Official Publication of the National Center for Trauma Research Trauma Monthly 2251-7464 31 1 2026 01 01 Long-term Effect of Training on Different Surfaces on Knee Muscular Co-Contraction During Running in Individuals with Over-Pronated Feet 1686 1700 244303 10.30491/tm.2025.545695.1876 EN AmirAli Jafarnezhadgero Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran 0000-0002-2739-4340 Fariborz Imani Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran 0009-0002-5765-1771 Raha Noroozi Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran Hamed Sheikhalizadeh Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran 0000-0002-5788-4447 Journal Article 2025 09 07 <strong>Introduction: </strong>Over-pronated feet (OPF) are associated with altered lower-limb mechanics and elevated injury risk during running. Long-term training on different sport surfaces may modulate neuromuscular control, including knee muscular co-contraction; however, surface-specific adaptations in individuals with OPF remain insufficiently characterized<span dir="RTL" lang="FA">.</span> To determine the long-term effects of training on natural grass, artificial turf, and synthetic surfaces on knee muscular co-contraction during running in individuals with OPF.<br><strong>Method</strong>: In this randomized controlled trial (IRCT20170806035517N5), thirty-two adults (aged 18–30 years) with clinically diagnosed OPF were randomly allocated to one of three intervention groups (natural grass, artificial turf, or synthetic surface) or a no-training control group. The intervention groups completed a supervised, eight-week running program with standardized frequency and progression. Surface electromyography (sEMG) was used to quantify knee muscular co-contraction during treadmill running at a controlled speed. General co-contraction and directed flexor-extensor co-contraction indices were computed over discrete stance sub-phases (heel-contact, mid-stance, and push-off) using established processing pipelines. Assessments were performed pre- and post-intervention by the same blinded operators. Group-by-time effects were examined for primary outcomes, with alpha set at 0.05.<br><strong>Result: </strong>No significant changes emerged for general knee co-contraction across time or between groups. In contrast, significant group-by-time interactions were observed for directed flexor-extensor co-contraction during mid-stance (p = 0.035) and push-off (p = 0.020), indicating that training induced surface-specific neuromuscular adaptations rather than uniform joint stiffening. A main effect of time was also noted at heel-contact (p = 0.050), consistent with a generalized training-related modulation early in the stance phase. Collectively, these patterns suggest that extended exposure to distinct surfaces selectively re-tunes knee muscle coordination strategies in individuals with OPF without globally increasing co-contraction.<br><strong>Conclusion<span dir="RTL" lang="FA">: </span></strong> Eight weeks of running training on different surfaces prompted targeted adjustments in knee flexor-extensor coordination in runners with OPF, while general co-contraction remained unchanged. Although such adaptations may be beneficial for control, they might not fully mitigate injury risk in this at-risk population. Individualized surface selection alongside integrative neuromuscular conditioning should be considered in rehabilitation and return-to-running planning for individuals with OPF. https://www.traumamon.com/article_244303_df20af20b58cf9ddf6add2833c94d977.pdf