Bare feet pounding the pavement, Ranjith Vijayan barely breaks stride as he overtakes joggers at Bishan Park.
But his gaze is not fixed on the path ahead.
Rather, he looks down, deftly twisting a Rubik's cube, easily solving the three-dimensional puzzle in less than 30 seconds.
Then, as the 37-year-old software engineer runs, he scrambles the cube - invented in 1974 by Erno Rubik, a Hungarian professor of architecture - back into random colours once more.
It is a challenging combination of athletic prowess and spatial-reasoning skills, but Vijayan is far from done. On Dec 6, he will run the Standard Chartered Marathon Singapore and attempt to solve the Cube at least 176 times or more during the race.
His aim is to break the Guinness world record for the most Rubik's cubes solved while running a marathon.
The record is 175, achieved by American Shane White at the 2012 Rock 'n' Roll Savannah Marathon in Savannah, Georgia. He clocked 4hr 53min 39sec, complying with the five-hour stipulation required for a valid record attempt.
Speaking to The Straits Times, Vijayan said he is confident of bettering White's record and aims to solve at least 300 cubes during the StanChart run, which will be only his second marathon.
Solving a solitary cube used to take him nearly as long as the time he now takes to run the full distance of 42.195km.
The father of two picked up his first cube in 2001 and then progressed to "speedcubing", or solving a Rubik's cube as quickly as possible.
He has spent an estimated $1,000 on his hobby, having purchased cubes from Indonesia, Japan and China during business trips.
The mere thought of running a full marathon might leave some fatigued, but Vijayan said he began using the cube to combat the monotony of distance running.
"When I started running (in 2014), I found it very boring," he said. "You can count trees or count people or listen to music. But nothing really worked for me.
"I found that by running with a Rubik's cube, I could run longer distances without stopping."
His first race with a cube was the Standard Chartered Half Marathon in December last year, which he finished "comfortably". Then, the cube was a mere diversion to keep him occupied.
This time, he will be followed by a photographer, videographer, two pacers and a helper to hand him "scrambled" cubes.
The logistics of carrying out and verifying the feat during a major race, in accordance with stipulations by Guinness, are being handled by race organisers.
Although she is not a big fan of Rubik's cubes, Vijayan's wife Zhang Xiaohang will be waiting for him at the finish line.
"Sometimes when she gets angry, she scrambles my cubes," he said.
Their four-year-old son will be participating in the 700m Kids' Dash event on Dec 5.
Vijayan, who only started running barefoot this year, now runs an average of 40km a week, usually training at Bedok Reservoir.
"I used to believe sports and athletics are for a certain set of people," said Vijayan, who admitted he had little interest in sport until he started running.
"I want to prove that guys like me can also run marathons."
What about the Rubik's cube? No problem - he's got that aspect in hand, literally and metaphorically.
Matthew Mohan
WATCH THE VIDEO ONLINE
See how Ranjith Vijayan solves a Rubik's cube while running http://str.sg/ZaRT
