Effect of Collagen/Vitamin C in Jumper's Knee; a RCT

Inclusion Criteria: * Age 16 - 40 years old (the chosen age range will minimize chances of other conditions causing anterior knee pain such as osteoarthritis among patients above 40 years and osteochondrotic diseases like Sinding-Larsen-Johansson syndrome and Osgood-Schlatter disease among patients below the age of 16). * History of focal knee pain in patellar tendon or its patellar or tibial insertion in association with training and/or competition. * Current symptom duration of at least 12 weeks. * Sports participation at least once a week for at least one year. * Palpation tenderness to the corresponding painful area on the patellar tendon. * Focal patellar tendon pain during patellar tendon loading with a pain provocation test (single leg decline squat and/or single leg jump squat) * Victorian Institute of Sports Assessment (VISA-P) score \< 80 out of 100 points. * Willingness to take (non-vegetarian) nutritional supplements. Exclusion Criteria: * Known presence of inflammatory joint diseases (e.g. spondylarthropathy, gout or rheumatoid arthritis) or familial hypercholesterolaemia. * Daily use of drugs with a putative effect on the patellar tendon in the preceding year (e.g. fluoroquinolones and statins) * Knee surgery without a full completion of the rehabilitation program in the history of the index knee * Previous patellar tendon rupture of the index knee * Local injection therapy with corticosteroids, other drugs, blood, platelet rich plasma or stem cells in the preceding 12 months * Acute knee injuries, including patellar tendon injuries with an acute onset * Inability to perform the PTLE program * Participation in other concomitant treatment programs * Signs or symptoms of other coexisting knee pathology on physical examination (such as patellofemoral pain syndrome, joint effusion and joint line tenderness) or additional diagnostics when found necessary by the sports physician (Chondral lesion of the patella or trochlea on MRI or prepatellar bursitis on US). * Already using collagen supplementation * Giving blood donation in a period of two months prior to each test day * Being pregnant or wish to become pregnant in the upcoming year * Abuse of hard drugs * An alcohol consumption \>21 units/week (men) or \>14 units/week (women)