Athlete	Claire Stuijvenberg
Age	26
Profession	Campaign & Promotion Specialist
Background	Fitness
Goal	Run faster during HYROX
Start coaching	November 2025
Focus	Aerobic base, consistency and load tolerance
Result	HYROX time 1h29 > 1h17

The Challenge

When Claire came in for her first performance test, she had just completed her first HYROX Women’s Doubles in 1:29. Of that time, she spent 52 minutes running.

The biggest opportunity for improvement wasn’t on the sleds, the lunges or the wall balls.

It was in the running.

So the question wasn’t: How do we make Claire stronger at Hyrox?

The question was: How do we enable her to keep running faster between the stations?

HYROX Training: The Performance Test

We didn’t start with a training plan.

We started with testing.

Claire’s first performance test showed that her aerobic system still had significant room for improvement.

Results of the first performance test

	Speed	Pace
Aerobic threshold	7,2 km/h	8:20 min/km
Anaerobic threshold	9,4 km/h	6:23 min/km

The data pointed in one direction.

Not more intensity.

More aerobic training.

Claire’s aerobic base simply wasn’t strong enough. That had to change.

In other words:

Train Slower to Race Faster

My advice to Claire was probably not what she expected.

Not more interval sessions.

Not more high-intensity workouts.

Instead, the assignment was simple: Spend as much training time as possible in Zone 2.

Easy endurance sessions. Controlled, consistent and deliberately paced to build a stronger aerobic engine.

sAlongside those sessions, Claire completed one HYROX-specific workout each week, where high intensity was encouraged.

Only during the final four weeks before race day did we introduce lactate shuttle intervals, designed to prepare her for the repeated transitions between running and the workout stations.

It may sound boring.

But Claire fully committed to the process and executed it almost perfectly.

In TrainingPeaks, nearly every planned workout turned green—a sign that she had not only completed the session, but also stayed within the prescribed training intensity.

And that made all the difference.

Seven Months Later: The Retest

The second performance test revealed something remarkable.

Both Claire’s aerobic and anaerobic thresholds had improved significantly.

But one result stood out.

Claire became the first athlete I had ever tested whose new aerobic threshold exceeded the anaerobic threshold from her first test.

In other words, after seven months of training, she could sustain a pace aerobically that had previously only been possible near her anaerobic threshold.

That represents far more than just an increase in fitness.

It reflects a fundamentally stronger aerobic system.

Second Performance Test

	Speed	Pace
Aerobic threshold	7,2 > 9,5 km/h	8:20 > 6:19 min/km
Anaerobic threshold	9,4 > 10,5 km/h	6:23 > 5:43 min/km

That meant that seven months later Claire could comfortably sustain a pace that, before the training period, was only achievable around her anaerobic threshold.

That isn’t a marginal improvement.

It reflects a fundamentally stronger aerobic system.

The Proof Came on Race Day

The physiological improvements translated directly into Claire’s HYROX performance.

First HYROX Women’s Doubles

• Running time: 52 minutes
• Overall time: 1h29

After Seven Months of Training

• Running time: 43 minutes
• Overall time: 1h17

Claire cut nine minutes from the running sections alone.

And because she arrived at every workout station less fatigued, her station times improved as well.

The result was an overall improvement of 12 minutes.

What Other HYROX Athletes Can Learn

Many athletes believe the fastest way to improve is simply to train harder.

In reality, the opposite is often true.

A stronger aerobic base allows you to:

• recover faster between workout stations;
• maintain a higher running pace throughout the race;
• clear and reuse more lactate as fuel;
• keep running strongly in the final kilometres instead of slowing down.

Training this way requires discipline.

Easy running often feels too easy.

But Claire’s results show that trusting the process pays off.

HYROX Training: The Key Takeaway

The biggest gains don’t always come from adding more intensity.

More often, they come from applying the right intensity at the right time.

A HYROX race isn’t won by the hardest workout of the week.

It’s won by the hundreds of easy kilometres that build the aerobic engine required to sustain a high pace throughout the race.

A stronger aerobic system doesn’t just make you run faster.

It also increases your ability to clear and utilise lactate, allowing you to arrive at each workout station fresher and perform at a higher level.