Bora-Hansgrohe rider Pawel Poljanski broke the internet after Instagraming a photo of his “tired legs” following stage 16.

The sprawl of veins punching through his paper-thin skin looked like a host of spiders throwing a web-weaving rave. Heck. Even my mom reposted it asking, “Does this hurt?!” Other slack-jawed observers wondered if such a vascular look was worth aspiring to, or whether Poljanski was simply a freak of nature.

No, mom, it doesn’t hurt (though the efforts to get there usually do). The rest of the questions I turned over to vascular expert Debabrata Mukherjee, MD, chair of the department of internal medicine and chief of cardiovascular medicine at Texas Tech University Health Sciences Center in El Paso.

“These prominent veins are due to a combination of low body fat and significant increase in blood that flows through the legs of high level cyclists,” says Mukherjee. Tour de France riders have minimal body fat, so there’s no soft layer under the skin masking the veins, which are essentially sitting closer to the surface.

“High level cyclists also have double the blood flow to their legs compared to recreational exercisers,” he explains. So while you may have about 20 liters a minute coursing through your pistons as you ride, a pro like Poljanski pumps 40 liters a minute through his pedal pushing muscles. “That contributes to bulging prominent veins,” says Mukherjee.

And if those metabolic changes don’t pump you up enough, blood pressure increases during exercise can force plasma fluid out of your thin vessel walls and into compartments surrounding your muscles. This process, known as filtration, causes swelling and hardening of the muscle, which nudges all those bulging veins even further to the skin’s surface.

Should you aim to create your own vascular network to share on your social network? Not necessarily. Prominent veins in and of themselves are not particularly beneficial, and like diamond carved calves and second knee cap quads, not every rider is genetically wired to achieve the same aesthetic. But a few more veins rising to the surface is definitely an indicator of improving fitness, says Mukherjee.

“Since it reflects lower subcutaneous fat and higher blood volume, the harder a cyclist trains the more prominent the veins will become,” he says. “It is something that may tell an athlete that he/she is getting to a higher level of performance.”