I’ve noticed that health advice seems to go through cycles. There are fad diets, fad exercise routines, and fad vitamins and supplements. It’s kind of like how fashion recycles too. Observing the popular rise of zone 2 training had me reflecting on how I should interpret this growing interest, when I see that popular consensus shifts frequently.
Today every longevity expert is preaching about the benefits of zone 2 training. To be honest, I don’t know much about zone 2 training, and haven’t read any studies about it. I’m writing this from the viewpoint of a lay person observing a trend. It’s not a commentary on the science of zone 2.
In short, zone 2 training is jogging (or walking, swimming, erging, cycling etc). Some sort of aerobic exercise performed at pace comfortable enough to hold a light conversation. There are 5 zones. Zone 1 is a casual stroll. Zone 5 is an all out sprint, with the intensities of zones 2-4 somewhere in between.
Zones are not determined by pace or work output, however. For example, everyone’s zone 2 is different. Zone 2 for me may be a 15 minute mile, while for an athlete it may be a 6 minute mile. This is because zone 2 is defined by the maximum work one can generate while maintaining steady and low lactate levels (i.e. < 2mmol/L). The thought is that healthier mitochondria, and thus healthier individuals, can produce more work before shifting to anaerobic metabolism.
More importantly, the claim is that engaging in more zone 2 exercise is the best way to train to improve health and live longer. Estimating the energy producing capacities of the mitochondria provides a mechanistic explanation for why maximizing zone 2 training specifically can reduce the risks of cardiometabolic disease like diabetes, hypertension; and dementia, and heart disease.
What I found interesting was that before zone 2 training started trending 2-3 years ago, the best type of exercise was thought to be high intensity interval training, or HIIT. High intensity interval training consists of short bursts of high intensity with periods of rest, which sounds like the exact opposite of the tenants of zone 2 training. I don’t know what the proposed logic was for why HIIT was superior though it probably had something to do with type 1 and 2 muscle fibers, and how engaging different muscle types improve mitochondrial function and allows you to control which types of fuel to burn i.e. carbs or fat.
Regardless, the point of this essay is not to say which exercise is better or offer criticism on the validity of zone 2. Rather I found the shift in culture interesting because the shift resembled more of a swinging pendulum, rather than a building up from a stable foundation of knowledge.
Health advice appears to be cyclical. The science of zone 2 training may be innovative and offer important insight into physiology. But the practical application of long and steady training sessions is old. In the 70’s jogging was a cultural phenomenon1. There are many more examples of health paradigms swinging back and forth from diametrically opposed concepts. The Atkins diet was once popular, soon replaced by variations of low (saturated) fat, high carb, low animal product diets. Same with the advice on the harms/benefits of alcohol, eggs, sugar, sunlight, coffee, etc.
This makes me think that zone 2 training will again fall out of fashion, while we cycle back to other things. Perhaps back to strength training or hill sprints. However, for the average American who is metabolically unhealthy and living a sedentary life, any physical activity is better. And what seems to get people to change behavior is a good story. Any story, whether it’s completely made up, sensationalized, exaggerated, hyped, or scientifically based; it doesn’t matter. Today, the story that works is the one that gives permission to take it easy during a work out dressed up in buzz words like mitochondria, lactate and longevity2. Perhaps when people are bored of longer jogging sessions, the story that allows short but intense work outs will prevail again.
https://en.wikipedia.org/wiki/Running_boom_of_the_1970s
Personally, I like the idea of zone 2 training though I don’t do it myself. I’m even convinced that it may live up to all it’s health claims. If Olympic athletes and Tour de France competitors focus on it, I can’t argue with that. I also think that aging and metabolic disease like insulin resistance starts with a defect in the mitochondria.
For most people, focusing on zone 2 or lactate levels or target heart rate may be counter productive. The main take away is that lower intensity exercise produces benefits, and tiring, high intensity work outs aren’t required, and may not even be superior. Permission to go slow may help people start who otherwise wouldn’t have.
Interesting reflections - had never considered how specific exercise recommendations have changed over time. Probably because I feel massive gratification whenever I simply inspire a single patient to do any exercise at all.
A book I hope to read someday is Haywire Heart by John Mandrola. I appreciate his ability to critically appraise research. He was recently in a Sensible Medicine podcast that featured a spirited debated about whether someone can exercise too much. But like you say, the shades of harm/benefit between the extremes of excess and absence of exercise are probably very difficult to accurately differentiate, unless a thoughtful RCT were designed. I enjoyed the episode, if you hadn’t come across it:
https://open.spotify.com/episode/0UfIHlHIWlAtrU4p6MLD3Z?si=6XgfnufwTna2ScIatFsq0Q
When COVID hit, I saw people that lived unheathly lifestyles were hit hard. After binging on the Huberman Lab Podcast, I was motivated to leave my sedentary lifestyle behind and begin zone 2 training, which for me consisted of a brisk walk up and down the hills in our neighborhood with dumbells. Along with dietary changes, I felt better and lost wieght. I'm a believer because it works for me. Now I'm figuring out a good resistance routine for this 64 year old body......