A picture is often described as worth a thousand words and that idiom has never been truer than the image shared by Polish cyclist Pawel Poljanski.

A thesis could be written on the rigours of the Tour de France, but Poljanski's photo, showing legs riven with veins that look poised to burst and skin frazzled by the sun, says it all.

"After sixteen stages I think my legs look little tired," the cyclist wrote on Instagram alongside the picture.

The picture, which quickly went viral, drew a huge response as users expressed concern at the state of his pins.

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"That can't be healthy," one horrified user wrote.

The cyclist is not the first to show the impact that long-distance cycling has on the body.

After sixteen stages I think my legs look little tired 😬 #tourdefrance

A post shared by Paweł Poljański (@p.poljanski) on

Chris Froome, who is currently leading the Tour, displayed his bulging veins in 2014.

The 27-year-old, who rides for Bora-Hansgrohe, is currently 75th in the general classification, after finishing 66th in the 16th stage between Le Puy-en-Velay and Romans-sur-Isere.

Dr Bradley Launikonis, from the University of Queensland's School of Biomedical Science, explained what happens to the legs during long-distance cycling.

"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," he told the ABC.

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

"The blood can pool there and that's what's happening in this extreme case. There is blood pooling in his veins which is why you're seeing them (so visibly)."