Introduction Carbon plates have been used to increase running shoes` longitudinal bending stiffness (LBS), but their effect during a long duration run remains unknown. Our study aimed to identify the effect of LBS on energy cost of running (Cr), biomechanics, and fatigue during a half-marathon. Methods Thirteen well-trained male runners (half-marathon time <1 h 40) performed two half-marathons at 95% of the running speed associated with their second ventilatory threshold on two separate visits, with either high-LBS (HLBS) shoes, with carbon plates) or standard-LBS (SLBS) shoes. Before and after the half-marathon, Cr at 12 km·h-1 with both shoes (two 6-min bouts: Cr12) and ankle plantar flexor (PF) force were measured. During the half-marathon, running kinematics, shoe perceived comfort, and Cr were assessed. Results During Cr12 measurements before and after the half-marathon, HLBS was 1.0% ± 2.1% more economical than SLBS (P < 0.001). During the half-marathon, Cr increased with running duration (P = 0.048), but there was no distance×condition effect. HLBS increased contact time (+3%, P = 0.01), decreased metatarsophalangeal joint dorsiflexion (-9%, P = 0.01), and was perceived less comfortable than SLBS, independently from running duration. At the end of the half-marathon, HLBS shoes led to higher PF force loss (-20.0% ± 9.8% vs -13.3% ± 11.0%, P = 0.048). Conclusions Adding curved carbon plates in the running shoes slightly improved Cr during short running bouts at low intensity but not during a half-marathon. This discrepancy may be explained by day-to-day Cr variability and variation in shoe comfort. PF fatigue was higher with HLBS shoes, but the accentuated fatigue did not further impact the biomechanical perturbations induced by the plates. Our results suggest that carbon plates alone do not provide a significant advantage for half-marathon performance.
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