What type of exercise, and how much, is ideal?

Most chronic diseases that humans suffer from are mismatch diseases. Daniel Lieberman, a paleoanthropologist at Harvard University, uses this term to describe health conditions that result from our bodies not being adapted to our modern lifestyle and environment. It’s not old age that makes us sick—it’s things like processed food, smoking, toxins, and physical inactivity.

The effects of these lifestyle and environmental factors tend to build up over time, worsening our health as we age. So, it can be easy to blame our poor health on old age. But researchers who study hunter-gatherer tribes that still live a traditional subsistence lifestyle observe that tribe members rarely, if ever, suffer from chronic disease, and typically live very healthy lives until they eventually die quickly from respiratory or infectious diseases, violence, or accidents.

We know that our ancestors were more physically active than most of us are today—that’s why we’re told to exercise in order to maintain our health and make up for the fact that much of our day is spent doing sedentary activities.

But what type of physical activity and how much is ideal for human beings? These are the questions that Lieberman thoroughly answers in his latest book Exercised. A secondary question emerges in the book as well: If regular movement has always been part of our existence, why don’t we want to exercise?

How active were our ancestors?

Until the beginning of agriculture around 10,000 years ago, all humans were hunter-gatherers. And until about 80,000 years ago, all of our ancestors lived in Africa. So as Lieberman explains, to get a true understanding of what our level of physical activity was as we evolved, we need to study the hunter-gatherer tribes of Africa.

One of the tribes that has been studied the most is the Hadza tribe of Tanzania. When Hadza men go out on a hunt, they typically walk between seven and 10 miles, varying their pace and taking breaks when needed. Women are responsible for gathering food, which involves walking several miles away from camp (with infants and toddlers in tow) and spending a few hours digging for tubers and gathering berries, nuts, and other food. When the Hadza are at camp, they spend their time doing light chores while sitting on the ground, taking care of their children, and simply relaxing when they can.

Exercise as we know it—movement for the sake of burning calories, toning muscles, and improving health—is a foreign concept to hunter-gatherer tribes like the Hadza. Rather, their goal is to conserve energy as much as possible. Since they don’t grow or store large amounts of food, they only eat what they can find each day. When food is scarce, which it often is, they don’t waste energy on unnecessary physical exercise—their bodies need those calories to survive and reproduce.

A study in which Hadza adults wore heart rate monitors for several days found that the average Hadza adult spends two hours and 14 minutes per day doing moderate or vigorous activities, and three hours and 40 minutes per day doing light activities. Hadza women walk an average of five miles per day (equal to the American Heart Association’s recommendation of 10,000 steps), and the men walk between seven and 10 miles per day. Similarly, men of the Tarahumara tribe (of Born to Run fame) walk an average of 10 miles per day.

So while hunter-gatherers are certainly moving for a good part of their day, they are by no means running marathons on a regular basis or doing intense weightlifting workouts. They simply do the physical activities necessary for them to survive, and little else. Yet shockingly, their moderate activity level is six to 10 times greater than the average American or European adult.

How exercise as we know it came to be

Exercise for the sake of physical improvement is a behavior unique to humans, and a relatively new one at that. Early farmers had to work just as hard, if not harder, than hunter-gatherers. But in large settlements and cities, not everyone had to do the daily work of farming. Ancient texts and paintings from civilizations including Egypt, Mesopotamia, Greece, China, and India show the beginnings of exercise as we know it today: potential warriors took part in combat training, and spiritual philosophers encouraged people to train both their minds and their bodies.

During the Renaissance and through the 19th century, exercise became a part of everyday life for wealthy people. Since wealthy people didn’t have to toil in the fields, they had both time and energy for recreational physical pursuits. Gymnastics, fencing, and horseback riding all became popular endeavors for well-educated, affluent people.

During the 19th and 20th centuries, governments became worried when they noticed that lack of physical fitness in soldiers led to losses on the battlefield. And for the past 150 years or so, doctors and educators have consistently voiced their concerns that each generation is less physically fit and healthy than the previous generation.

For some of us today, all of our daily work is done on a computer, by moving only our arms and hands. We get food delivered with the click of a button. There isn’t much in our daily lives that we actually need to get up and do in order to survive.

It’s easy to see our desire to use technology to make our lives easier as a bad thing—it’s as if we want to be as lazy as possible. But we’re just doing what evolution trained us to do: survive by expending as little energy as possible. Thanks to our incredible capacity to learn and figure things out, humans have been developing tools and technology to make our lives easier for the past 2.6 million years! But now our lives are so easy that we barely have to lift a finger to survive, and that’s why exercise has become a necessary part of our lives. Technology has brought us to the point where doctors and the government must prescribe movement so that we don’t suffer from chronic diseases related to physical inactivity.

What our activity level is like today

The U.S. Government recommends that we get at least 150 minutes of moderate exercise per week, which equates to 21 minutes per day. This is just one-sixth as much moderate exercise as the Hadza tribe gets per day, and yet 50% of American adults and 75% of teenagers don’t meet this minimum activity level.

