According to an article published by Dutch newspaper De Telegraaf and publicised by Cycling Weekly, rumours have even been circulating that one team within the Tour de France are giving their riders a banned doping agent, sometimes without the rider’s knowledge.
This news comes while the sport is still recovering from a dark history dramatically highlighted by disgraced American cyclist Lance Armstrong, who is serving a lifetime ban from cycling after admitting to doping which ultimately stripped him of his record seven Tour titles.
Both media outlets reported that Aicar, a muscle-enhancing and fat-burning drug is being delivered in powder form, dissolved in water, cola or an energy drink via the rider's water bottle.
Despite being produced naturally by the body, which makes detection for artificial forms difficult, Aicar is a banned substance and the rumours have anti-doping agencies on high alert.
“I am not surprised that Aicar is used in cycling. It can also be no coincidence that a few WADA laboratories have recently been warned about Aicar and that murmurs are now coming from cycling," said Professor Peter van Eenoo, who is the director of a World Anti-Doping Agency-affiliated lab in Ghent, Belgium.
“A request has been made to make greater efforts to track down Aicar. We had put research into this product on the back burner because we no longer saw it as a major problem.”
Meanwhile, De Telegraaf has also reported on Jumbo-Visma's use of Ketone supplements, which are "not on the prohibited list" stated team manager Richard Plugge.
"Ketones are a dietary supplement," he said. "You can use them just like vitamins. The substance is not on the prohibited list, and it's also known that other teams use ketones."
Race debutant Wout van Aert's Stage 10 victory on Monday gave Jumbo-Visma its 38th win of the season, including the Dutch-registered UCI WorldTour team's fourth victory at this year's Tour, which kicked off with an opening stage win by Mike Teunissen, a Stage 2 team time trial victory and a Stage 7 sprint win from Dylan Groenewegen.
Ketones are produced naturally by the liver once there are no carbohydrates to burn, thus forcing fat stores to be utilised as an energy source. Synthetic ketone supplements, used in conjunction with a low-carb diet, are thought to provide an added energy source that helps preserve glycogen storage, reduce lactic acid and aid in recovery.
A recent study out of the University of Leuven in Belgium links ketone supplements to a 15 per cent increase in performance for endurance athletes. According to De Telegraaf, Professor Peter Hespel had 16 subjects ride a mini Tour de France while ingesting ketones, and later said that the substance had an "unprecedented effect on recovery" and that the "performance capacity also increases considerably."
The use of ketone supplements in pro cycling dates back to the 2012 London Olympics, and with both Team Sky and QuickStep being linked to its use in previous years.
With little knowledge surrounding the long-term effects of ketone supplement use, not all teams have bought into its practice.
"We think there should be more clarity about the effects of this medicine on the health of the athlete in the long term," Sunweb team doctor Anko Boelens told De Telegraaf. "In addition, there is much uncertainty about the efficacy. There are even studies that show that it has a negative effect on sports performance. That the remedy would only be good for recovery. We want to be sure that we will not harm our riders. "