It was hypothesized that for each mountain running competition, there is a certain individual performance level below which running times increase dramatically. The running times of 869 finishers of 3 international mountain running competitions have been analysed. A hyperbolic association was demonstrated between finish times in mountain running competitions and individual performance at the anaerobic threshold (VO2AT(Race)). Due to the non-linear association, there is an increasing effect on both the finish time and the change of finish time with decreasing aerobic performance. In all three competitions, the change of finish time is about 7 times more pronounced in mountain runners with the lowest VO2ATL,, compared to those with the highest values of VO2AT(Race). Both athletes and organizers should keep in mind these effects of decreasing aerobic performance on running times and potentially associated risks.