I’m training for a HYROX race and want to become a faster runner. So I should probably just start running faster in training. 

It’s a logical way of thinking. To improve your speed during each of the eight one-kilometer runs in a HYROX race, you need to spend more time running faster. But in reality, it isn’t that simple, and oftentimes the opposite is true: The best way to become a faster runner is actually to spend more time running slower. 

“Most people assume that getting faster requires producing more energy, but becoming a better runner also means requiring less energy to run at the same speed. That is running economy,” explained long-time endurance coach and the founder of Aerobic Capacity, Chris Hinshaw, whose company offers HYROX training programs. 

He added: “Two athletes can run side-by-side at the same pace, but the more economical athlete uses less oxygen and energy to maintain it. That athlete is paying a lower physiological cost and has more capacity available when the race becomes difficult.”  

And ultimately, this comes down to having a larger aerobic base, which largely happens through Zone 2, and to some degree Zone 1, training. 

What is Zone 2 Training? 

Zone 2 is one of the training zones in the five-zone training model, which essentially divides training into five progressively more intense levels based on power output, Zone 1 being the least intense, Zone 5 the most. 

If you’re into physiological definitions, exercise physiologist Gommaar D’Hulst, the founder of WOD Science and the senior scientist at ETH Zurich in Switzerland, provided this definition of Zone 2 training: “The highest exercise intensity at which mitochondrial oxidative phosphorylation can match cytosolic glycolytic flux without requiring sustained net lactate accumulation.” 

OK, to help you out, in layman's terms, what this means is that the moment lactate begins building up in your body, you’re no longer in Zone 2 and you have effectively moved into Zone 3. 

Here’s a quick easy-to-understand explanation of what each zone of training looks like in Hinshaw’s words.  

• Zone 1: Recovery: ”Zone 1 is very easy work. Breathing is relaxed, metabolic disruption is minimal, and the goal is recovery plus low-cost movement.” 

• Zone 2: Aerobic Development: ”Zone 2 is controlled work. It improves mitochondrial function, capillary density, fat oxidation, and the ability to sustain a given pace with less physiological strain.” 

• Zone 3: Tempo: ”Zone 3 develops sustained tempo and durability. It creates more fatigue than Zone 2 and should not become the default intensity for every conditioning session.” (but for many, it does). 

• Zone 4: Threshold: ”Zone 4 is hard, controlled work. It develops the fastest pace an athlete can sustain without rapidly losing metabolic control, which makes it valuable for race pace and running under fatigue." 

• Zone 5: VO2 max: ”Zone 5 is severe-intensity work near the athlete's aerobic ceiling. It develops VO2 max, high-end speed, and repeatability, but the fatigue cost is high, so the weekly dose should remain limited.” 

That being said, determining which zone you’re running in isn’t quite as black and white as the above suggests. That’s because, as Hinshaw explained, “the aerobic, glycolytic, and phosphates energy systems do not switch on and off as intensity changes.” Instead, they work together, and various muscle fibres get recruited progressively as your force, speed, duration and fatigue increases. 

“What does change across the zones is how much each system and fibre type contributes, which fuels become more important, and how quickly fatigue develops,” Hinshaw explained. 

How Does Zone 2 Make Me a Faster Runner for HYROX? 

As already mentioned, aerobic capacity is built through Zone 1 and Zone 2 training. In a nutshell, the bigger your capacity (aka your engine), the more durability you have to “support harder efforts in training and racing,” Hinshaw explained.  

In this sense, your aerobic capacity is like a base or a foundation of a house: It’s not the part of your house you’re showing off to your friends, but without it, you can’t exactly build the rest of the house. 

In terms of HYROX specifically, when an athlete has a larger aerobic capacity, they can run faster at the same perceived effort, recover quicker between stations, and resist slowing down across the eight one-kilometer runs, which is especially important during HYROX because, with the exception of the first run, all of the seven other runs start with some degree of fatigue that only becomes enhanced by the station you complete before the run.  

“Each station can disrupt breathing rhythm, posture, cadence, stride, and muscular coordination, and the athlete with the stronger aerobic system restores those qualities sooner and returns to goal pace at a lower cost. Over eight runs, those small advantages become significant,” Hinshaw said. 

He added: “Your aerobic base determines how much of your running speed survives the stations.” 

Could My “Easy” Running Still Be Too Hard? 

According to research D’Hulst conducted, the answer to this question is yes. 

A couple years ago, he and his team put some non-elite, lifestyle CrossFit athletes through some testing, where they were told to workout at a 3/10 rate of perceived exertion (RPE), meaning in Zone 2.  

What they discovered, however, was that, physiologically speaking, eight out of 10 of them were actually training in Zone 3 (as measured by the fact that their lactate levels rose almost immediately), even though they thought they were in Zone 2.  

Interestingly, the opposite can be true for elite endurance athletes. They're so fit when they're training in Zone 2 that they’re still producing a ton of power, which puts a lot of metabolic stress on their body, D’Hulst explained. As a result, many elite endurance athletes do a lot of Zone 1 training. Sometimes, as much as 80 to 90 percent of their training is done in Zone 1, because it puts less stress on the body and helps them recover more effectively. 

Ultimately what this means is that, if D’Hulst’s small study holds merit, these lifestyle fitness enthusiasts would certainly benefit from building a bigger aerobic base via true Zone 1 and Zone 2 training. 

Worth Noting: D’Hulst’s study is in line with what Hinshaw sees as the biggest mistake people make when training for HYORX, which he described as “allowing easy sessions to dirt into moderately hard work.” When this happens, “the athlete loses the recovery benefit of low intensity without producing the quality of a true high intensity session,” he explained.  

Hinshaw reiterated: ”Race intensity should not dictate everyday training intensity. Easy training builds the capacity that allows hard training to be performed well.” 

How Much Time Should I Spend in Zone 2 if I’m Training for HYROX? 

According to Hinshaw, those training for their first HYROX race should spend 70 to 80 percent of their weekly endurance specific training in Zone 1 (10-15 percent) and Zone 2 (60-65 percent), while the other 20 to 30 percent should be a mix of Zone 3, 4 and 5.  

For an athlete who does three endurance sessions per week, on top of their other strength training and station work, an example of their week might look like this:  

• 1 endurance training session dedicated entirely to Zone 2 

• 1 endurance training session that is Zone 2 dominant, but with a small amount of controlled faster work 

• 1 endurance training session that is at your threshold pace, or involves intervals or compromised running (running fatigues immediately after a high intensity effort). 

Further, Zone 1 might come in the form of warm-ups, cooldowns, or optional recovery sessions, Hinshaw added. 

The Big Picture 

Despite the importance of Zone 2 for building a bigger engine, Hinshaw is adamant that Zone 2 alone “is not a complete program.” 

Its role is to build aerobic capacity, while threshold training helps you develop a sustainable race speed, Zone 5 helps improve high-end aerobic power, and compromised running sessions teach athletes how to recover after stations.  And all of the above are needed for a complete HYROX program.  

That being said, a big part of the picture comes down to prioritizing Zone 2, because, as Hinshaw explained, “Zone 2 does not simply make an athlete better at running slowly. It reduces the physiological cost of running quickly.” 

In other words, slower running now means faster running later.  

Author Bio:

Emily Beers is a fitness writer and journalist who has been working in the industry since 2009. She also spent a decade-and-a-half as a personal trainer and CrossFit coach, and competed at the CrossFit Games twice with a team and once as an individual.