While there she was a keen volleyball player and her speed led the coach to suggest she try sprinting with the school track and field team.

[3] She was picked for the Japanese women's team at the 1982 Asian Games in New Delhi and the seventeen-year-old Isozaki was one of the star performers of the tournament.

[4] She was the first woman to complete a 200 m/400 m double at the Asian Games (a feat P. T. Usha matched four years later) and was Japan's first individual women's 400 m champion.

This record stood for nearly thirty years,[8] with a Chinese team finally beating it at the 2015 IAAF World Relays.

She ran her individual finals faster than she had done four years earlier, but the standard of women's sprinting in Asia had improved and this meant she was fifth in the 200 m and third in the 400 m. P. T. Usha succeeded Isozaki in both disciplines with another Indian, Shiny Abraham, finishing ahead of the Japanese sprinter in the 400 m.[5] The Japanese short relay team fell to fifth in the rankings but the national long relay team remained competitive as Isozaki anchored home a quartet including Keiko Honda, Koshimoto and Ayako Arai to the silver medal behind the Indian women.

[4] Isozaki won a 200 m/400 m double at the Japan Championships in 1987 – the first time a female athlete had done this feat since the longer sprint was introduced to the national program in 1962.

She ran the anchor leg for both the 4×100 and 4×400 m relay teams, coming sixth the former but managing a final silver medal in the latter.