How does cycling 3,483km in 21 days affect your body?

RTÉ News​

17-07-2025

Analysis: Completing the Tour de France route is a monumental achievement for any cyclist as it takes a serious toll on the human body
By Steve Faulkner, Nottingham Trent University
The Tour de France is often called the world's biggest annual sporting event. Each July, up to 12 million people line the roadside, while the cumulative TV audience tops 3 billion viewers across 190 countries.
In 2025, 184 riders will compete in teams of eight, racing a punishing 3,483 km route with nearly 50,000 metres of climbing, roughly the height of Mount Everest six times over. Over 21 stages, riders tackle time trials, flat sprints and brutal mountain passes through the Alps, Pyrenees and Massif Central. Irish cyclist Ben Healy is the current race leader and yellow jersey holder after 11 stages of the 112th edition.
Professional cyclists possess extraordinary endurance and are capable of generating high power outputs day after day. Yet, despite having far less training and support, a number of amateur cyclists have begun riding the Tour route in recent years just days before the pros.
The Tour 21 is one such effort and offers cyclists a chance to follow in the tyre tracks of the elite while raising money for a good cause. In 2021 I joined 19 others to ride the full route in support of Cure Leukaemia, with a shared goal of raising £1 million for blood cancer research.
As a blood cancer survivor diagnosed at 16, this challenge combined my love of cycling, my background in science and my deep desire to give back to the community that helped save my life. It was also a unique opportunity to study how amateur cyclists cope with one of the most demanding endurance events in the world.
The research findings were published in the Journal of Science and Cycling, to coincide with 2025's Grand Départ (the official start of the race) in Lille.
Training for the impossible
Originally, the study planned to include lab-based physiological assessments of the amateur cyclists undertaking the Tour de France route, but the pandemic forced us to adapt and rely instead on data from training diaries. These gave us insight into how much (or little) training had been done leading up to the ride, and how riders managed the physical and mental strain during the event itself.
From RTÉ Radio 1's Morning Ireland, Ben Healy takes the yellow jersey at the Tour de France, the first Irishman to do so since Stephen Roche in 1987
While professional cyclists typically train 20–25 hours a week – often at altitude, with tailored coaching and racing schedules – our group of amateurs had full-time jobs, were typically 15–20 years older than the pros and trained around seven to ten hours a week.
Our preparation was far from ideal, averaging just 47km per ride and 350 metres of climbing; a fraction of what the Tour demands. In fact, this amounted to less than 10% of the required climbing during the mountain stages.
Once the ride began, the contrast between training and reality was stark. The group averaged nearly seven hours of riding a day, a 300% increase from their usual routine. Within four days signs of overtraining began to emerge: riders were no longer able to elevate their heart rates, a classic marker of central nervous system fatigue and excessive physical stress.
From Global Cycling Network, how does the Tour de France impact rider health and fitness?
As the days progressed, performance metrics continued to decline: heart rates dropped, power outputs fell and mood scores deteriorated. The cumulative fatigue was undeniable.
Surprisingly, when we compared our amateur data to metrics from professional riders, we found that although pros ride at much higher power outputs, amateurs were subject to greater relative stress. On some days they spent almost double the time in the saddle, which meant they operated closer to their physical limits, with far less time for recovery – and often suboptimal sleep and nutrition.
By the final week many of the riders could no longer produce the same power they had in the first few days. In some cases, heart rates wouldn't rise above 100 beats per minute – a clear sign of accumulated fatigue and physiological overload.
How to prepare for an ultra-endurance challenge
If you're planning to take on a major endurance event – whether it's cycling, running, or hiking – here are some lessons from the road:
Train specifically for the event
Your training should mirror the challenge ahead. For the Tour, this meant preparing for long, back-to-back days with significant climbing. Mimic the intensity, volume and terrain as closely as possible.
Understand how quickly fatigue builds
Over multiple days, fatigue doesn't just accumulate – it compounds. Listen to your body, adapt your plan and include plenty of recovery time.
Prioritise nutrition and recovery
These two factors can make or break your performance. You'll need to consume enough energy to fuel the effort, but avoid excessive intake that leads to unnecessary weight gain. Recovery – through sleep, rest and refuelling – is equally vital.
Work with an experienced coach
More than fancy bikes or high-tech gear, a good coach is your best investment. They can help tailor your training plan, track your progress and adapt strategies as needed. Don't underestimate this support.
From Cheddar Explains, what the Tour De France does to a rider's body
Completing the Tour de France route is a monumental achievement for any cyclist — amateur or pro. In 2021, our team not only rode the full route, but also raised over £1 million for Cure Leukaemia. For me, it marked a deeply personal milestone in my cancer journey.
Throughout those 21 days, I thought often of the physical and emotional battles I faced during treatment; moments when I didn't know if I'd survive, let alone ride across France. That experience gave me the resilience to keep going, even when my body was screaming to stop.
Riding the Tour taught me that we're capable of far more than we realise, especially when we ride with purpose.