Tag: hiking

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Zone-2 cardio has been having its moment. That comes from a lot of sources, but unfortunately a big one is Peter Attia. I say “unfortunately,” because Attia seems to have a weird, compulsive sense that zone-2 cardio work needs to be, I don’t know, pure in some way, rather than just being enough to promote good metabolic health.

Attia suggests that you do your zone-2 work on a treadmill, stationary bike, or rowing machine, so you can be in control of your effort level at all times. Then you can just get into zone 2 and stay there for 45 minutes.

I think this is crazy, and not just because 45 minutes of steady-state activity on a treadmill or stationary bike would be excruciatingly boring.

I do my zone-2 cardio with a mixture of walking my dog, running, and occasional hikes. Walking the dog isn’t perfect, because the dog keeps stopping to get in her sniffies, and no doubt my heart rate drops out of zone 2. Running isn’t great, because my heart rate probably spends a lot of time in zone 3 or zone 4. A lot of it is zone-2—at least, I can talk while I run, which is one of the tests for zone-2. (I run very slowly.) The hikes are probably perfect zone-2 cardio, but are a big time commitment in a single day.

Attia suggests that you optimize your cardio workouts by getting 3 hours a week of zone-2 cardio, which can optionally be divided into 4 45-minute workouts. And I’m sure that’s fine. But I suspect that getting in a couple of runs a week, along with a good bit of dog walking, is going to check the zone-2 cardio box no problem.

My theory (and I am not an MD, nor even a PhD in exercise physiology, but still) is that this is fine. You don’t need to get 45 minutes of pure zone-2 cardio to be metabolically healthy.

As I see it, the test for whether you’re getting enough zone-2 cardio is whether or not you can engage in a moderate level of exercise for an extended period—a 3-hour hike, let’s say. If you’re metabolically healthy you can go on and on at a moderate pace, because you’re doing it almost entirely aerobically.

Me on the Ham's Bluff Lighthouse trail on St Croix

If you can do that, you’re getting enough zone-2 cardio, regardless of whether your sessions are 45 minutes long, and regardless of whether they add up to 3 hours a week. If you’re not metabolically healthy, even going at a moderate pace is going to push you into anaerobic metabolism, which will quickly become impossible to maintain.

It probably is true that you need to get in 3 hours a week if you’re going to be able to go on long, long hikes. But the idea that they need to be pure zone-2 sessions, rather than mixed sessions at all different levels of intensity, is just crazy.

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For much of my life I thought that the key to losing weight was just exercising more. Especially in the mid-1980s, when I lived in Utah and California, I’d get out for some long hikes in the mountains and deserts and think, “If I could just do this all the time, it would be easy to maintain a proper weight.” That turns out to be both true and false.

The fitness influencer types like to say things along the lines of “You can’t outrun your fork,” meaning that you simply can’t burn enough calories to get ahead of eating way too much. I knew that wasn’t completely true. Read about any long-distance endurance athlete (ultra-marathoner, Tour de France rider, etc.) and you’ll have a window into really extreme efforts to eat enough just to keep going, let alone enough to recover for the next day’s effort.

I also have a slightly more ordinary example. A couple of guys I knew tried to bicycle around Lake Superior and Lake Michigan, and had to abandon the effort halfway through, because their riding (100+ miles per day) burned so many calories (perhaps 5000 calories on top of their basal metabolic rate, so maybe 7500 calories per day total), they ran out of money for food.

It’s tough to eat 7500 calories per day even without the financial limit, so it seems like, if you have all day to do nothing but exercise, and the will to exercise hard for several hours a day, perhaps you could “outrun your fork.”

Recent research shows that this is not the case, except in the very short term. People who are very active all day, like hunter-gatherers (but also subsistence farmers, and laborers of other sorts), burn more calories than people who are sedentary all day, but only modestly more.

A recent study showed that among of Hadza people, activity was almost insignificant as a predictor of total energy expenditure. They were remarkably active, but their calorie consumption was pretty ordinary. The study suggests that body size is just about all that matters

In that study, average total energy expenditure among Hadza men was 2649 calories per day. The average is higher among western men, but only because their body size is greater. (Hadza men averaged 50.9 kg (112 lbs), while Western men averaged 81.0 kg (179 lbs). Differences in BMI are more stark, with Hadza men having a BMI averaging 20.3, while Western men’s BMIs averaged 25.6.)

The point here is that it seems like your biology is attuned to wanting to eat 2600 calories and wanting to burn 2600 calories. (Adjust for frame size. It seems the Hadza men averaged about 5′ 2″.) You can be sedentary, under-eat to match, and not gain weight, but it’s not in tune with what your body wants, so you’ll be hungry all the time, as well as having all the side-effects of under-movement.

You can also try to exercise enough to burn more than 2600 calories, but it seems that as soon as you go over that level, your body starts trying to compensate—turning down whatever is easy to turn down, such as your immune system, and muscle-building system.

That doesn’t happen immediately. If you go on a century ride you will burn the extra 5000 calories that simple arithmetic would suggest. That would probably continue if you went on a three-day bicycle tour. But pretty quickly—probably just in a week or so—less-essential body functions would ramp down (and of course fatigue would ramp up) bringing your total consumption back down toward 2600 calories.

You can see how this would work well for hunters. You go for a hunt one day (or two or three days), hiking or running for miles, finding prey, tracking it, and finally killing it. Then you (and your whole tribe) have lots of food to eat for a day (or two or three). During extended periods of excess activity maybe your immune system and muscle-building system ramps down, but then during periods of ample food and less activity, maybe it ramps up extra, allowing for full recovery.

Consuming more calories than you burn for more than a few days, however, quickly leads to problems. Increased fat storage is probably the least of them. Insulin resistance is another. Systemic inflammation is another. Those extra calories will go into the things that get turned down when you’re extra-active, such as the immune system. I don’t know that there’s any evidence, but an obvious possibility is that a lot of auto-immune disorders are just an immune system that never gets turned down because people are never active enough to burn more calories than they eat, if only for a day or two.

I think it’s true that you can’t out-exercise excess calorie consumption. However, you can definitely under-exercise—and trying to under-eat to match that will also cause problems. Humans evolved to thrive with an ideal level of activity.

It’s also true that you don’t need to hit that particular level of activity and food consumption every day. In fact, I’m sure you’d be better off to be moderately active most days, and then very active 1–3 days a week. My long-ago dream of being able to hike 10–15 miles every day and then eat all I want turns out to be a terrible idea. Rather, you want to walk 5 or 6 miles most days, and then hike 10–15 miles just once or twice a week. (Feel free to swap in bicycling or rowing or whatever you like for the long days of vigorous activity, although you probably want to keep in the basic walking if you possibly can.)