No effect of custom foot orthoses manufactured from EVA and/or TPU materials and sex on mechanical asymmetries during treadmill running in trained runners.

We investigated the influence of custom foot orthoses and sex on mechanical asymmetries during treadmill running. Eighteen trained, injury-free individuals (9 females) ran six minutes at 10% below their first ventilatory threshold (average speed: 9.9 ± 1.3 km/h) on an instrumented treadmill under four footwear conditions: original shoe liner (control), two custom orthotics [EVA and TPU], and a hybrid (EVA heel, TPU forefoot). Vertical and antero-posterior ground reaction forces were recorded after ~5 minutes, encompassing 40 steps. Mechanical asymmetry was assessed using the 'symmetry angle' (SA) score. No significant main effects were found for condition (all P ≥ 0.302), sex (P ≥ 0.137), or condition × sex interactions (P ≥ 0.063). Mean SA scores were <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 SA scores of 3.11 ± 1.73% and 1.86 ± 1.00%. 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, SA scores ranged from ~1.5-3.0%. Both sexes exhibited even strides, with orthoses not affecting natural asymmetries. Orthoses of similar shape but different materials are unlikely to alter gait symmetry, suggesting unilateral assessments may suffice and reduce testing demands.