Australian middle distance runner Jess Hull described her foray into the 800m at the Tokyo World Championships as a "fun little side quest".
Two-time Olympic gold medallist Femke Bol merely calls it "the next challenge".
Dutch 400m hurdles superstar Bol announced in a social media video that she would make the step up to the 800m next season, adding another dimension to one of the sport's most thrilling events.
"It's time for a new chapter," Bol said in the video.
"It's going to be an extra lap. I'm moving to the 800m."
Bol is a two-time 400m hurdles world champion, defending her title in Tokyo last month.
She also won bronze at the 2021 and 2024 Olympic Games in the event.
In both finals, she finished behind American superstar Sydney McLaughlin-Levrone, who won consecutive gold medals.
The pair have dominated the women's 400m hurdles event, running the nine fastest times in the history of the event between them.
However, McLaughlin-Levrone has turned her attention to the 400m flat. She won world championship gold in Tokyo and threatened one of athletics longest-standing world records at the same time.
"I've learned so much from hurdling and really loved it, it will always have a special place in my heart," Bol said.
"But I'm ready for the next challenge, a new stimulus, a completely different kind of race.
"It's different from what I'm used to ... and I'm really excited to explore that."
Bol has won each of the past five Diamond League annual titles in the 400m hurdles, as well as spectacularly anchoring the mixed 4x400m relay to gold in Paris.
Rivals rejoice at Bol's step up
Olympic 800m champion Keely Hodgkinson wrote a reply to the video saying, "Can't wait to share the startline" with two heart emojis.
World championships silver medallist Georgia Bell has dropped down to the 800m from the 1,500m where she won bronze in Tokyo.
She wrote, "So exciting Femke! Some serious global finals pending".
New Zealand's Zoe Hobbs wrote, "Love this! So excited for you!" while Poland's Pia Skrzyszowska just wrote "You craaaaazy".
"I've always loved this quote, 'If your dreams don't scare you, they're not big enough'," Bol said.
"And I think that's definitely the case here."
Bol's decision potentially puts her on a collision course with a number of rising Australian middle-distance runners.
Hull is the current Oceania record holder in the 800m with 1:57.15, a time she set by becoming the first Australian woman to make the final of both the 1,500m and the 800m at the same world championships.
However, she described the 800m as "an extra bit of fun" to help her top-end speed for the 1,500m, which remains her focus.
Australia had three runners alongside Hull line up in the 800m in Tokyo: Sarah Billings, Abbey Caldwell and former record holder Claudia Hollingsworth.
No modern historical precedent
Although switching between the 1,500m and 800m is relatively common throughout history, there have been far fewer instances of athletes having success changing between one and two lap events, outside of relays.
Alberto Juantorena of Cuba is the only man to claim the 400m/800m double at the same Olympics, doing so in 1976.
Jamaica's Arthur Wint claimed gold in the 400m and silver in the 800m at consecutive Games in 1948 and 1952. South African Bevil Rudd won the 400 and finished third in the 800m in 1920.
No woman has won both events at the Olympics. The women's 400m was run for the first time only in 1964 and the 800m regularly appeared from 1960.
However, Ann Packer won silver in the 400m, behind Australia's Betty Cuthbert in 1964, while also winning gold in the 800m.
Czech athlete Jarmila Kratochvílová, who won both events in the 1983 World Championships, still holds the 800m world record set at that competition.
Bol and McLaughlin-Levrone are not the only athletes to have made the successful transition from the hurdles to the flat, with Australian Jana Pittman, British runner Sally Gunnell and American Edwin Moses among several to have done so.
