No Effect of EVA and TPU Custom Foot Orthoses on Mechanical Asymmetries during Acute Intense Fatigue

Abstract

This study examined the impact of custom foot orthoses made of ethyl-vinyl acetate (EVA) and expanded thermoplastic polyurethane (TPU) materials, both compared to a control condition (CON; shoes only), on mechanical asymmetries during repeated treadmill sprints. Eighteen well-trained male runners executed eight, 5-s sprints (rest: 25 s) on an instrumented motorized treadmill in three footwear conditions (EVA, TPU, and CON). We evaluated the group mean asymmetry scores using the ‘symmetry angle’ (SA) formula, which assigns a score of 0% for perfect symmetry and a score of 100% for perfect asymmetry. There was no condition (all p ≥ 0.053) or time (p ≥ 0.074) main effects, nor were there any significant time × condition interactions on SA scores for any variables (p ≥ 0.640). Mean vertical, horizontal, and total forces presented mean SA values (pooled values for the three conditions) of 2.6 ± 1.9%, 2.9 ± 1.6%, and 2.4 ± 1.8%, respectively. Mean SA scores were ~1–3% for contact time (1.5 ± 0.5%), flight time (3.0 ± 0.3%), step frequency (1.1 ± 0.5%), step length (1.9 ± 0.7%), vertical stiffness (2.1 ± 0.9%), and leg stiffness (2.4 ± 1.1%). Mean SA scores were ~2–6.5% for duration of braking (4.1 ± 1.6%) and propulsive (2.4 ± 1.0%) phases, and peak braking (6.2 ± 2.9%) and propulsive (2.1 ± 1.4%) forces. In well-trained runners facing intense fatigue, wearing custom foot orthoses did not modify the observed low-to-moderate natural stride mechanical asymmetries.

Mechanical asymmetries remain low-to-moderate during 30 min of self-paced treadmill running

“…Contrary to our hypothesis, adjustments occurring during the braking and push-off phases exhibited comparable SA scores. This finding is consistent with previous observations during repeated-running sprints ( Van Alsenoy et al, 2023 ) and perceptually-regulated interval running ( Girard et al, 2021 ). This indicates that alterations in foot strike pattern throughout the run were not significantly amplified on either the weaker or strong leg by braking more in the early stance phase and pushing less forcefully forward.…”

“…The mean SA scores for time-based gait parameters (e.g., contact and flight times, step frequency and duty factor, braking and push-off phase durations) during the run consistently remained low, generally below 1.5%. This pattern aligns with findings from other studies ( Girard et al, 2023 ; Van Alsenoy et al, 2023 ), suggesting that, within this athletic cohort and under the current conditions, spatio-temporal gait variables exhibit a high degree of symmetry and remain stable over a 30-min run. Contrastingly, the highest SA scores were observed for vertical stiffness, slightly exceeding 5%.…”

“…Regardless, the range of SA scores for most runners was contained within approximately twice the magnitude of the mean value, irrespective of the time interval. This pattern mirrors observations made during treadmill graded exercise test ( Girard et al, 2022 ) and at submaximal constant-velocity ( Hanley and Tucker, 2018 ) or repeated sprints ( Van Alsenoy et al, 2023 ). For instance, Hanley and Tucker (2018) found substantial inter-individual differences on an individual level, especially for spatiotemporal parameters, during a 10,000 m treadmill run at constant velocity.…”

“…Secondly, our study did not control for the use of specific foam (carbon plate) shoes or foot orthoses by runners who may have worn them for comfort or to mitigate gait alterations while wearing their habitual footwear. However, it is important to mention that Van Alsenoy et al (2023) found that wearing custom foot orthoses did not significantly alter the observed low-to-moderate natural stride mechanical asymmetries in well-trained runners experiencing intense fatigue. Thirdly, we did not assess laterality or leg preference in our study, which could have provided insights into whether limb dominance influenced mechanical side-to-side differences during treadmill runs ( Brown et al, 2014 ).…”

“…In recent years, there has been a growing interest in examining changes in mechanical asymmetry in fatigued runners due to its perceived impact on performance and injury ( Heil et al, 2020 ). Researchers have focussed extensively on alterations in lower limb asymmetry during both maximal ( Girard et al, 2017 ; Girard et al, 2023 ; Van Alsenoy et al, 2023 ) and constant submaximal intensity running ( Brown et al, 2014 ; Hanley and Tucker, 2018 ; Gao et al, 2020 ; Melo et al, 2020 ; Gao et al, 2022 ), yielding conflicting findings ( Heil et al, 2020 ). For instance, elite female athletes performing eight 5-s repeated treadmill sprints showed no significant differences in most stride mechanical variables ( Girard et al, 2023 ).…”