Part of our inactivity can be blamed on our jobs. Thanks to advances in technology, less than 20% of jobs today require moderate or vigorous levels of activity, down from 50% of jobs just 60 years ago.

Outside of work, we use energy-saving devices to carry out physical tasks we once did ourselves. In our free time, we’re entertained by screens rather than games and other activities involving movement.

If you work out regularly, you’re likely wondering: Does an hour or two at the gym erase the negative effects of sitting for the rest of the day? Sadly, large studies have shown that the answer is no. A 2015 study of 930 men found that independent of level of fitness, being sedentary for much of the day increases risk of metabolic syndrome (a group of conditions that occur together, increasing the risk of heart disease, stroke and type 2 diabetes).

A 2012 study of over 240,000 adults examined the risk of all-cause, cardiovascular, and cancer mortality as related to time each day spent being sedentary. The study found that people who were most sedentary (seven or more hours per day) had significantly higher risk of dying of all causes than those who were the least sedentary (one hour or less per day), independent of their level of physical fitness. Even among adults who exercised for an hour or more every day, risk of all-cause and cardiovascular death was 50% higher for those who were most sedentary compared to those who were least sedentary. This is why we see headlines that say “sitting is the new smoking.”

One explanation for why sitting is damaging to our health is inflammation. When we engage in moderate or vigorous exercise, our body first increases inflammation in order to prevent or repair damage caused by the exercise. In the process, our body repairs preexisting damage as well.

Soon after, our body reduces inflammation in order bring us back into homeostasis. This reduction in inflammation is typically larger than the initial increase, making the overall effect of exercise anti-inflammatory. This is why physically active people have lower levels of inflammation and oxidative stress. And a study of 4757 people found that among people who are sedentary for much of the day, those who get up frequently and move around have lower levels of inflammation than those who sit for long stretches of time. Simply getting up and moving around for a few minutes has the net effect of reducing inflammation.

So, while humans are adapted for moderate levels of physical activity rather than no exercise or extreme exercise, our modern definition of “moderate” is quite different than what it was just a few hundred years ago. And when we’re not doing physical tasks, we’re likely to be truly sedentary, as opposed to hunter-gatherers who sit and squat for short periods of time, often doing work with their hands.

Humans are built for endurance

We’ve learned how active our ancestors were, and how active we ought to be today in order to reduce our risk of death. But what type of exercise is best for us? All signs point to endurance.

This does not mean you need to run marathons in order to achieve optimal health—quite the opposite. Our ancestors walked five to 10 miles each day, typically at a moderate pace to avoid unnecessary energy expenditure. Five miles is roughly equivalent to 10,000 steps, so we ought to be getting between 10,000 and 20,000 steps per day (or an equivalent amount of endurance activity).

In addition to observations of how our ancestors lived, we have the physical evidence in our bodies to prove that we’re evolved for endurance. Unlike apes, we evolved to have long legs and springlike tendons in our legs that allow us to run long distances efficiently. And humans’ leg muscles are made up of 50% to 70% slow-twitch fibers, making us great at walking and running long distances slowly, as opposed to chimpanzees who have just 32% slow-twitch muscle fibers.

Most important is our ability to sweat. Unlike most animals that have sweat glands only on their paws, and monkeys and apes who have small numbers of sweat glands on other parts of their bodies, humans alone have several million sweat glands all over our bodies. These glands allow us to keep cool while walking or running continuously, even in hot weather—something that no other animal can do. As Lieberman says, “Humans are the sweating champions of the animal world.”

If walking and running don’t appeal to you, consider dancing. Dancing is a part of daily life in all non-industrial cultures, an essential element of spiritual rituals, celebrations, healing, and bringing luck. Hunter-gatherer tribes dance for hours, sometimes all night, on a regular basis. Just like walking and running, dancing builds stamina, strength, and coordination, and releases mood-boosting brain chemicals that give you a natural high.

Weight-lifting fans might be wondering: What about muscle and strength? Weren’t prehistoric men big and muscley? Not really. When food was scarce, having too much muscle was a liability because it took more calories to maintain that muscle mass. Our ancestors only wanted as much muscle as was needed to carry out their daily activities effectively.

How exercise helps prevent chronic disease

Lieberman concludes his book with a detailed section describing why regular moderate exercise is critical in preventing many common chronic diseases that we associate with aging. He points out that middle-aged and older hunter-gatherers never get to relax and retire. They remain active members of their tribe throughout their lives, participating in hunting and gathering food, doing tasks at camp, and helping with childcare.

In fact, many older tribe members are more active than their young adult children who are busy taking care of infants and toddlers. The average 65-year-old hunter-gatherer man has better aerobic capacity than the average 45-year-old American man.

One reason why exercise helps to prevent chronic disease is that exercise strengthens the immune system. This helps to prevent cancer as well as viral and bacterial infections. Research has clearly shown that moderate exercise, rather than no exercise or extreme exercise, is very effective at improving immunity.

Regular activity also helps to prevent chronic musculoskeletal conditions including osteoarthritis, osteoporosis, and sarcopenia. The more we use our muscles and bones, the stronger they stay throughout our lives, reducing the risk of osteoporosis and sarcopenia; as they say, use it or lose it.

