Study on the Effects of Unilateral Resistance Training on Lower Limb Muscle Strength and Symmetry After Anterior Cruciate Ligament Reconstruction Surgery

Detailed Description This single-center, prospective, randomized controlled trial will enroll 48 patients who have undergone primary anterior cruciate ligament reconstruction (ACLR) at Chongli Campus, Peking University Third Hospital. After providing written informed consent, participants will be randomly allocated in a 1:1 ratio to either the unilateral resistance training (URT) group or the bilateral resistance training (BRT) group (24 per group).

URT: Each exercise is performed independently with one limb at a time, isolating the target limb while contralateral stabilizers are simultaneously activated to maintain balance.

BRT: Both limbs simultaneously move against a shared resistance, keeping the center of gravity stable and the movement symmetrical.

Baseline assessments will be completed within one week before the first training session; post-intervention testing will occur within three days after the final session. The program lasts six weeks, with three supervised sessions per week. Every session comprises:

5-min warm-up on a cycle ergometer 5-min core-stability work 50-min strength training (the only component that differs between groups) 10-min stretching and cool-down Six exercises are prescribed in identical order for both groups: towel-squeeze press, seated leg press, knee-extension against resistance, long-lever glute bridge, prone hamstring curl, and Romanian dead-lift. Two minutes of rest are given between sets; three minutes separate exercises. Load is set at 60 % of the relevant one-repetition maximum (1RM), re-tested at baseline and week 3 to allow progression.

URT protocol: Each exercise is executed first by the involved leg, then immediately by the uninvolved leg; completion of both sides constitutes one set. The time needed for the uninvolved leg is counted as part of the inter-set interval.

BRT protocol: Both legs work simultaneously; 1RM is determined bilaterally. Training volume, frequency, session duration, and progression criteria are therefore identical; only the resistance modality (unilateral vs bilateral) differs.

Primary outcomes are limb-symmetry indices for peak torque of knee extensors and flexors (isokinetic dynamometry). Secondary endpoints include feed-forward motor control scores, Lysholm knee scale, and IKDC 2000 subjective evaluation. All measurements are obtained pre-intervention and at week 6. The study will determine whether six weeks of URT confers superior strength recovery and inter-limb symmetry compared with conventional BRT after ACLR.

Inclusion criteria

• Age 30-55 years
• ACLR performed with hamstring-tendon autograft ≥ 3 months ago
• Full extension (no loss) and ≤ 5° difference in knee-flexion range between limbs, with flexion ≥ 120°
• Able to recruit quadriceps adequately (no lag during 10 consecutive straight-leg raises on the involved side)
• Can stand pain-free on the involved leg for ≥ 5 s without support
• Has signed informed consent and can complete all study procedures

Exclusion criteria

• Previous lower-limb surgery on either leg, including revision ACLR
• Any prior knee surgery on the contralateral limb
• Associated ligament ruptures or fractures
• Severe patellar chondral damage
• Post-operative arthrofibrosis
• Professional athletes
• Cardiac disease
• Pregnant or lactating women