This randomized controlled trial compares blood flow restriction (BFR) resistance training (leg press and seated knee extension at 30% 1RM) versus BFR cycling (stationary cycling at low resistance) in 60 athletes (aged 18-40 years) diagnosed with patellofemoral pain syndrome. Both interventions are delivered over 8 weeks (3 sessions/week) with a pneumatic cuff set at 80% limb occlusion pressure. Primary outcomes include pain intensity (NPRS), quadriceps strength (handheld dynamometer), and functional ability (Kujala Anterior Knee Pain Scale), assessed at baseline and post-intervention.

Patellofemoral pain (PFP) is among the most prevalent musculoskeletal conditions in athletes, with reported prevalence of 30-40% in sports populations. High-load resistance training is the conventional rehabilitation approach but often exacerbates joint stress and reduces adherence. Blood flow restriction (BFR) training enables strength gains at low loads by applying a pneumatic cuff at 80% LOP on the proximal thigh.

This trial compares two BFR modalities:

• Group A (BFR-RT): Leg press and seated knee extension, 1x30 + 3x15 reps at 30% 1RM, 3x/week for 8 weeks.
• Group B (BFR-CYC): Stationary cycling at low resistance, 4x5-minute intervals at 70-80 RPM (RPE 11-13), 3x/week for 8 weeks.

All sessions are supervised one-on-one by a physiotherapist. Assessments are conducted at baseline and week 8. The study is single-blinded (outcome assessor blinded). Randomization via computer-generated sequence. Statistical analysis via SPSS v27 (paired t-test / Wilcoxon for within-group; independent t-test / Mann-Whitney for between-group, alpha=0.05).

Inclusion Criteria:

1. Male and female athletes aged 18-40 years
2. Clinically diagnosed with patellofemoral pain syndrome
3. Anterior or retropatellar knee pain of at least 3 months duration
4. Pain provoked by at least two functional activities (e.g., squatting, stair climbing, running, prolonged sitting)
5. Willingness to participate and provide written informed consent

Exclusion Criteria:

1. History of knee surgery or significant knee trauma in the past 6 months
2. Presence of ligament, meniscal, or cartilage injuries
3. Neurological, vascular, or systemic inflammatory conditions
4. Contraindications to BFR training (e.g., deep vein thrombosis, uncontrolled hypertension)
5. Pregnancy

This is a single-blinded study in which the outcome assessor is blinded to group allocation. Participants and treating physiotherapists are aware of the assigned intervention due to the nature of exercise-based rehabilitation. Efforts are made to standardize instructions and interaction across both groups to minimize bias.