抄録
Ultra-trail running （UTR） involves prolonged running and walking over mountainous terrain with elevation gain and unstable surfaces.These demands impose repetitive eccentric loading on the knee extensors and challenge the ability to maintain weight-bearing force. This three-year longitudinal case report investigated changes in Weight-Bearing Index（WBI） and knee flexor strength in a middle-aged male trail runner who repeatedly participated in UTR and ultramarathon（UM） events between 2023 and 2025. Muscle strength was measured before each race, within 48 hours post-race, and during early recovery. Across races, WBI showed a greater post-race decline than knee flexor strength（ maximum -58.3% vs. -22.7%）, indicating selective fatigue of the knee extensors. Severe weather and muddy trails in UTR events amplified weight-bearing demands and exacerbated WBI reduction. Running speeds at lactate threshold （LT） and OBLA remained within a relatively narrow range over the three years （VLT 6.0–8.5 km/h, VOBLA 8.5–10.5 km/h）, with a transient reduction before the 2025 UM and partial recovery before the 2025 UTR, suggesting that submaximal metabolic endurance was preserved despite a decrease in maximal oxygen uptake. These findings indicate that elevation-focused training and technique modifications that mitigate excessive extensor loading may be
important for the safe completion of UTR events.
https://ror.org/01692sz90 
