The Brutal Physiology of Modern XCO
Why technical mastery is the ultimate recovery tool in a sport defined by 5-second bursts and during 90% of max average heart rates.
The latest episode of the D-VELO-P cycling training podcast dives deep into the high-octane world of Olympic Cross-Country (XCO) mountain biking. Fredrik and Erik break down a brand-new 2026 systematic review by Gabriel Protzen and colleagues that explores how the sport has evolved from the grueling endurance tests of the 90s to the punchy, technical sprints of today.
Here are the key takeaways from their discussion on the physiology of modern XCO.
1. The Death of the 2+ hour races
XCO has undergone a radical transformation. In the late 90s, races often stretched past the two-hour mark—Fredrik recalls racing the 1999 U23 World Championships in Åre, where the winning time was 2:19, and he finished in 2:43. Today, those same races are targeted at 80 to 100 minutes for elites and roughly 75 minutes for U23s. This shift has fundamentally changed the physiological profile required to win.
2. The “Stochastic” Nature of Power
Mountain biking isn’t a time trial; it’s a series of hundreds of micro-sprints. The study found that a typical race consists of roughly 334 efforts above maximal aerobic power, averaging just 4.3 seconds each, with only about 10.9 seconds of “rest” in between.
The “Rest” is a Lie: Even when not pedaling, riders are pumping terrain and navigating obstacles, keeping their heart rate at a staggering 90% of max for the entire race.
The 5/25 Workout: Fredrik describes a brutal simulation of this: 90 sets of 5-second sprints with 25 seconds of easy pedaling. By the end, your heart rate and lactate look exactly like a steady-state time trial, even though the power output is wildly inconsistent.
3. By the Numbers: The Tier 5 Athlete
What does a world-class (Tier 5) XCO rider look like? According to the review:
Body Comp: Men average 66kg and 179cm; Women average 56kg and 162cm.
Engine: Elite men boast a VO2 Max of around 82, while the reported average for women was 64 (though the hosts note that top-tier riders like Jenny Rissveds have significantly higher values).
Punch: Max aerobic power for men is roughly 6.6 watts per kilo.
4. Technical Skills = Physiological Recovery
A major gap in current research is the impact of technical skill. We argue that as riders fatigue, they lose the ability to execute the short bursts needed to maintain speed over obstacles. The best riders aren’t just the fittest; they are the ones who can maintain “solid lines” and technical precision in the final lap when everyone else is “skipping bursts” to save energy.
5. Training for the Modern Era
We emphasize that “stating the obvious” in research is helpful for validating training methods. To succeed in modern XCO, they recommend:
High Torque Intervals: Because XCO often requires high power at low cadences, training should include low-cadence, high-intensity efforts to build torque capacity.
Upper Body Strength: While most studies focus on legs, XCO requires significant upper body strength for bike handling and preventing the common “mountain biker back pain”.
The “Relic” of Fast Starts: While tradition dictates going “all out” from the gun, modern courses allow for more overtaking. The hosts suggest there is often more to be gained through disciplined pacing than a suicidal 60-second sprint at the start.
Final Thought: Whether you’re an “old school” rider from the 2-hour era or a “contemporary” racer, the science is clear: XCO is one of the most cardiorespiratory demanding disciplines in all of sports. Success isn’t just about having a big engine; it’s about having the mental and technical grit to use it 334 times in a row.
Listen to the full discussion on the D-VELO-P cycling training podcast.