Lower-Limb Connective Tissue Morphologic Characteristics in Runners. How Do They Relate with Running Biomechanics and Tendon Pathology? A Systematic Review

Abstract

Although the role of connective tissue in running injuries and biomechanics has been widely investigated, systematic reviews on this issue were rarely reported. The aim of this study is to systematically review the current literature regarding the morphological characteristics (i.e., cross-sectional area and thickness) of the main connective tissue of the lower limb in runners and its relationship with running biome-chanics and tendon pathology. The main keywords used were: Achilles and patellar tendons, plantar fascia, ultra-sound, thickness, cross-sectional area and running. Observational design English-writ-ten studies published between January 2000 and September 2020 were included. After exclusion criteria were applied, 34 studies remained. 16 studies analysed connective tissue related to sample characteristics where mainly the differences between runners and controls were studied along other factors such as gender, weight and nationality. Regarding running biomechanics, 10 studies assessed connective tissue on running biomechanics with focusing on foot strike pattern and footwear characteris-tics. Regarding tendon pathology, 8 studies analysed the connective tissue assessing, mainly, whether the pathological tendons are thicker. Runners show higher tendons, in terms of thickness and CSA, than control subjects and athletes from other disciplines whose tendons are subjected to lighter loads. Adaptation to load leads to better performance, what seems to explain these morphological differences. Study registration. None.