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Ultra endurance events are defined as sporting activities lasting >6 hours and include events such as ultramarathon foot races, ultra triathlons, ultra distance swimming, ultra cycling, and cross-country skiing. Popularity in these events has risen especially over the last 25 years with increasing participation notably in ultramarathon races where an exponential increase in participation has been observed. This is in large part due to the increasing popularity and participation of women and master athletes in these events. Other endurance sports have seen similar increases but overall numbers are much lower compared with ultramarathon events.
Volker Scheer (Sat,) studied this question.