Training (Months 4 to 6)

Phase 4 bridges the gap between general strength and the demands of sport. The graft is still maturing (the weakest biological point is typically between 3 and 6 months), so progressive loading must be carefully programmed. This phase introduces running, agility, and plyometric activities in a controlled environment.

Key exercises in Phase 4: Straight-line jogging program (beginning on a treadmill or flat surface, progressing to outdoor running), lateral shuffles and carioca drills, forward and lateral bounding, box jumps and depth jumps at low heights, single-leg hop progressions, agility ladder work, and sport-specific movement patterns (depending on the athlete’s sport). Strength training continues with increasing intensity: heavier squats, deadlifts, lunges, and single-leg exercises.

The running program is not started based on time alone. Before initiating a return-to-run protocol, the practice requires quadriceps symmetry of at least 70% on Biodex isokinetic testing, no effusion, pain-free full range of motion, and the ability to hop on the surgical leg without apprehension. Agility drills are held until quadriceps and hamstring symmetry each reach 85%, with peak torque exceeding 250% of bodyweight. Research from Dr. Burnham’s group on the hip external rotation strength hop test demonstrated that hip musculature plays a critical role in dynamic knee stability during single-leg activities, and the practice incorporates hip-focused testing before clearing patients to run (Kline, Burnham et al., KSSTA, 2017).

Criteria to advance (6-month benchmarks from the Ochsner-Andrews ACL Center of Excellence protocol): Quadriceps LSI at least 85%, hamstring LSI at least 85%, peak torque exceeding 250% of bodyweight (in NM/kg), single-leg squat test to 85% of the opposite limb, less than 4 cm difference on Y-Balance anterior reach, and a Vail Sports Cord score of 46 out of 54 or higher. The athlete must also be able to jog 20 minutes pain-free without swelling the following day, and demonstrate satisfactory performance on basic agility drills without compensation or apprehension.

Phase 5: Return to Sport (Months 6 to 12)

The final phase prepares the athlete for unrestricted return to competition. This is the phase where many athletes and even some programs rush the timeline. The practice does not. Return to sport is earned through objective testing, not calendar milestones. Every athlete must pass a comprehensive return-to-play testing battery before being cleared for full contact and competition.

Key exercises in Phase 5: Full sport-specific training at increasing intensity, reactive agility drills (unpredictable cutting and direction changes), high-level plyometrics, position-specific drills for the athlete’s sport, team practice integration (beginning with non-contact, progressing to contact), and continued maintenance strength training. The psychological component is equally important. Athletes must feel confident in the knee, not just strong.

Biodex testing data from Dr. Burnham’s group across three autograft types (quad tendon, patellar tendon, and hamstring) showed that strength recovery patterns differ by graft type (Hughes, Burnham et al., Orthop J Sports Med, 2019). Patients with quad tendon autografts demonstrated clinically meaningful quadriceps asymmetry in the early postoperative months, underscoring the need for graft-specific rehabilitation emphasis. With targeted programming, these differences resolve by the time athletes are ready for return-to-sport testing.

Why Hip and Core Exercises Are Critical Throughout

If there is one theme that runs through every phase of ACL rehabilitation, it is this: the knee does not work in isolation. The hip and trunk muscles control what happens at the knee during dynamic movement. When the hip abductors are weak, the knee collapses inward (dynamic valgus). When the trunk is unstable, the lower extremity compensates with biomechanics that load the ACL. These patterns are modifiable with targeted training, and addressing them is central to both recovery and re-injury prevention.

In Dr. Burnham’s 2026 review, the authors synthesized the evidence showing that functional assessments such as the single-leg step-down test, Y-Balance test, and belt-stabilized handheld dynamometry reliably identify high-risk athletes and persistently impaired post-ACL reconstruction patients (Burnham et al., IJSPT, 2026). Earlier work from Dr. Burnham’s group validated the role of hip external rotation strength in hop test performance after ACL reconstruction (Kline, Burnham et al., KSSTA, 2017) and demonstrated associations between hip and trunk strength and dynamic balance in uninjured populations (Wilson, Burnham et al., J Sport Rehabil, 2017).

