Meaning 1:

ultra-athlete - a person who competes in and trains for ultra-triathlons long-distance triathlons: "The term generally refers to all triathlon events of distance greater than the Ironman Triathlon. Thus, every ultra triathlon event must involve more than 2.4 miles (3.86 km) of swimming, 112 miles (180.25 km) of cycling, and a full marathon (26.2 mi or 42.2 km) of running.... swimming, cycling and running may take place on consecutive days" (Source: Wikipedia)