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Background: The purpose of this study was to analyze running biomechanical alterations according to different slopes (flat, uphill and downhill) and distance, during a 40-km mountain trail running race., Methods: Throughout the race, eight runners were equipped with Runscribe ® inertial units placed on each running shoe. Measurements included spatiotemporal parameters (contact time, step frequency, stride length, running speed), kinetic (impact peak and braking force) and kinematic data (foot pronation velocity and foot pronation excursion). For data analysis, the race was divided in two halves, from which three types of matching segments were extracted: two uphill sections (U1, U2), two downhill sections (D1, D2) and two flat sections (F1, F2)., Results: Intra-section comparisons revealed that during the second part of the race, running speed decreased in all sections. In uphill sections, stride length increased, step frequency and contact time variability decreased. On flat and downhill sections, contact time increased whereas step frequency and stride length decreased. Step frequency and contact time variability increased for both uphill and downhill sections. With regards to downhill sections only, impact peak, horizontal braking force and foot pronation velocity decreased. Foot strike pattern switched from a rearfoot to a midfoot-strike pattern. Contact time, horizontal breaking force pronation velocity and foot strike pattern variability increased., Conclusions: Over a 40-km mountain trail running race, changes in running biomechanics are important data which should be taken into account by runners and coaches for training preparation, race strategy as well as for injury prevention.

Background: The aim of this study was to evaluate the effect of 12 weeks of use of orthopedic insoles equipped with a metatarsal retro-capital bar (MRCB) on plantar pressure under the feet and lower limb kinematic variables during running., Methods: Two groups of 10 runners used for 12 weeks while running orthopedic insoles without correction or equipped with a MRCB. All participants performed successively a standing posture (CoP displacement) test and a running test at 11 km.h-1 (lower limb kinematic variables) using with flat insoles and orthopedic neutral or MRCB insoles at the beginning (T0), after 4 (T4) and 12 weeks (T12) of use., Results: For the MRCB group, CoP moved backwards while forefoot plantar pressure was decreased during standing position at T4 and T12 compared to T0. During running, the plantar pressure under the 2nd, 3rd and 4th metatarsal heads was reduced with MRCB at T0, T4 and T12. The one under the 1st metatarsal head was decreased at T4 and T12, when MRCB or flat insoles were used. The maximal extension and the total amplitude of ankle were slightly increased at T4 and T12 with or without wearing MRCB insoles. Similar changes in knee joint kinematics were observed but only at T12. Any significant changes were found in runners that used orthopedic insoles without correction., Conclusions: Orthopedic insoles equipped with MRCB involve lower plantar pressure under the metatarsal heads, which may be of interest to treat forefoot injuries in runners.