Two athletes from the stable of Mo Farah's coach Alberto Salazar say they have "never seen anything" to connect him with doping allegations.
Salazar, 56, is accused of violating anti-doping rules, although none of his athletes have ever failed a drugs test.
American Shannon Rowbury and Canada's Cam Levins defended Salazar against the claims.
One allegation concerns Olympic 10,000m silver medallist Galen Rupp, a training partner of Briton Farah.
There is no suggestion double Olympic champion Farah, who is part of Salazar's Nike Oregon Project (NOP) training operation in the United States, has broken any rules.
A BBC Panorama investigation in collaboration with US journalism organisation ProPublica claims that American distance runner Rupp, 29, was given the banned anabolic steroid testosterone in 2002, when he was 16 years old.
Salazar and Rupp deny any wrongdoing.
No allegations were made against other NOP athletes in the investigation.
Middle-distance runner Rowbury, 30, said: "Alberto has been a really great coach to me, I've never seen anything to make me question him or my team-mates."
On Sunday, Josh Rohatinsky, who ran for NOP from 2007 to July 2009, backed the "full extent" of the allegations, claiming former team-mate Rupp's improvement from 2006 to 2012 was "highly suspicious". He also spoke of "a wall of separation between Alberto and Galen with the rest of the group".
Rowbury said: "I've never cheated, I never would, I'd rather quit the sport than do that."
Canadian distance runner Levins, 26, who won 10,000m Commonwealth bronze last year, said: "I've only been part of the group for a couple of years and it seems to me all the allegations are before that time but there is nothing I've ever seen that I would attribute to any of these allegations.
"I've never been pushed into anything considered a grey area and I trust them, they've never given me a reason not to."