How to Improve VO2 Max for Hyrox and Endurance | BOD – We Are BOD Inc.

If you've ever hit the wall during a Hyrox race, legs turning to concrete somewhere between the sled push and the fourth 1 km run, the problem was probably oxygen. More precisely, it was your body's ability to deliver and use oxygen under sustained, mixed-modal stress. That ability has a name: VO2 max. VO2 max is the single most-cited metric in endurance sports for good reason. It represents the ceiling of your aerobic engine, which is the maximum rate at which your body can consume oxygen during intense exercise, measured in milliliters per kilogram of body weight per minute (ml/kg/min). A higher ceiling means you can work harder before your body shifts into anaerobic overdrive and starts accumulating fatigue debt you can't repay mid-race. For Hyrox athletes specifically, understanding how to raise that ceiling is the difference between surviving a race and competing in one.

Why VO2 Max Matters More Than You Think for Hyrox

Hyrox isn't a VO2 max test. Nobody is sprinting at 100% of their aerobic capacity for the full race. But that fact actually makes VO2 max more important, not less, because VO2 max determines the size of the engine from which every other performance metric is derived. Almost 70% of a Hyrox race is endurance-based, and running alone accounts for more than 50% of total race duration. The eight functional workout stations are themselves heavily dependent on aerobic energy contribution. Oxidative phosphorylation within the mitochondria powers most of the work during these stages, as the race wears on and glycolytic pathways become increasingly depleted.

VO2 max effort captured as a group of athletes cheer on a teammate powering through an all-out assault bike sprint.

Your lactate threshold is expressed as a percentage of your VO2 max. If your VO2 max is 45 ml/kg/min and your threshold sits at 80% of that, you can sustain roughly 36 ml/kg/min before things start falling apart. Raise your VO2 max to 55 ml/kg/min with the same threshold percentage, and now you're sustaining 44 ml/kg/min, a pace that would have buried you before is now comfortable.

The Polarized Approach: Why 80% of Your Training Should Feel Easy

One of the most counterintuitive findings in endurance science is that elite athletes spend the vast majority of their training time at low intensity. The best endurance athletes in the world follow roughly an 80/20 intensity distribution, about 80% of training volume at low intensity and 20% at high intensity, with very little time in the moderate "grey zone" in between.

A 2024 systematic review with meta-analysis compared polarized training against other intensity distribution models across multiple endurance disciplines. The researchers found that polarized and threshold training were the most effective approaches for improving endurance performance, with polarized training producing superior responses compared to high-volume, low-intensity-only programs during certain training phases.

For a Hyrox athlete, this translates to a weekly structure built around three to four easy sessions and one to two hard sessions running at tempo pace every day, doing MetCon workouts that leave you moderately fatigued but never fully recovered. This is where most recreational Hyrox athletes get stuck. You accumulate fatigue without providing the precise stimulus needed for either aerobic base development or VO2 max expansion.

Zone 2 Training: The Foundation You Can't Skip

Zone 2 training has received enormous attention in the endurance and longevity communities over the past few years, and the science backing it up is solid. This refers to exercise performed at roughly 60–70% of maximum heart rate, an intensity where you can maintain a conversation but would struggle to sing. At this effort level, your body primarily relies on fat oxidation for fuel, with Type I (slow-twitch) muscle fibers driving it. The physiological adaptations that occur during consistent Zone 2 training are substantial. Here are several key mechanisms:

Mitochondrial density can increase by up to 50% with consistent Zone 2 work
Capillary density around working muscles improves to allow better oxygen delivery
Stroke volume increases as the heart becomes a stronger pump, and blood plasma volume expands over time

All of these contribute directly to a higher VO2 max. Three to six hours of Zone 2 work per week is effective for most recreational athletes, while competitive athletes benefit from six to ten or more hours per week. For a Hyrox athlete balancing running with station-specific strength work, three to four hours of dedicated Zone 2 running per week is a realistic and effective target.

Facilities like BOD in Los Angeles offer VO2 max testing alongside DEXA body composition scans, giving athletes a data-driven starting point for personalised training zones rather than relying on generic heart rate calculations. When your zones are dialled in using actual gas-exchange data, every training session becomes more targeted and productive.

High-Intensity Intervals: The Direct Path to a Higher VO2 Max

If Zone 2 training builds the aerobic foundation, high-intensity interval training is the tool that raises the roof.

The Most Effective Interval Protocols for Hyrox Athletes

Not all interval sessions are created equal, and the protocol you choose should reflect where you are in your training cycle and what limiter you're targeting:

4×4 Minutes at 90–95% Max Heart Rate — The Norwegian protocol remains one of the most well-validated approaches. Four minutes of hard effort followed by three minutes of active recovery, repeated four times. This protocol specifically targets the VO2 max zone and has produced some of the most consistent improvements in the literature. For Hyrox athletes, performing these on a treadmill at a slight incline simulates the sustained running effort required during race segments.
30/30s and 15/15s — Shorter intervals of 15 to 30 seconds at very high intensity, followed by equal rest periods, accumulate significant time at or near VO2 max without the same psychological burden as longer intervals. The 15/15 protocol produced a 5.5% VO2 max improvement. These work well as a secondary interval session during the week and can be adapted for SkiErg or rowing to build sport-specific fitness.
Threshold Intervals (Tempo Work) — While not directly targeting VO2 max, running at or slightly below lactate threshold for sustained periods of 10 to 20 minutes pushes the threshold closer to your VO2 max ceiling. For Hyrox athletes, this intensity mimics the sustained moderate-to-hard effort required between stations and is critical for race-day performance.

