No effect of custom foot orthoses and sex on mechanical asymmetries during treadmill running

Abstract

We investigated the influence of custom foot orthoses and sex on mechanical asymmetries during treadmill running. Eighteen injury-free trained individuals (9 females) ran on an instrumented treadmill for six minutes at a speed 10% below their first ventilatory threshold (average: 9.9±1.3 km/h) under four footwear conditions: original shoe liner (control), two custom orthotics (one EVA, one TPU), and a hybrid (EVA heel, TPU forefoot). Vertical and antero-posterior ground reaction forces were recorded after ~5 minutes of running, encompassing 40 steps. Mechanical asymmetry was assessed using the ‘symmetry angle’ (SA) score. There were no significant main effects for condition (all P≥0.302) or sex (P≥0.137), and no significant condition × sex interactions for any variables (P≥0.063). Mean SA scores were less than 2% for contact time (0.39±0.23%), flight time (1.90±1.35%), step frequency (0.34±0.26%), peak vertical force (1.44±1.15%), and mean vertical loading rate (1.79±1.17%). Vertical and leg stiffness had mean SA scores of 3.11±1.73% and 1.86±1.00%, respectively. For braking (1.56±0.78%) and push-off (1.54±0.81%) phases and peak braking (2.94±1.61%) and push-off (2.33±1.17%) forces, mean SA scores ranged from ~1.5% to 3.0%. Overall, both male and female runners showed relatively even strides, and custom foot orthoses did not significantly alter natural stride asymmetries.