As a javelin thrower, he won gold and bronze medals at the International University Games and was national champion of Estonia and later the Soviet Union.

At the 1937 International University Games in Paris Issak won gold in the javelin with a throw of 70.25 m, a meeting record that was only broken twenty years later.

[1][3] Issak placed fifth at the 1938 European Championships, also in Paris, and recorded his personal best (72.07 m) in Tartu in July 1939.

[1] During World War II Issak served in the Red Army[1] and the destruction battalions.

[1] From 1958 to 1978 he worked for the culture magazine Kultuur ja Elu, eventually becoming its editor-in-chief.