There are few physiological reports on skyrunning （SR）, a mountain running event. This study aimed to examine the physical fitness characteristics of skyrunners based on the results of a maximal exercise test on level ground and an SR time attack in the field of Mt. Fuji.Eight healthy male subjects who participated in trail running and SR competitions performed the maximal exercise test at 0 m altitude. In addition, they performed the SR Time Attack as an Mt. Fuji field test and calculated LT and OBLA by blood lactate concentration. In the SR Time Attack, blood samples were taken before and after SR, and distance, time, and heart rate during SR were measured with a portable HR monitoring device with a GPS function. Study results showed that subjects were divided into two groups according to their performance in the SR Time Attack, with the upper group compared to the lower group. The upper group had a lower body fat percentage（≈5.0%） and intensity during SR equivalent to 80% VO2max; the WBI before SR was about 1.1, which did not change after SR, but was lower in the low group. In addition, thigh flexor strength was significantly lower in the lower group after SR; the ROS generated during the time attack of SR was within the acceptable range of biological defense mechanisms.
https://ror.org/01692sz90 
