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

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.

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.

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.