A practical weekly structure for a Hyrox athlete in a general preparation phase might look like this: two to three Zone 2 runs (45–75 minutes each), one VO2 max interval session (such as 4×4 minutes), one threshold or tempo session, and two to three strength and station-specific sessions. The total running volume will depend on your experience and injury history, but 30 to 50 km per week is a reasonable range for athletes targeting a competitive open-category time.

Hard sessions need to be genuinely hard, and easy sessions need to be genuinely easy. There are greater improvements in peak power output and lactate threshold than those following a threshold-based model, precisely because the easy days allowed full recovery for the hard days to deliver their maximum stimulus.

Beyond the Workouts: Recovery, Nutrition, and Sleep

Sleep as a Performance Variable

Inadequate sleep impairs recovery, reduces training adaptations, and limits the body's ability to improve oxygen utilisation. Deep sleep is when growth hormone release peaks, driving muscle repair and cardiovascular adaptation. Seven to nine hours per night is the research-backed target, and for athletes in heavy training blocks, erring toward nine hours is a strategy.

Nutrition for Aerobic Adaptation

Two nutritional factors deserve specific attention for VO2 max development. First, iron status: iron deficiency is one of the most common and most overlooked limiters of endurance performance because it directly reduces the blood's oxygen-carrying capacity. Haemoglobin requires iron to bind oxygen, and even subclinical deficiency, ferritin levels that are "normal" but low, can meaningfully impair VO2 max. Athletes training at high volume, particularly female athletes and those on plant-based diets, should have ferritin levels tested regularly.

Second, post-training fuelling: consuming adequate carbohydrate and protein after intense sessions accelerates glycogen replenishment and initiates muscle protein synthesis. The goal is to support the recovery process so that the next training session can be performed at full quality. Underfuelling is one of the fastest ways to stall aerobic development.

Overtraining

A common pattern among motivated Hyrox athletes is adding more training volume when progress stalls, rather than improving recovery. Overtraining leads to burnout, hormonal disruption, and paradoxically, a decline in VO2 max. If your VO2 max has plateaued despite consistent training, the answer may be to do less rather than more, or at least shift the distribution toward more easy work and fewer moderate-intensity sessions.

Tracking Your Progress: Lab Testing vs. Wearable Estimates

Knowing your VO2 max is useful. Knowing it accurately is what makes it actionable. Most modern fitness watches provide VO2 max estimates using algorithms that correlate heart rate data with pace or power output. Estimates are useful for tracking trends over time. If your watch shows your VO2 max climbing from 42 to 46 over three months, your aerobic fitness is very likely improving. But for setting precise training zones, identifying specific limiters, and making programming decisions, a lab-based test using a metabolic cart provides the accuracy you need. The test involves graded exercise on a treadmill or bike while respiratory equipment analyzes each breath, measuring the exact point at which your body reaches its oxygen consumption ceiling. Typical costs range from $150 to $250, and when paired with body composition analysis, it gives athletes a comprehensive snapshot of where they stand and what to prioritise.

A Realistic Timeline: When Will Your VO2 Max Actually Improve?

Setting realistic expectations matters because VO2 max improvement is not linear, and it's not unlimited. If you're currently inactive or undertrained, noticeable improvements typically appear within four to six weeks of consistent training. The largest gains come early. Previously sedentary individuals may see increases of 15–20% in the first few months.

For already-trained athletes, improvements are smaller and slower: 3–7% over an eight- to twelve-week focused training block is a realistic target, according to the meta-analyses discussed earlier. VO2 max also has a genetic ceiling. Roughly 50% of VO2 max variation is heritable. It means that once you've maximised your genetic potential, further performance gains come from improving efficiency, threshold, and sport-specific skills rather than chasing a higher VO2 max number. Age is also a factor. VO2 max naturally declines approximately 10% per decade after age 25. However, VO2 max remains highly trainable at ages 40, 60, and even 80. The decline is a slope that consistent training can dramatically flatten.

Get tested, whether through a facility like BOD or another sports science lab, a baseline VO2 max test and metabolic assessment replace guesswork with data. You'll know your exact thresholds, your current VO2 max, and which energy systems need the most attention. Retest every 12 to 16 weeks to measure progress and adjust your programming. Protect your recovery with the same discipline you bring to your training. Sleep seven to nine hours. Eat enough to support adaptation. Monitor your iron levels. Resist the urge to fill every rest day with an "active recovery" session that's really just another moderate workout.

The athletes who improve fastest are the ones who train the smartest, with the right intensity at the right time, backed by data they can trust, and the discipline to let their bodies adapt between sessions. Your VO2 max is trainable. How much it improves depends on how strategically you pursue it.