The Biological Demands On The Body Of A Rider In The Tour de France

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Exercise scientists have declared that the Tour de France is the hardest endurance event in the world, but what does that actually mean? To help understand, longtime pro-cyclist trainer and researcher Iñigo San Millán, PhD, explains what is going on inside the riders as they make their way across 3,500 km (2,200 mi) over 3 weeks in July.

Stress Hormones Skyrocket

Production of stress hormones like cortisol rises pretty much out of the gate, says longtime pro-cyclist trainer and researcher Iñigo San Millán, PhD, director of the Exercise Physiology and Human Performance Laboratory in Boulder, Colorado.

“The first week is extremely nervous. It’s intense and stressful and riders aren’t sleeping very well,” he says. All of this sends their cortisol levels through the roof. Unless they are able to relax and recover during that first week, the elevated stress hormones will make them prematurely catabolic (i.e., their muscle tissue breaks down), which is bad news because they’ll need every ounce of muscle they have to make it through the Tour de France’s three grueling weeks of riding.

Muscles Break Down 

Exercise-induced muscle damage is sometimes all Tour riders face, says San Millán.

“Though many make it through the first week pretty well if they stay on top of their fueling and recovery, eventually many become catabolic as they head into the mountains,” he says. While in the first week riders may burn just 3 to 5 percent of protein stores (i.e., their muscles) to fuel their efforts, he says, by the final week they’re likely to burn up to 15 to 20 percent as their muscles become increasingly damaged, catabolic, and less able to store and supply glycogen.

Glycogen Storage Capacity Diminishes

About that glycogen: Despite eating diets composed roughly 75- to 80-percent of carbohydrates, San Millán says—with a whopping 25 percent of calories (or 2,000 calories out of the 6,000 to 9,000 they’re eating each day) being simple sugars—Tour riders have a hard time keeping up with their fueling needs by midway through the Tour.

“They’ve sustained so much muscle damage, their muscles no longer have the same capacity to store it,” he says.

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Hemoglobin Levels Drop

You rip through 200 billion red blood cells every day when you’re not desperately dangling off the peloton on the 17th hairpin turn up Alpe d’Huez. When you’re not under such duress, you also can create more red blood cells and soldier on.

Not so much during the Tour, when athletes’ blood simply can’t keep up with the mass destruction.

“[Riders’] oxygen-carrying capacity as measured by their hemoglobin concentration decreases from a healthy 15 or 14 grams per deciliter at the start [of the Tour] to 12 to 13 grams per deciliter by the time they cross the finish line in Paris,” says San Millán. Not only does that make them pseudo-anemic, but it also impairs their immune systems, so they’re more vulnerable to getting ill as the Tour wears on.

​Free Radicals Increase

Today’s athletes generally aren’t advised to take antioxidant supplements, now that we know popping these pills actually interferes with important training adaptations—like your body’s ability to generate its own natural antioxidants—and can lead to performance detriment rather than enhancement. The Tour is a different beast, however, says San Millán.

“Between the second and third week the body starts losing its ability to produce enough antioxidants to keep up with the daily six-hour free-radical onslaught,” he says, which also impedes immunity. In this case, some antioxidant supplements may be in order.

Heart Rate Declines

During the first week of the Tour, riders can hit their max heart rate no problem. Especially during those first three to five days, they’ll look down and see 190bpm or so and feel stoked.

By the last week, though, they may be excited to see numbers in the 160s to 170s, says San Millán. A lower max heart rate means your heart cannot beat fast enough to keep up with the work you’re doing, and results from being overtrained.

Regardless, the riders will probably be most excited to see the finish line on the Champs-Élysées, so they can finally give their heart and the rest of their tattered bodies a well-earned rest!

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