Kukkoaho placed fourth in men's 400 metres at the 1971 and 1974 European Championships and sixth at the 1972 Summer Olympics, where he set the still-standing Finnish national record of 45.49 seconds.

He won bronze at the 1974 European Championships in the 4 × 400 metres relay as part of the Finnish team.

[4] Kukkoaho won the national 400 m title again in 1972 (46.9) and was selected for the 1972 Summer Olympic Games in Munich, again for both the individual 400 m and the 4 × 400 m relay.

[7] In the relay the Finnish team of Stig Lönnqvist, Ari Salin, Ossi Karttunen and Kukkoaho ran 3:01.12, likewise placing sixth;[6][7] that time also still remains the national record.

[5] The Finnish team of Lönnqvist, Karttunen, Markku Taskinen and Kukkoaho ran 3:03.57 and placed a close third behind Great Britain and West Germany;[5] Finland was briefly disqualified due to Kukkoaho shoving France's anchor Francis Demarthon, but after a successful Finnish protest the disqualification was overturned and the team regained its medals.