Some are doing it for weight loss while others are gearing up for even tougher races.
But whatever the reasons for the runners to pound the ground in tomorrow's Great Eastern Women's Run (GEWR), they hope to cross over into new territory.
Take Vivian Tang, for example.
The 45-year-old started running in a bid to lose weight and took part in every single GEWR, which is now into its 10th edition.
Said the 1.5m tall stock-broker: "I started running 21 years ago to lose weight but it has now become a habit."
She weighed 50kg when she first started running and has since slimmed down to 42kg.
Tang had always tackled the 10km category in the previous nine editions of the GEWR but wants a crack at the 21.1km half-marathon this time.
She said: "I usually do other half-marathons the month before (in October)."
This year, however, she was away in Britain for leisure. Tang took part in two short races there so she decided to compete in the 21.1km category in the GEWR this year.
She will be one of five local runners in the closed elite category for the half-marathon.
The other Singaporeans include national runner Mok Ying Rong and Ironman triathlete Lim Bao Ying. The 22-year-old, who is the younger sister of marathoner Ying Ren, said: "The aim for me this year is to achieve a new personal best.
"I also want to push my timing to be as close to the Olympic qualifying time as possible but my main priority is to represent Singapore at the World Half Marathon Championships."
The event will be held in Cardiff next March.
There will also be an open elite category which will see 12 overseas runners compete for prize money of US$8,000 (S$11,200) and a crystal trophy.
Participants include Olympian Iuliia Andreeva from Kyrgyzstan as well as runners from China, Taiwan and North Korea.
The strong field is welcomed by the competitors.
Mok said: "They (the organisers) always bring in great athletes from all over Asia and from Singapore so I get to challenge myself against the best in Asia."
She noted that "the standard is pretty high and it is a very good opportunity to push myself".
Lim agreed, saying: "It is always competitive to run against them and regardless of who the competitors are, I'll always run my best."
With the haze a lingering concern, the race organisers will provide two updates regarding the weather conditions - one at 8.30pm today and another at 2.30am on race day.
The updates can be found on the event's Facebook page and at greateasternwomensrun.com.
In the event of a cancellation - when the three-hour Pollutant Standards Index rises above 100 into the unhealthy range, participants of the run with local-registered mobile phone numbers will also be notified via SMS.
Tomorrow's event, in the scenic Marina Bay area, has attracted 17,000 runners.