Japan Championships in Athletics
Isozaki established herself as the nation's top sprinter at a very early age. She won a 100 m/200 m double at the Japan Championships in Athletics in 1981 at age sixteen. The following year she won the 200 m national title in a championship record of 24.18 seconds. This improved the Japanese national record of Kaihara Sumiko (24.27). She later improved to 24 seconds flat and this would last as the record until 1992, when Kazue Kakinuma became the first Japanese woman under 24 seconds for the event.