Continuously monitoring runners' adaptive strategies to prolonged running on an outdoor track with straight and curved paths : insights from the varying intersegment coordination variability and shock absorption during a full marathon

Abstract

Objectives: This study investigated changes in lower limb intersegment coordination variability and impact shock in runners during a full marathon, whereas to assess how increasing mileage and track conditions (straight vs. curved paths) influenced these metrics in an outdoor environment. Design: A field-based observational study. Methods: Twenty-three amateur runners completed a self-paced marathon, during which inertial measurement units were used to collect segment kinematic data for computing coordination variabilities and impact shocks. Generalized estimating equations were employed to examine the effects of mileage (increments of 5 km) and track conditions (straight/curved) on the measures. Results: Runners exhibited increased coordination variabilities in sagittal planes and decreased coordination variabilities in non-sagittal planes as the race progressed. Significant changes were identified in coordination variabilities of shank vs. rearfoot at the later stages of the marathon (Wald χ2 = 4.33–7.40, p = 0.007–0.037). All coordination variabilities were consistently lower on curved paths compared to straight paths with significant differences noted in the coupling of pelvis vs. thigh (Wald χ2 = 24.25, p < 0.001). Tibial and pelvic impact shocks were elevated with increasing mileage after adjusting for running speed (Wald χ2 = 21.99–36.17, p < 0.005). Conclusions: The runners showed distinct modulation of coordination variability across movement planes during prolonged running. Specifically, coordination variabilities were contained in non-sagittal planes while greater fluctuations were allowed in sagittal planes. These changes may compromise the norm of lower limb load attenuation, although further studies are warranted to explore their generalizability and the underlying mechanism.