ECSS Paris 2023: OP-BM25
INTRODUCTION: Running in advanced footwear technology (AFT) has repeatedly been demonstrated to improve running economy (RE) on average compared to traditional running shoes [1, 2]. The range in individual improvements, however, is broad, with some studies even showing no or negative effects [3]. A recent framework [4] proposes that besides the purely mechanical advantages of AFT materials, the biomechanical interplay between athlete and shoe determines part of the shoes' effectiveness. Yet, no study has investigated individual running biomechanics across various AFT models in relation to changes in RE. Therefore, this study aimed to identify biomechanical factors associated with intra-individual changes in RE when running in various AFT models using a within-subject design. METHODS: Twenty-two competitive distance runners (11 female, age: 33.1±6.2 years, BMI: 21.0±1.7 kg/m2) completed three 5-minute running bouts at their individual marathon pace (10.9–19.5 km/h) on an instrumented motorized treadmill in randomized order. They wore three standardized AFT models (Asics Metaspeed Sky+, Nike Alphafly Next% 2, Puma Fast-R Nitro Elite v1). Respiratory gas exchange was measured continuously, and RE was defined as the energetic cost of transport (eCoT) [5]. Three-dimensional kinematics and spatiotemporal variables were acquired using a 12-camera motion capture system and an embedded pressure plate. Akaike Information Criterion-based model averaging, and least absolute shrinkage and selection operator (LASSO) were used with linear mixed-effects models to identify biomechanical parameters associated with intra-individual changes in RE across AFT models. RESULTS: Both model selection strategies identified ground contact time (GCT) as the only robust predictor of intra-individual RE changes. In the final model, shorter GCT was significantly associated with lower eCoT (β=0.025, 95% CI [0.010, 0.040], p=0.002), reflecting approximately 1% improvement in RE per 4 ms decrease in GCT. Step rate and peak metatarsophalangeal joint flexion showed high relative model importance (sum of Akaike weights) but were not statistically significant (both p>0.05). No group-level differences in eCoT were found between AFT models (p=0.246). CONCLUSION: Reduced GCT was the only significant biomechanical predictor of improved RE across three AFT models. The absence of group-level RE differences highlights substantial inter-individual variability, suggesting that none of the AFT models used here were universally optimal. These findings may inform individualized footwear selection for competition. Future research should further investigate the interaction of AFT properties and individual biomechanics to advance our understanding of the individual responses to AFT. 1. Hoogkamer W et al. Sports Med 2018;48:1009–1019. 2. Hunter I et al. J Sports Sci 2019;37:2367–2373. 3. Knopp M et al. Sports Med 2023;53:1255–1271. 4. Connick MJ, Lichtwark GA. J Appl Biomech 2025;41:1–7. 5. Péronnet F, Massicotte D. Can J Sport Sci 1991;16:23–29.
Read CV Dominik FohrmannECSS Paris 2023: OP-BM25
INTRODUCTION: In order to run, individuals with lower-limb amputation need running-specific prostheses (RSP) designed to replicate the lower-limb mass–spring system [1]. Prosthesis stiffness is a key parameter [2,3] and is commonly selected solely based on body mass. However, this approach may be reductive, as optimal stiffness likely depends on individual running mechanics and slope conditions. This study aimed to investigate the influence of blade stiffness on running pattern and energy cost of running (Cr). METHODS: Sixteen unilateral transtibial amputee runners (13 males; 42.6 ± 11.7 y; 177.6 ± 9.1 cm; 71.7 ± 10.5 kg), habitual RSP users, completed 4-min treadmill trials at self-selected speed under three blade stiffness conditions: habitual (HAB), +1 (HARD), and −1 (SOFT) categories on level, uphill (+10%), and downhill (−10%) slopes. Comfort was assessed with a visual analog scale, and Cr was calculated from breath-by-breath V̇O₂ during the last minute. Spatiotemporal parameters and vertical and anteroposterior forces were measured on an instrumented treadmill. Kinematics for both limbs were recorded with 34 reflective markers, allowing prosthesis modelling and quantification of elastic energy storage and release angle. Linear mixed models assessed the effects of blade stiffness on all variables and the relationship between Cr and elastic energy release. RESULTS: