Importance: Following anterior cruciate ligament reconstruction (ACLR), patients often experience quadriceps muscle weakness and atrophy, frequently leading to long-term complications. A promising rehabilitation program based on blood flow restriction training (BFRT) seems to be particularly valuable for patients who may be unable to train with heavy loads due recent surgery. Previous studies have demonstrated that BFRT promotes strength gains and muscle mass increases, with adaptations comparable to traditional high-intensity training, despite using low-load resistance exercises.

Objective: to evaluate the effect of blood flow restriction training on quadriceps strength and knee biomechanics in a 4-month rehabilitation program of patients who have had an ACL reconstruction.

Design: The study will be a two-arm superiority randomized controlled clinical trial.

Setting: The trial will be conducted at a work-related injuries specialised hospital, MAZ Hospital, Zaragoza, Spain.

Participants: Participants will be active workers who have suffered an acute ACL tear and they have undergone ACL reconstruction (n=60).

Intervention: Patients will recieve a 14-16-week supervised accelerated early rehabilitation protocol; one group will complete it applying blood flow restriction training and the other will not.

Main Outcome and Measure: The primary outcomes will be peak quadriceps strength and rate of torque development measured both isometrically and isokinetcally with a Isokinetic Dynamometer CON-TREX MG.

Limitations: Potential limitations include patients and physiotherapists are not blinded.

Conclusions: The focus of the research will examine the impact of blood flow restriction rehabilitation on patients who have undergone ACLR.

Relevance: The study has potential to restore quadriceps strength to a greater extent than standard rehabilitation protocol. Moreover, patients will spend less time in the rehabilitation process to return to work compared to standard care.

Inclusion Criteria:

• Male or female (18-65 years of age); must be skeletally mature with closed physes
• Worker active
• Diagnosis of acute (<8 weeks), unilateral ACL tear with planned surgery confirmed via clinical examination and MRI
• No previous ACL injury or reconstruction on the involved limb
• Planned graft: autologous ipsilateral hamstring graft for ACL reconstruction
• Planned fixation: suspensory cortical femoral device and tibial interference screw

Exclusion Criteria:

• Completed knee dislocation or multiligament injury (PCL, MCL, LCL)
• ACL Graft diameter < 8mm
• Meniscal suture or meniscal root reattachment
• Post-surgical immobilization
• Any current or previous conditions or surgeries that might affect gait
• Pregnant
• Spinal fusion
• Any implanted medical device or other contraindications for MRI
• History of deep vein thrombosis and/or varicose veins or familiy history of deep vein thrombosis
• Taking anti-coagulant drugs for any blood, cardiac or congenital disease that may cause coagulation disorders
• Taking bone and muscle metabolism-modulation drugs or muscle supplements (e.g., creatine, amino acids, whey protein,…)
• Recent inflammation, bleeding disorders, active bleeding, or infection within the lower limbs
• Diabetic or have uncontrolled hypertension
• Diminished capacity to provide informed consent
• Unfeasible to attend regular physical therapy and study visits

Trained researchers will collect data from MAZ Hospital. All information collected during this trial will always be protected and securely stored by the lead researcher. The lead researcher will assign a secure locker in his office to store all investigation documents. Additionally, all electronic material will be safely stored and backed up on the researcher's computer equipment with a secure password.