How big a physical impact does COVID have on a Tour de France rider?

Magnus Cort's COVID infection, in data and his personal observations.

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This Tour de France has been raced with the menacing threat of COVID-19 hanging over it. There were late substitutions right up until the Grand Départ in Copenhagen and in the weeks since 13 riders have tested positive including stage winners, team leaders, and vital domestiques.

One of those riders was Magnus Cort (EF Education-EasyPost), one of the key animators of the early stages of the race. Cort was clearly flying coming into the Tour de France. He was off the front in breakaways for more than 500 km, wore the KOM jersey for most of the first week and capped it with a win on Tuesday’s stage 10. Then, he started deteriorating.

A surprisingly complete picture of Cort’s changing condition exists – both from his reported impressions, and in the form of data released from his Whoop wristband.

Cort in the polka dot jersey earlier in the race.

Cort wrote on Saturday that “since Wednesday, I have had discomfort in my body”, but at that point had tested negative on several COVID tests. He was, he wrote, “lethargic”, with several other symptoms. “It has not been a fever, but it is as if many of the symptoms have overlapped the fatigue, so I cannot completely separate things,” he explained. Cort had also been struggling to get to sleep, despite his fatigue. Celebration on Tuesday night turned to sleeplessness thereafter. “Fatigue has set in in my head,” Cort wrote. “I feel used. It is hard mentally to ride such a long bike race. Especially in this insane heat.”

On Sunday morning, Cort had the answer as to why he had been feeling so unwell, returning a positive test after five days of symptoms. “Magnus Cort woke up this morning with a headache and fever and has since tested positive for COVID-19. He will not start stage 15 of the Tour de France. His medical evaluation is ongoing,” his team said on its social media.

Today, Monday, the exercise tracking company Whoop – a sponsor of EF Education-EasyPost – shared physiological data that supported Cort’s observed impressions.

The big picture metric is Cort’s recovery rate, how quickly he bounced back from one day to the next. For the first 16 days, Cort’s recovery averaged 57% from one day to the next. On the day of his COVID-19 positive, that dropped dramatically, to 19%.

His respiratory rate jumped up significantly, too – from 14.5 average breaths per minute, to 16.5.

Cort’s resting heart rate showed an even more dramatic spike. Over the five days leading up to the COVID positive, his resting heart rate slowly increased from 37 bpm, before spiking up to 47 bpm on the morning of his withdrawal from the race.

Correspondingly, his heart rate variability plummeted. This measure of the interaction between the parasympathetic and sympathetic nervous systems, measured in milliseconds, is, Whoop says, an important indicator of a body’s health. A low measure indicates that “your body is working hard for some other reason (maybe you’re fatigued, dehydrated, stressed, or sick and need to recover), which leaves fewer resources available to dedicate towards exercising [or] competing.” On stage 11, Cort’s range was 99 ms. By stage 14, as his body fought the burgeoning infection, it dropped to 87 ms. On stage 15, when he tested positive, it plunged to 61 ms.

Cort on Stage 10.

The final metric shared by Whoop was related to his fever symptoms. The Dane’s hot performances earlier in the race had disappeared, replaced by actual hotness. His skin temperature was, Whoop notes, “! very elevated”, increasing by 2.0° C.

The Tour de France has its final rest day today, in the baking heat of Carcassonne, where the remaining riders of the race will be resting in preparation for three days in the Pyrenees, a sprint stage, a time trial, and finally a celebratory spin down the Champs-Élysées.

By that point, hopefully, Magnus Cort and the other unlucky COVID-positive members of the peloton are feeling much better.

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