April 6, 2015 12:14 PM EDT

A Japanese woman is believed to be the first centenarian to complete a 1,500-meter swim in a 25-meter pool, CNN reports.

Mieko Nagaoka, 100, swam backstroke for 1 hour, 15 minutes and 54 seconds at a Japan Masters Swimming Association event in Matsuyama. Some reports say she has set a world record, but Guinness World Records has yet to verify it.

Nagaoka started swimming at age 80 to speed her recovery from a knee injury and has been known to train four times a week for two hours at a time, according to FINA, the international governing body for aquatic sports.

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Write to Olivia B. Waxman at olivia.waxman@time.com.

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