No significant effect of blade stiffness on Cr was observed, although comfort was higher with the HAB blade compared to the HARD blade (p<0.05). In level running, only 29% of participants exhibited lower Cr with HAB, whereas this proportion increased to 62.5% during uphill running. A negative relationship (p<0.05) was found between Cr and elastic energy release, whereas no relationship was found between Cr and comfort. Blade stiffness had no effect on biomechanical parameters, except for a longer cycle time of the intact limb with the SOFT blade compared to HAB and HARD during uphill running (p<0.001). Regardless of blade stiffness, the intact limb showed greater vertical oscillation (p<0.05) and higher vertical peak and braking forces (p < 0.001), whereas propulsion force was higher for the amputee limb (p<0.001). Biomechanical asymmetry between limbs was influenced by slope (p<0.05). CONCLUSION: Although no effect of blade stiffness on energy cost was observed, substantial inter-individual variability suggests participant-specific responses that cannot be predicted from comfort perception. For many participants, the HAB blade was not the most economical, and slope affected the most efficient blade. Cr partly depends on elastic energy release, while stiffness has small effect on biomechanics running pattern or interlimb asymmetries. These findings indicate that body mass alone is insufficient to guide blade stiffness selection and the choice may differ between road and trail (graded) running. REFERENCES 1. Nolan et al., Foot and Ankle Surgery, 2008 2. Beck et al., J Appl Physiol, 2017 3. Barnett et al., Gait & Posture, 2022
Read CV Robin MacchiECSS Paris 2023: OP-BM25
INTRODUCTION: The quest for sub-2h marathons established curved plates and resilient foams as the hallmark of advanced footwear technology. Although longitudinal bending stiffness (LBS) is a core feature, its impact on running economy (RE) remains equivocal, suggesting a U-shaped relationship where excessive stiffness may negate metabolic savings.This study investigates the biomechanical parameters of transitioning from a stiff threshold to a stiffest configuration. This study quantifies the influence of these two LBS gradients on RE and lower-limb kinetics in elite rearfoot strikers across different speeds. We aim to clarify the mechanical trade-offs between metatarsophalangeal (MTP) efficiency and ankle stability in ultra-stiff footwear. METHODS: Nine male rearfoot strikers were recruited. This study evaluated two experimental condition shoe models with different LBS increments(Stiff :Adizero Adios Pro 4, 21.0 N·mm -1 and Stiffest: PLAID 3.0, 28.8 N·mm -1 . RE (Cosmed K4b2) was measured at 16 km/h; biomechanics (Qualisys 200Hz; Kistler 1000Hz) were captured at 12, 14, 16 km/h (±5%). Paired t-tests were used (p < 0.05). RESULTS: (1)RE: No significant differences were observed in RE, including VO2/kg, respiratory quotient, and energy expenditure, at 16 km/h (p > 0.05). (2)Spatiotemporal: At 16 km/h, flight time was significantly shorter in PLAID 3.0 (p = 0.014). As speed decreased, this adaptation became more pronounced: at both 14 km/h and 12 km/h, PLAID 3.0 exhibited a significantly prolonged contact time (14 km/h: p = 0.012; 12 km/h: CONCLUSION: While RE was comparable at 16 km/h, the ultra-high LBS of PLAID 3.0 significantly optimized MTP efficiency by reducing energy dissipation and enhancing active energy return across all tested speeds. These findings support the lever effect of carbon plates, yet the observed increase in contact time and decrease in flight time suggest a transition toward a rolling gait strategy rather than a bouncing mechanism to accommodate extreme stiffness.Crucially, the elevated ankle eversion velocity and increased negative work indicate that supra-optimal LBS shifts mechanical demands proximally. This mechanical trade-off implies that while ultra-high stiffness footwear facilitates distal energy management, it simultaneously imposes greater stability requirements and eccentric loads on the ankle complex. Consequently, athletes with superior foot-core strength and ankle stability may be better positioned to exploit the propulsive advantages of high-stiffness AFT, whereas others may face an increased risk of fatigue-related compensatory injuries. These insights provide a scientific framework for individualized footwear selection and the structural optimization of future racing shoe designs.
Read CV Yanbing LiECSS Paris 2023: OP-BM25