Why are pro cyclists’ legs so veiny?

"After sixteen stages I think my legs look little tired," wrote Pawel Poljanski in a post to Instagram. We’ve all had tired legs, but they don’t normally look like Pawel’s. Just why are pro cyclists’ legs so veiny?

Low body fat certainly contributes. When Team Sky published a photo of Chris Froome’s legs back in 2014, they described him as ‘ripped’.

Our man @chrisfroome is looking absolutely ripped ahead of #LBL on Sunday! (Photo: @michellecound) #VaVaFroome pic.twitter.com/UGePCkvwKU

— Team Sky  (@TeamSky) April 23, 2014

But the more extreme veininess tends to be seen after a stage. When Poljanski’s fellow Pole, Bartosz Huzarski, published a similar photo after the 18th stage of the 2014 Tour, he said: “I can see this view — maybe not every day — but still often, especially after a hard race at high temperature."

The cause, logically enough, is blood flow.

Dr Bradley Launikonis from the University of Queensland's School of Biomedical Science told ABC that elite cyclists will experience significantly higher blood flow to their legs compared to the average person.

“The amount of blood that we get normally going down to our legs is five litres per minute, for anyone at rest. For an untrained athlete, their maximum exercise will have 20 litres per minute flowing through the muscles.

“One of these elite cyclists will have double that, about 40 litres per minute. They have massive volumes of blood moving through.”

But surely the effort is over and blood flow will therefore return to normal? Not so, according to Launikonis.

"After he's finished exercising, the veins are showing up. Blood flow is pressurised through the arteries in a highly regulated fashion.

"What we're seeing are the veins, and there's a lot less pressure in them. There's a high level of blood being pushed into his legs for long periods of time, and it's still in there post-exercise.

"It's not going to happen to someone who's doing recreational exercise. It's clearly something that's only going to happen in elite athletes, like these guys riding in massive cycling events."