The TRAjectory of knee heaLth in runners (TRAIL) study is a prospective cohort study investigating the long-term knee health trajectories of runners with and without a heightened osteoarthritis risk. This study aims to describe the recruitment results and baseline characteristics of the TRAIL cohort.

Runners aged 18–50 years and running ≥3 times and ≥10 km per week on average in the past 6 months were eligible. Participants were recruited via running podcasts, running clubs and social media between July 2020 and August 2023. Data were collected at study enrolment and at a face-to-face baseline testing session, which occurred a median of 33 weeks (IQR 18 to 86 weeks) after enrolment. Follow-up data collection is ongoing.

Out of 462 runners who completed an online registration form, 268 runners enrolled, of which 135 had a history of knee surgery (46% females) and 133 were non-surgical controls (50% females). 60% of the surgery group had undergone anterior cruciate ligament reconstruction, 33% meniscus and/or cartilage surgery, and 7% other knee surgery. 54 participants previously enrolled were unable to continue in the study before attending baseline data collection. Of the 214 runners who remained in the study and attended baseline data collection, 108 had a history of knee surgery (49% females) and 106 did not have a history of knee surgery (51% females).

Participants will be followed for 10 years through ongoing patient-reported outcomes and continuous monitoring of training loads using wearable devices. At baseline, 4- and 10-year follow-up, knee MRI and knee-health patient-reported outcomes will be collected to evaluate structural and symptomatic knee osteoarthritis progression. Data will inform guidelines for safe running practices and rehabilitation post-knee surgery.