Fatigue effects on angular kinematics in male recreational runners grouped by functional response.

Background: While current evidence on injury risk factors remains limited, this study aims to provide insights into how fatigue-induced changes in biomechanical risk factors (BRF) differ between runners, potentially offering a new approach to understanding the development of running-related injuries. Thirty-nine (N = 39) male recreational runners underwent analysis of lower leg angular kinematics, heart rate, blood lactate levels, and perceived effort before and after a 30-minute exhaustive continuous treadmill running test.

Results: Three functional groups (FG) were identified using the K-means algorithm, which grouped participants based on changes in lower limb angular kinematics between pre- and post-fatigue. While FG1 and FG2 exhibited similar behaviours to maintain their usual running dynamics (e.g. no significant changes in hip flexion at touchdown and toe-off, and similar reductions in leg stiffness after fatigue), FG3 showed more pronounced changes, including increased hip flexion (7.4%) and knee flexion (21%) at touch-down, as well as increased knee flexion at maximal knee flexion (6%) and at the toe-off instant (9%) during the running cycle.

Conclusions: Fatigue-induced alterations in the considered biomechanical risk factors allow for the functional grouping of recreational athletes. Changes in FG3 impact running patterns and alter running economy-related variables, which may be associated with an increased injury risk and could guide future research into tailored training and preventive strategies.