Hip and core exercises should begin in Phase 1 (straight leg raises in abduction and extension are hip exercises) and progress through every subsequent phase. By Phase 3, dedicated hip strengthening with resistance bands, cable machines, or weight machines should be a cornerstone of the program, not an afterthought.

Return-to-Play Criteria at Ochsner-Andrews

Before clearing any athlete to return to unrestricted sport, the practice requires passage of a comprehensive testing battery. These criteria are based on published guidelines from Dr. Burnham’s group and reflect the current best evidence for safe return to play after ACL reconstruction:

Strength prerequisites (must be met before functional testing): Greater than 95% quadriceps symmetry on Biodex isokinetic testing at 60, 180, and 300 degrees per second. All three speeds must be met, as each tests a different component of muscle function: 60 deg/sec measures peak strength, 180 deg/sec measures strength-endurance, and 300 deg/sec measures explosive power and neuromuscular speed. Greater than 90% hamstring symmetry at the same speeds, greater than 90% hip abduction symmetry, and greater than 90% hip external rotation symmetry. Full range of motion, no visible effusion, and no quadriceps atrophy must also be confirmed.

Functional and hop testing (95% limb symmetry required, not attempted until 9 months post-op and all strength testing passed): Single-leg step-down at 95% of the opposite limb, single-leg squat test at 95%, Y-Balance at 95%, single-leg vertical jump at 95%, single-leg hop testing at 95%, pro-agility shuttle at 95%, timed T-test at 95%, and complete motion analysis testing.

Agility testing: Running T-test completed in under 11 seconds.

Psychological readiness: ACL-RSI (ACL Return to Sport after Injury) score greater than 75. This validated questionnaire measures an athlete’s psychological readiness to return, including confidence in the knee, fear of re-injury, and emotional response to sport. Research consistently shows that psychological readiness is one of the strongest predictors of successful return to sport and lower re-injury risk.

For complete details on the rehabilitation protocols and functional progression milestones used at Ochsner-Andrews Sports Medicine Institute, visit the protocol pages.

The Bottom Line

ACL rehabilitation is a marathon, not a sprint. Each phase builds on the last, and skipping steps or advancing too quickly is the fastest way to compromise an otherwise successful surgery. The exercises that matter most, quadriceps strengthening, hip and core work, progressive functional loading, and sport-specific training, must be done consistently, progressively, and with respect for the biology of graft healing. If you’re preparing for or recovering from ACL surgery and want a structured, evidence-based rehabilitation plan, contact the office to schedule a consultation with Dr. Burnham’s ACL program in Baton Rouge. For information on what to expect financially, see the ACL surgery cost guide. The practice treats patients from across Louisiana, including Baton Rouge, New Orleans, Lafayette, Hammond, and the surrounding Gulf South region.

References

• Burnham JM, Drazick AT, Aminake G, Johnson DL, Ireland M, Noehren BW. Current concepts in hip and core assessment to reduce the risk of ACL injury. Int J Sports Phys Ther. 2026;21(2). PMID: 41635594 | DOI: 10.26603/001c.155471
• Kline PW, Burnham JM, Yonz MC, Johnson D, Ireland ML, Noehren B. Hip external rotation strength predicts hop performance after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2018;26(4):1137-1144. PMID: 28378137 | DOI: 10.1007/s00167-017-4534-6
• Hughes JD, Burnham JM, Hirsh A, Musahl V, Fu FH, Irrgang JJ, Lynch AD. Comparison of short-term Biodex results after anatomic anterior cruciate ligament reconstruction among 3 autografts. Orthop J Sports Med. 2019;7(5):2325967119847630. PMID: 31211150 | DOI: 10.1177/2325967119847630
• Wilson BR, Burnham JM, Johnson DL, Ireland ML, Noehren B. Hip and trunk muscle strength predict dynamic balance in young female athletes. J Sport Rehabil. 2017;26(5):419-426. DOI: 10.1123/jsr.2015-0080
• Burnham JM, Yonz MC, Robertson KE, et al. Relationship of hip and trunk muscle function with single-leg step-down performance: implications for return to play screening and rehabilitation. Phys Ther Sport. 2016;22:66-73. PMID: 27592407 | DOI: 10.1016/j.ptsp.2016.05.007

Frequently Asked Questions About ACL Rehab Exercises