If you've been treating HYROX like a functional fitness competition with some running bolted on, new research suggests you're approaching it wrong. A 2025 peer-reviewed study on recreational HYROX athletes has confirmed what elite competitors have suspected for years: this is, at its core, an endurance sport. And the number that matters most isn't your sled push weight. It's your VO2max.
What the Research Actually Found
The study tracked heart rate and physiological markers across recreational HYROX competitors and found that athletes spent approximately 99% of their total race time at or above lactate threshold. That's not a rounding error. That's nearly the entire race, from the opening 1km run to the final SkiErg pull, sustained at an intensity where your body is working at or beyond its aerobic ceiling.
Lactate threshold is the intensity at which lactate begins accumulating in the bloodstream faster than your body can clear it. Spending a few minutes above it is hard. Spending the better part of an hour there, while also performing eight distinct exercise stations, is a physiological demand that most strength-focused training programs are not designed to develop.
More significantly, the researchers identified VO2max as the single strongest physiological predictor of finish time across the study group. Athletes with higher aerobic capacity consistently finished faster, across both the running segments and the functional stations. The correlation held regardless of strength levels, suggesting that raw aerobic fitness was the dominant variable separating faster from slower competitors.
Running Is 60% of Your Race. Train Accordingly.
Here's a number worth writing down: running accounts for approximately 60% of total HYROX race time. The eight 1km running segments that bracket each exercise station aren't transitions. They're the race. They determine your pacing, your recovery between stations, and ultimately, your clock.
That reframes the training calculus entirely. If you're spending the majority of your weekly sessions on strength work, skill work, and station practice, you're optimizing for 40% of the event. That's not a balanced approach. It's a structural mismatch between your training and the physiological demands of competition.
Building a genuine aerobic base through consistent running volume isn't glamorous, and it doesn't show up immediately on your Instagram. But the research is unambiguous: it's the highest-leverage investment you can make in your HYROX preparation. For context on how interval-based approaches compare to steady aerobic work, Sprint Intervals Beat Steady Cardio: 44-Trial Meta-Analysis breaks down the evidence across training modalities and helps clarify when each approach delivers.
Volume Beats Intensity (When It Comes to Endurance Work)
The study also found a strong correlation between higher weekly endurance training volume and faster HYROX finish times. This correlation was stronger than the correlation between strength training volume and performance. Put plainly: the athletes who ran more, rowed more, and logged more aerobic time each week were faster on race day, and that relationship was more predictive than how much they lifted.
This doesn't mean strength training is irrelevant. The functional stations require real muscular endurance and positional strength, and an athlete who can't control a heavy sandbag lunge will lose time regardless of their VO2max. But the research is pointing in a clear direction: if you're going to tip the scales of your training toward one modality, tip it toward aerobic volume.
A practical starting point for most competitive recreational athletes is a minimum of four aerobic sessions per week, with at least two dedicated running sessions that include structured pacing work at and below your lactate threshold. Threshold runs, tempo intervals, and progressive long runs all develop the aerobic machinery the event demands.
Why Strength-First Athletes Are Leaving Time on the Course
The conventional entry point into HYROX, especially for athletes coming from CrossFit or functional fitness backgrounds, is to treat it as a strength-and-conditioning test with cardio in between. The logic is intuitive: the stations look like gym exercises, the culture overlaps with functional fitness, and if you can move well under load, the running will come.
The 2025 data challenges that assumption directly. Athletes who build their HYROX training around strength volume without a corresponding aerobic base are likely undertrained for the dominant physiological demand of the event. They may feel strong at the stations but find themselves redlining during the running segments, which compounds across eight laps and compounds fatigue at each subsequent station.
This is also where VO2max becomes a practical concern rather than a theoretical one. VO2max determines how much oxygen your working muscles can utilize per minute. A higher ceiling means you can sustain faster paces at lower relative effort. That lower relative effort is what keeps your heart rate from spiking into unmanageable territory between stations and allows you to approach each exercise block with more capacity. If you're curious about how different HYROX formats affect these demands, Ultimate, Fast, Ultra: HYROX's 3 New Formats Explained outlines how race structure varies and what physiological profile each format rewards.
How to Raise Your VO2max Without Abandoning Your Strength Work
You don't have to scrap your strength training to address this. But you do need to be intentional about sequencing and volume distribution.
Several approaches are supported by the current evidence base:
- Zone 2 foundation work: Two to three sessions per week of sustained aerobic effort at a conversational pace builds mitochondrial density and improves your body's ability to process oxygen. This is the base layer that everything else sits on. Sessions of 45 to 75 minutes are effective for most recreational athletes.
- VO2max intervals: Short, high-intensity intervals at or above your VO2max pace (typically 3 to 5 minutes in duration) directly stimulate the adaptations that raise your aerobic ceiling. Two sessions per week during a build phase is sufficient for most athletes without accumulated fatigue becoming a problem.
- Threshold runs: Sustained efforts at your lactate threshold develop your ability to maintain the precise intensity that HYROX demands across its full duration. Twenty to forty minutes at threshold, once per week, is a high-return investment.
- Strength sessions as support: Keep two to three strength sessions per week with an emphasis on muscular endurance at the stations (higher reps, moderate loads, minimal rest). Absolute strength matters less than the ability to sustain output under accumulated fatigue.
Nutrition also plays a role in sustaining training volume at this level. Protein timing, particularly pre-sleep intake to support overnight recovery, becomes relevant when you're running multiple sessions per week. Casein Is the Protein You Keep Forgetting About covers the evidence on slow-digesting protein and why it's especially relevant for athletes managing high training loads.
Testing Your VO2max: Where to Start
You don't need a lab to get a working estimate of your VO2max. Most GPS running watches now provide an estimate based on heart rate data during runs, and while these aren't as accurate as metabolic testing, they're directionally useful for tracking progress over a training cycle.
Alternatively, a standard Cooper Test (run as far as possible in 12 minutes) provides a validated field estimate. Most online calculators can convert your 12-minute distance into a VO2max approximation. Track this every six to eight weeks during your training block to confirm your aerobic development is moving in the right direction.
If you have access to a sports performance lab or coaching facility, a proper incremental treadmill test with lactate sampling will give you precise threshold and VO2max data. In the US market, these tests typically run between $150 and $350 depending on the facility and protocol depth. That's a small investment relative to the training decisions it informs.
The Practical Takeaway
The 2025 research doesn't invalidate strength work or station-specific training. Both matter. But it draws a clear line under where the performance ceiling actually lives: in your aerobic engine, not your squat rack.
If your VO2max is limiting your HYROX performance, no amount of sled push practice will close that gap. The athletes who get faster year over year in this sport are the ones who treat their aerobic development as a non-negotiable priority and structure their training volume to reflect that. The research now confirms what they figured out through repetition.
Build the engine first. The stations will follow. And if you're supporting high training volumes with supplementation, Creatine Plus HMB or Hydration: Which Stack Actually Works? provides a clear evidence comparison to help you identify what's worth adding and what isn't.