The oxygen cost (CM) of running during the cycle-run transition of a triathlon has previously been studied for senior triathletes, but never in young triathletes. This study evaluates the effect of cycling on the evolution of the CM, in elite young triathletes, during a cycle to run transition in triathlon. Six subjects carried out two tests in random order: 1) Transition (T), consisted of a 30 min cycle at 3.5 W\u00b7kg-1 followed by a 3000m run at maximum speed in a 400 m track (7.5 laps). 2) Control run (C), consisted of a 3000 m run at maximum speed. No differences (p<\/em><0.05) were found between C and T for the CM (250.46\u2009\u00b1\u200921.47 vs. 256.22\u2009\u00b1\u200917.82\u00a0mL O2\u00b7kg-1\u00b7km-1, respectively), neither in the oxygen uptake (VO2) (4238\u2009\u00b1\u2009451 vs. 4220\u2009\u00b1\u2009604 mL\u00b7min-1, respectively). On the other hand, the score was significaly higher (p<\/em><0.05) in T (669,2\u2009\u00b1\u200923,8 vs. 646,0\u2009\u00b1\u200915,8 s, respectively). Only in the first lap of each 3000 m trial significant differences (p<\/em><0,05) were found for the studied variables, as expected because of the previous fatigue produced in T trial. In conclusion, our young elite triathletes did not experience alteration in CM of running during the cycle-run transition of a triathlon.<\/p>\n\n