Custom foot orthoses improve performance, but do not modify the biomechanical manifestation of fatigue, during repeated treadmill sprints

Abstract

Purpose We determined the effect of custom foot orthotics manufactured from ethyl-vinyl acetate (EVA) and expanded thermoplastic polyurethane (TPU) materials, both compared to a control condition (CON; shoes only) during repeated sprints on running mechanical alterations. Methods Eighteen males performed eight, 5-s sprints with 25-s recovery on an instrumented sprint treadmill in three footwear conditions (EVA, TPU and CON). Mechanical data consisted of continuous (step-by-step) measurement of running kinetics and kinematics, which were averaged for each sprint for further analysis. Results Distance ran in 5 s decreased from first to last sprint (P < 0.001), yet with higher sprints 1-8 values for both EVA (P = 0.004) and TPU (P = 0.018) versus CON. Regardless of footwear condition, mean horizontal forces, step frequency, vertical and leg stiffness decreased from sprint 1 to sprint 8 (all P < 0.001). Duration of the propulsive phase was globally shorter for both EVA (P = 0.002) and TPU (P = 0.021) versus CON, while braking phase duration was similar (P = 0.919). In the horizontal direction, peak propulsive (P < 0.001), but not braking (P = 0.172), forces also decreased from sprint 1 to sprint 8, independently of conditions. Conclusion Compared to shoe only, wearing EVA or TPU custom foot orthotics improved repeated treadmill sprint ability, yet provided similar fatigue-induced changes in mechanical outcomes. Keyword Insoles • Instrumented treadmill • Running kinematics • Leg-spring behaviour Abbreviations ANOVA Repeated-measures analysis of variance CFO Custom foot orthotics CON Control condition EVA Ethyl-vinyl acetate GRF Ground reaction forces RPE Ratings of perceived exertion RSE Repeated sprint exercise TPU Thermoplastic polyurethane

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

“…Although CFOs slightly modified SA scores in some individuals tested in our study, the evidence regarding the effects of inserts on asymmetry is not strong regarding who may benefit and in which way. Previously, we did not observe any significant difference in the time course and magnitude of mechanical adjustments in response to repeated treadmill sprints when comparing shoe only to EVA or TPU inserts [19,20]. Reportedly, healthy individuals walking on a treadmill showed altered frontal and transverse plane foot kinematics with increasing stiffness of CFOs, leading to a reduction in rearfoot eversion and an increase in rearfoot abduction [30].…”

“…This study was part of a larger project investigating the effects of CFOs on stride mechanics during repeated treadmill sprints, but the primary outcome measures reported here (SA scores) are distinct from previous analyses [19,20]. This study used a counterbalanced randomized crossover design.…”

“…The sprints were conducted on an instrumented motorized treadmill (ADAL3D-WR, Medical Development-HEF Tecmachine, France), as described elsewhere [19,20]. The treadmill was mounted on a highly rigid metal frame, set at 0 • incline, fixed to the ground through four piezoelectric force transducers (KI 9077b; Kistler, Winterthur, Switzerland) and installed on a specially engineered concrete slab to ensure maximal rigidity of the supporting ground.…”

Acute intense fatigue does not modify the effect of EVA and TPU custom foot orthoses on running mechanics, running economy and perceived comfort

“…After a 10 min warm-up at 10 km/h, followed by a 3 min break used to put on the mask to collect expired gases, participants ran for 6 min at the speed associated with their first ventilatory threshold (13.8 ± 1.1 km/h) whereby running mechanics, RE and perceived comfort were evaluated. Participants were then allowed 5 min to rest in a standing position prior to undertaking a fatiguing task that consisted of performing eight, 5 s sprints separated by 25 s of rest (Girard et al 2020 ). Lastly, 2 min after the termination of the fatiguing task, participants repeated the 6 min run trial.…”

“…Tolerance to ground impact is often compromised as fatigue appears, which in turn may limit performance and/or increase injury risk, notably by increasing the magnitude and rate of loading (Li et al 2020 ). To date, little attention has been paid to the effectiveness of CFOs at reducing impact loading in situations of intense fatigue (i.e., repeated ‘all out’ efforts; Girard et al 2020 ), with participants typically tested in ‘fresh’ conditions only. Reportedly, CFOs reduced plantar loading under the hallux, medial midfoot, and lateral midfoot compared to prefabricated insoles by ~ 30–35% post-fatigue (12 min at treadmill speed of ~ 14.4 km/h) (Lucas-Ceuvas et al 2014).…”