Abstract
PurposeWe 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.MethodsEighteen 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.ResultsDistance 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.ConclusionCompared to shoe only, wearing EVA or TPU custom foot orthotics improved repeated treadmill sprint ability, yet provided similar fatigue-induced changes in mechanical outcomes.
Highlights
The capacity to reiterate “all out” efforts with incomplete recoveries depends, on metabolic and neuro-mechanical factors (Girard et al 2011a)
Participants performed, at the same time of day (±1 h) and 4–5 days apart, eight 5-s treadmill sprints with 25-s recovery in different footwear conditions: a control session where participants ran with standardised footwear, custom foot orthotics (CFOs) made of ethyl-vinyl acetate (EVA) and thermoplastic polyurethane (TPU)
Our main finding was that CFOs improve performance during repeated treadmill sprints, yet with similar positive effects (e.g. ~+ 4% on averaged sprints 1–8 distance covered) for EVA and TPU materials
Summary
The capacity to reiterate “all out” efforts with incomplete recoveries (i.e. repeated sprint ability) depends, , on metabolic and neuro-mechanical factors (Girard et al 2011a). Identifying the onset of fatigue through ground reaction forces (GRF) monitoring during repeated sprint exercise (RSE) may be helpful in providing early warnings of increased injury risk in many team sports. An important limitation of existing RSE literature is the lack of continuous measurements of running velocity and GRF including horizontal force production (Girard et al 2011b, c). Along with the expected progressive slowing of running velocity, these authors observed both a significant decrease in the capability to produce total (resultant) GRF and a significant and even larger decrease in the ability to apply it with a forward orientation during acceleration. Wearing foot orthoses altered neuromuscular control during a sub-maximal, 1-h constant-velocity treadmill run and partly protected from the resulting fatigue-induced reductions in rapid force development characteristics of the plantar flexors (Kelly et al 2011). Identification of the biomechanical manifestation of fatigue during RSE with versus without CFOs is currently lacking
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