Running kinematics, spatiotemporal variation and lower limb strength at different stages of a 156-km ultra-trail race

BACKGROUND: Ultra-trail running is increasingly popular, yet most research on biomechanics focuses on road running or treadmills. This study assesses changes in foot strike pattern (FSP), step frequency, and other biomechanical parameters over a 156-km ultra-trail race. METHODS: Fifty-five experienced runners participated in the Trail Scientifique de Clécy, a 156-km race with 6000 meters of elevation gain. Biomechanical data were collected at the end of each 26-km lap using video for FSP and Optojump for other parameters. Muscle strength was measured via maximal voluntary isometric contraction (MVIC) of the hip abductors and ankle plantar flexors. RESULTS: Forty-one runners completed the race. FSP remained consistent. Step frequency decreased initially (P=0.003) before stabilizing. Self-selected speed declined by 14.2% (P