Fitness coach and former national triathlete Poon Pek Ya was fined $4,000 on Monday after pleading guilty to causing grievous hurt to a motorcyclist by negligent cycling.

Poon, who trains others in different sporting activities including cycling, was riding her bicycle along Changi Coast Road at around 7.30am on March 5 last year when she cycled across three lanes and stopped at a centre divider.

Motorcyclist Syed Mohammed Atheer Ahmad Reda Shahab was riding his bike along the centre lane of the three-lane road at around the same time, the court heard.

Deputy Public Prosecutor Selene Yap said: "The accused then cycled out into the centre lane of Changi Coast Road, in the direction of Telok Paku Road. In order to avoid the accused, the victim swerved to (his) right and fell to the ground. The victim then heard a cracking sound in his leg."

A medical report revealed that Mr Mohammed suffered a fracture to his right shin. He was given hospitalisation leave from March 5 to Aug 7 last year.

Poon, 48, founded fitness training company Unpossible in 2013. According to her firm's website, she has won many awards for her sporting achievements. For instance, she won second place in the 2013 Port Dickson International Triathlon and was the champion in the 2001 Al Formosa International Triathlon.

Poon was represented by lawyers A. Sangeetha and Tan Jun Yin. Their mitigation plea stated that except for a parking offence in 2005, this was Poon's first brush with the law.

The defence lawyers added: "In the course of her career, Pek Ya trained school teams from Temasek Polytechnic, Edgefield Primary School and Nanyang Technological University between 1999 and 2013.

"In Pek Ya's... years of experience, neither Pek Ya nor any student under her care has ever been involved in a cycling accident."

Before handing out the sentence, District Judge John Ng said he thought the offence was due to a misjudgment on Poon's part.

For causing grievous hurt due to negligence, Poon could have been jailed for up to two years and fined up to $5,000.