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<0.001), and step length reduced by 12.6% (P<0.001). Ground contact time increased (+12.9%, P<0.001), while flight time remained stable. Leg stiffness showed a non-significant decreasing trend (P=0.048). MVIC for hip abductors and ankle plantar flexors slightly decreased late in the race (P=0.015 and P=0.004).

CONCLUSIONS

Experienced ultra-trail runners maintain consistent FSP while strategically adapting other biomechanical parameters to manage fatigue, supporting sustained performance and injury prevention in ultra-endurance races.