How do training experience and geographical origin of a runner affect running biomechanics?

Background: Several studies compared African runners with runners from other places with difference ethnicities to identify biomechanical factors that may contribute to their extraordinary running performance. However, most studies only assessed runners at the elite level. Whether the performance difference was a result of nature or nurture remains unclear. Research questions: This case study aimed to assess the effect of geographical origin and the effect of training on running biomechanics. Methods: We recruited twenty male runners from two regions (Asian and Africa) at two performance levels (elite and recreational), and asked them to run on an instrumented treadmill at 12 km∙h−1. We measured running kinetics and kinematics parameters, and focused on the parameters that have been shown associated with running performance. We used Friedman test to compare the effect of geographical origin and training on running biomechanics. Results: Compared to recreational runners, elite runners applied higher amount of ground reaction force in both vertical and anterior-posterior directions (P < 0.05, Cohen's d = 1.63–2.03), together with a longer aerial time (P = 0.039, Cohen's d = 1.11). On the other hand, African runners expressed higher vertical stiffness than Asian runners (P = 0.027, Cohen's d = 0.98). However, the increased vertical stiffness in African runners did not lead to a higher vertical loading rate (P > 0.555, Cohen's d < 0.3), which could be a result of a lower footstrike angle during landing (P = 0.012, Cohen's d = 1.36). Significance: For elite runners, the higher amount of ground reaction force might facilitate a longer aerial time, but could also lead to higher amount of mechanical energy loss. African runners expressed higher vertical stiffness and higher step rate, which might lead to a lower CoM vertical displacement, and furthermore reduce mechanical energy loss.