The Polish rider posted an extreme looking image of his legs after a Tour de France stage, but why exactly were his legs so veiny?

Following Tuesday’s stage 16, Bora–Hansgrohe rider Paweł Poljański left jaws dropping across social media when he posted a photo of his gruesomely veiny legs.

Like protuberant tree roots surging up against the skin, criss-crossing his quads and calves, it was certainly an arresting image. But what was the physiological explanation? Surely it couldn’t be healthy?

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Pundits emerged from all quarters to chip in their views on the how exceptional (or not) Poljański’s legs were. The Times’ resident doctor, Mark Porter, ventured to temper the hype by suggesting that the veiny-ness on display was in fact quite normal.

“Although the image looks an extreme example,” wrote Porter, “this is exactly what happens in all of us after exercise in warm conditions. You just can’t see it because most of us have much more body fat than Poljanski.”

Fair enough: as a professional rider, Poljański has very little body fat, probably no more than six to eight per cent, but was this really an adequate explanation? Plenty of riders are very lean, but rarely do we see legs with such startlingly bulging bloodlines.

“The notion that we’d all have legs like that if only we were skinny enough isn’t really correct,” says exercise physiologist Dr Jamie Pringle. The truth, as ever, is more complicated than the tabloids’ brisk explainers would have us believe. Just as important as leanness are athletic adaptations in the vascular system.

“In athletes, we see exceptional vascularisation,” Pringle continues. “That means greater non-visible capillarisation within the muscle, but also greater visible vascularisation at an arterial and venous level.”

Pawel Poljanski at the 2017 Tour de France (Sunada)

In other words, the gruelling training undertaken by a pro cyclist expands both the supply of oxygenated blood to the muscles and the extraction of deoxygenated blood, via veins, back to the heart and lungs.

“There is not more piping as such, but greater arterial diameters and definitely greater flow and dilatation — in response to the muscle’s demand for blood and oxygen.”

Bear in mind, when he took the photo, Poljański had just ridden the punishing 165km from Le Puy-en-Velay to Romans-sur-Isère in blustery conditions and finished a mere 1min 43sec behind stage winner Michael Matthews. His leg muscles had been screaming for blood for hours.

A super-adapted blood-supply network is no great advantage in itself, nor does it account for super-veiny legs — the major factor is having more blood.

“An extremely well trained athlete has far greater blood volume as a whole, referred to as hypervolemia,” says Pringle. “Because of that, their veins are simply fuller. That’s the key difference between your legs or mine and Poljanski’s.”

We’re not talking a few drops of blood, either — the difference is substantial.

“An untrained person has around five litres of blood, typically around 50 – 75ml per kilo — five to seven per cent — of body mass. A world-class endurance athlete can have two or three litres more in total, and as much as 150ml per kilo — 15 per cent — of body mass. Quite simply, Poljanski has twice as much blood in his body compared to the average Joe.”

Double the blood! No wonder pro riders’ legs occasionally look set to burst.