STUDY DESIGN:Cross-sectional cohort study. BACKGROUND:Patellar tendinopathy is a load-related condition, but little is known regarding the potential differences in both biomechanical and physical activity load, measured in both laboratory and real-world environments, in individuals with and without patellar tendinopathy. OBJECTIVE:To examine differences in biomechanical and physical activity load in young male athletes with and without patellar tendinopathy. METHODS:Forty-one young male athletes (15-28 y/o) were categorized into three distinct groups: symptomatic athletes with patellar tendon abnormalities (PTA) (SYM; n=13), asymptomatic athletes with PTA (ASYM; n=14), and asymptomatic athletes without PTA (CON; n=14). Participants underwent a laboratory biomechanical jump-landing assessment and wore an accelerometer for one-week of physical activity monitoring. RESULTS:The SYM group demonstrated significantly lesser involved limb patellar tendon force loading impulse than both the CON and ASYM groups (p<0.05) with large effects (d = 0.91 - 1.40). There were no differences in physical activity between the three groups (p>0.05). CONCLUSIONS:Young male athletes with symptomatic patellar tendinopathy demonstrated lesser magnitudes of patellar tendon loading impulse during landing compared to both asymptomatic patellar tendinopathy and healthy control participants. However, these three distinct groups did not differ in general measures of physical activity. Future investigations should examine whether comprehensively monitoring various loading metrics may be valuable to avoid both under- and over-loading patterns in athletes with patellar tendinopathy. LEVEL OF EVIDENCE:Therapy, level 2b. J Orthop Sports Phys Ther, Epub 6 Jan 2020. doi:10.2519/jospt.2020.9065.