He won the Elfstedentocht, the world's largest speed skating competition twice.

[1] Adema won the seventh Elfstedentocht by himself on 6 February 1941 in a time of 9 hours 19 minutes, a race record.

[3] * Women were first allowed to take part in the tour proper in 1985; before then they had to skate with the amateurs and no award was given.

** After shared wins in 1933 and 1940, when the front-runners decided not to compete but join hands to cross the line together, this practice was forbidden by the organisation.

Jan van der Hoorn, Aad de Koning, Jeen Nauta, Maus Wijnhout and Anton Verhoeven however ignored this rule when they crossed the finish line in unison.