The goal of this clinical trial is to see which type of strengthening exercise with a tight band (blood flow restriction) helps people recover better after ACL reconstruction. The study includes adults after ACL surgery who are doing physiotherapy to rebuild thigh muscle strength and knee function.

The main questions are:

• Does heavy strengthening with blood flow restriction improve thigh strength, knee function, and daily activities more than light strengthening with blood flow restriction after ACL surgery?
• Can light strengthening with blood flow restriction give similar benefits to heavy strengthening while putting less strain on the knee?

Researchers will compare a heavy-exercise program plus blood flow restriction to a light-exercise program plus blood flow restriction to see which gives better strength and functional improvements.

Participants will:

• Come for supervised physiotherapy sessions and do knee exercises on a machine, using either heavy or light loads while a cuff on the thigh gently squeezes to reduce blood flow.
• Have their leg strength, and knee questionnaires checked several times during the study.

This clinical trial is testing two different ways of doing strength training with a tight leg cuff (blood flow restriction) during rehabilitation after ACL reconstruction. The aim is to find out which program helps people rebuild thigh muscle strength and knee function more effectively, while still keeping the knee joint safe after surgery.

Study purpose and questions After ACL reconstruction, many people lose muscle size and strength in the front of the thigh, which can slow down recovery and delay return to sport or full activity. Blood flow restriction training allows people to train with lighter weights but still gain strength and muscle, which may be useful when heavy loads are not yet safe.

The main questions are:

• Does a heavy-load isokinetic exercise program with blood flow restriction improve thigh strength, knee function, and patient-reported outcomes more than a low-load isokinetic program with blood flow restriction?
• Can low-load isokinetic exercise with blood flow restriction provide similar benefits in strength and function, while placing less stress on the healing knee joint? Who will take part The study will include adults who have had ACL reconstruction and are in the strengthening phase of their rehabilitation. Participants will typically be active people, cleared by their surgeon and physiotherapist to start moderate to high resistance training, with no serious heart, blood vessel, or bleeding problems that would make blood flow restriction unsafe.

What happens in the study Participants will be randomly assigned to one of two groups so that each person has an equal chance of being in either group.

• One group will do heavy-load isokinetic knee exercises with a blood flow restriction cuff on the thigh.
• The other group will do low-load isokinetic knee exercises with the same type of cuff and similar exercise schedule.

Both groups will:

• Attend supervised physiotherapy sessions several times per week for around 3-4 months.
• Perform knee extension and flexion exercises on an isokinetic machine, where the speed of movement is controlled and resistance adjusts through the range of motion.
• Wear a wide cuff around the upper thigh, which is inflated to a set pressure to partially reduce blood flow out of the leg during sets, then deflated during rest periods.

The physiotherapist will adjust the load (heavy or light), cuff pressure, and number of sets and repetitions according to a fixed protocol so that each participant trains safely and progressively over time.

Measurements and outcomes

Participants will be tested at the start of the study and at follow-up visits (for example, after several weeks and at the end of the program). The main outcome is peak quadriceps strength measured on an isokinetic dynamometer. Other outcomes may include:

• Rate of torque development (how quickly the muscle can produce force).
• Functional tests such as hop tests, walking or stair tests, and timed tasks.
• Patient questionnaires about knee symptoms, daily activities, sports function, and quality of life.

Inclusion Criteria:

For ACLR group:

•Isolated unilateral ACL reconstruction 8-16 weeks post-surgery with medical clearance for moderate to high resistance training.

For control group(healthy population):

• Healthy adults with no musculoskeletal pathology.

Exclusion Criteria:

• History of cardiovascular or metabolic diseases
• Deep vein thrombosis
• Coagulopathy
• Hypertension
• Skin lesions or infections at the site of BFR cuff administration
• Neuromuscular disorders
• Non-clearance from the surgeon or physiotherapist or resistance training.