Sir Bradley Wiggins began his final event in Britain before retiring as he raced for the first time since his use of a banned steroid was revealed.
The 36-year-old is competing with Mark Cavendish in the madison at the Six Day London event, which finishes on Sunday.
Wiggins had three therapeutic use exemptions (TUEs) for medical reasons.
But some have questioned whether Wiggins and Team Sky acted correctly, although there is no suggestion any rules were broken.
Wiggins, Britain’s most decorated Olympian, will retire after next month’s Six Day track event in Ghent.
The UCI, cycling’s world governing body, cleared him to use the banned substance triamcinolone to treat allergies and respiratory issues.
Wiggins took the drug during his time at Team Sky, shortly before the Tour de France in 2011 and 2012 – which he won, becoming the first Briton to do so – and the 2013 Giro d’Italia.
His TUEs were approved by British authorities and the UCI. Both Wiggins and Team Sky have denied wrongdoing.
Team Sky, British Cycling and Wiggins are also co-operating with a UK Anti-Doping probe into a package that was delivered to the team during the 2011 Criterium du Dauphine, which Wiggins won.
Richard Conway, BBC Radio 5 live sports news correspondent
“Good to get back on a bike” is how Sir Bradley Wiggins put it when introduced by one of the Six Day Cycling hosts to a cheering crowd on Tuesday night.
With continuing questions over his use of TUEs and scrutiny over a mystery package delivered to Team Sky following a race in 2011, he opted not to speak with the media and remained out of sight in the warm-up area.
His partner for this event, Mark Cavendish, did talk. However, he wasn’t keen to discuss Wiggins, answering in curt sentences even when asked simple questions about taking to the track with the five-time Olympic champion.
This is a sport under pressure. And tonight the tension showed.