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| Credit: @welcome_to_the_mill / Instagram |
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| CrossFit methodology and CrossFit enthusiasts have long promoted high-intensity training as the gold standard. And with good reason. The science seems to support it. |
- “There’s quite a bit of research showing that high intensity training leads to faster improvements in VO2 max, especially in shorter time durations, compared to lower intensity, easy work,” explained Gommaar D’Hulst, the founder of WOD Science and the senior scientist at ETH Zurich in Switzerland
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| This is, of course, music to the CrossFit athlete’s ears, since they generally do more high-intensity, interval training (often called HIIT), while low-intensity, 60-minute Zone 2 workouts can be, well, boring and time-consuming. And for the lifestyle athlete who trains just one hour a day, five days a week, setting aside a 60-minute, low-intensity workout doesn’t seem necessary. |
| But is this really accurate? Is Zone 2 training really “a waste of time” for the average CrossFit or even HYROX enthusiast? |
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| Is Zone 2 a Waste of Time? (if you only train 5h/week) |
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Zone Training Explained
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| Before we dive into the questions above, let’s quickly explain what we mean by training in a specific zone for those unfamiliar with the term. |
| VO2 max, a key metric for measuring fitness, is the maximum rate of oxygen consumption during physical activity. In other words, the higher your VO2 max, the more efficient your body is at delivering oxygen to the muscles. |
- Zone 1: low intensity (1-2 rate of perceived exertion or “RPE”)
- Zone 2: low intensity (3-4 RPE)
- Zone 3: moderate intensity (5-6 RPE)
- Zone 4: high intensity (7-8 RPE)
- Zone 5: high/maximal intensity (9-10 RPE)
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| That being said, training in these zones is more than just how hard you think you’re working; they’re physiological states. |
- The scientific definition of Zone 2, for example, that D’Hulst likes the most is: “The highest exercise intensity at which mitochondrial oxidative phosphorylation can match cytosolic glycolytic flux without requiring sustained net lactate accumulation.”
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| In simple terms, when lactate starts to build up in your body, you’re no longer in Zone 2. This means that just because you feel like you might be in Zone 2, it doesn’t necessarily mean you are physiologically in Zone 2. You could actually be in Zone 3. |
Back to the Question
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| If I’m a five-day-a-week gym go-er, is it better to focus on Zone 3-5 and forget about Zone 2? |
| According to D’Hulst, maybe not. |
| In his recent YouTube video, he discussed the science suggesting that HIIT and sprint interval training (SIT) lead to greater VO2 max adaptations than lower-intensity, Zone 2, or endurance training. |
| When you take a surface look at the science, this seems to be the case, he explained. But when you dig deeper, there are some “nuances” we should consider before making such sweeping statements. |
| D’Hulst cited a 2024 Norwegian study that reviewed the scientific literature on how exercise influences mitochondrial and capillary growth in human skeletal muscle. The study examined hundreds of previous research projects on how different exercise intensities impact VO2 max and other fitness-related adaptations. |
- This large-scale study found that, yes, HIIT and SIT have a greater impact on positive fitness adaptations in the first few weeks of a fitness program, but after that, they begin to plateau.
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| Endurance and Zone 2 training, on the other hand, are the opposite. They take longer for adaptations to happen, but over time, the benefits from increasing overall training volume with Zone 2 training surpass what you get from HIIT and SIT alone. |
| In other words, training volume might just be the big winner long term, and it can be difficult to accumulate enough overall volume for continued gains if all you’re doing is high-intensity training. |
The Big Picture
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| If you are “a superhuman” or “a genetic freak” who can handle a significant amount of high-intensity volume training each week, you might be able to avoid the plateau and continue seeing positive adaptations in your VO2 max, as well as mitochondrial and capillary improvements, in the long term, D’Hulst said. |
- But for the average person, doing some Zone 2 training can be incredibly effective for accumulating enough total work to achieve long-term aerobic gains.
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| It not only promotes fitness, but also helps prevent overtraining and encourages better recovery so you can train hard again the next day. |
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