Career
Janistyn made his official debut at the 2008 Summer Olympics in Beijing, where he competed in two freestyle events. He swam on the second leg of the men"s 4 × 200 m freestyle relay, posting his split time of 1:50.48. Janistyn and his teammates Dominik Koll, Markus Rogan, and David Brandl finished heat two in fifth place and ninth overall, for a total time of 7:11.45.
Janistyn, however, failed to advance into the final, as he placed twenty-first out of 37 swimmers in the evening"s preliminaries.
Four years after competing in his first Olympics, Janistyn qualified only for the men"s 4 × 200 m freestyle relay at the 2012 Summer Olympics in London. Swimming the anchor leg, Janistyn recorded a time of 1:51.37, and the Austrian team (composed of Rogan, Brandl, and Christian Scherübl) went on to finish heat two again in eighth place and sixteenth overall, for a total time of 7:17.94.