SINGAPORE - One of the first instructions Ting Chun told the 15 amateur cyclists he oversees at a local cycling club was to train indoors or ride unaccompanied after the Government's circuit breaker measures took effect last week.

To the 35-year-old supply chain executive's dismay, he noticed other cyclist enthusiasts here were not taking the new rules seriously. While out on his solo outings, Ting saw big groups of cyclists travelling together.

This trend led the Singapore Cycling Federation (SCF), after feedback from Sport Singapore and other government agencies, to issue a reminder on Facebook on Saturday (April 11) that "all cycling if done outdoors must be carried out either alone or with individuals of the same household" and "between different household units of cyclists , please leave 20m of spacing, even at traffic lights."

The SCF told The Straits Times on Sunday it strongly recommends all cyclists stay home as far as possible during this period and the 20m gap was a guideline and based on a recent white paper from the Netherlands' Eindhoven University of Technology and Belgium's KU Leuven on the spread of the coronavirus.

The scientists noted those walking behind someone should keep 4m to 5m away instead, while those running or cycling slowly behind someone doing the same should keep at least 10m away. This distance extends to 20m if one is cycling at high speeds.

This is because of the air currents produced by the person in the front, also known as a slipstream.

The SCF also noted: "As the 20m is merely a guideline from an academic paper and not a mandatory rule of law, it would not be correct to speak of enforcing this guideline as a strict rule of law."

Dr Piotr Chlebicki, a Mount Alvernia Hospital infectious disease specialist who also cycles recreationally, was surprised by the 20m advisory.

He said: "It is safer for cyclists to be apart for 1m because they are moving faster than pedestrians in an open space. The discussion about micro-droplets in slipstreams is based on laboratory settings and is not transferable to real life.

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"Bike or no bike, to avoid meeting people other than those you live with in the same household is the main rule of social distancing to break the chain of contagion and stop the virus spreading."

Dr Leong Hoe Nam, an infectious diseases specialist at Mount Elizabeth Hospital, was also sceptical of the effectiveness of the 20m spacing and said a 1m gap was sufficient.

But with the public still forming crowds and disregarding the 1m social distancing rule, he said, the authorities may have to implement stricter measures.

The current situation cannot continue, said Ting.

"It is a shame because if everyone can follow the rules, then we can still exercise through cycling on our own or with those from our household.

"But if there continues to be people who wilfully cycles in groups outside of their household, then it is just a matter of time cycling is totally banned during this period."