And rates of osteoarthritis have risen dramatically since we’ve become more sedentary. Lieberman educates us that osteoarthritis is not caused by wear and tear as is commonly thought—it’s actually caused by inflammation that eats away at the cartilage in our joints. In many cases, this inflammation is caused by obesity and physical inactivity.

Exercise helps to prevent Alzheimer’s disease and other neurodegenerative diseases by stimulating the production of a protein called brain-derived neurotrophic factor (BDNF). BDNF was first produced by the brain to give mammals energy during physical activity. As we evolved, it also took on the role of being “Miracle-Gro” for the brain: encouraging the growth of new neurons, improving neuron function, preventing premature neuron death, and improving signal strength between neurons. Physical activity is the only way we can produce high levels of BDNF, so exercise is critical for preserving brain function as we age.

Regular exercise has proven to be as effective as pharmaceuticals and therapy for mental health conditions, which affect about one in five American adults. As I’ll describe in the next section, exercise increases levels of dopamine, serotonin, endorphins, and endocannabinoids, all of which make us feel happy and reduce our stress. Exercise stimulates the release of the neurotransmitters norepinephrine, glutamate, and GABA, which are often low in people who have depression and anxiety. Exercise also reduces levels of the stress hormone cortisol and improves sleep quality.

Cardiovascular disease, including high blood pressure and coronary artery disease, is clearly a mismatch disease. Researchers have found that hunter-gatherers in their 80s have the same low blood pressure as those in their 20s. Rates of hypertension and coronary artery disease only start to go up when populations become industrialized; that’s when levels of cholesterol and inflammation rise to unhealthy levels, leading to cardiovascular disease. Physical inactivity is a factor in this, as is obesity, poor diets, smoking, and stress.

While obesity is much more a result of diet than lack of exercise, physical inactivity does play a role. Experts agree that the overeating of high-calorie processed foods is the main factor in developing obesity. Thus, the most efficient way to lose weight is to eat only whole, unprocessed foods, and an appropriate amount of calories each day. If you use only exercise to lose weight, your results will be far more gradual. However, studies show that among people who have successfully lost weight, those who exercise regularly are much less likely to regain the weight.

Diet and exercise are both important in reversing metabolic syndrome (high blood sugar, high cholesterol, high blood pressure, and large waist circumference) and type 2 diabetes. These are two conditions which are clearly mismatch diseases, as they’re unheard of among hunter-gatherers and have only recently reached epidemic levels. Approximately 20% to 25% of the world’s adults have metabolic syndrome, and type 2 diabetes is now the fastest growing chronic disease in the world. Being overweight, eating a poor diet, and being sedentary are the main contributors. While drugs are often prescribed to manage these conditions, diet and exercise can reverse them permanently, and often quickly.

Lieberman notes that regular moderate cardiovascular workouts are the most effective type of exercise for prevention of most chronic diseases. An exception is metabolic syndrome and type 2 diabetes, which research show can benefit from a combination of cardio, high-intensity interval training, and strength training.

Why don’t we WANT to exercise?

Are humans naturally averse to exercise? In some respects, yes. While our bodies evolved to function best with regular physical activity, our minds evolved to only move when necessary or pleasurable, and to conserve energy whenever possible. Our instinct to avoid moving, combined with the fact that most of us don’t need to move much anymore, is a big problem.

One of the main reasons people report for not working out is lack of time. Yet the average person spends roughly three hours per day watching television. Most of us have no problem making time for things we enjoy doing. Avid exercisers often look forward to their workouts because exercise feels so good to them, both during and after their workout. They may wonder, why doesn’t everyone work out? It feels so good! Lieberman explains why:

  • Dopamine is a feel-good chemical secreted by the reward system in our brain that makes certain things feel good, like food, sex, and exercise. But dopamine levels only go up when we exercise—they don’t help us get motivated to start our workout. In addition, dopamine receptors are less active in people who aren’t physically active on a regular basis, and people who are obese have fewer active dopamine receptors.

  • Serotonin is a neurotransmitter that helps us feel pleasure, control impulses, and sleep better, among other things. Exercise elevates levels of serotonin, which is why exercise is just as effective as prescription medication for depression. But people who aren’t physically active may have lower serotonin activity, making it difficult for them to get the motivation to exercise in the first place—a vicious cycle.

  • Endorphins are our bodies’ natural opioids, alleviating pain and making exercise more comfortable. Endorphins may play a role in exercise addiction, and their effects can last for hours after a workout. But it takes 20 minutes or more of intense exercise before we start producing endorphins, so people who do short, less intense workouts may never even reach the point where endorphins are produced.

  • Endocannabinoids are our bodies’ natural version of the active ingredient in marijuana. While we used to think that endorphins were responsible for “runner’s high,” recent research using opioid blockers shows that endocannabinoids play a much bigger role in attaining that relaxed, happy, zen feeling you get after a long bout of intense exercise. Not much research on endocannabinoids and exercise has been done yet, but scientists suggest that at least 30 minutes of moderate to intense exercise, at 70% to 80% of max heart rate, is likely needed to trigger the release of the mood-enhancing chemicals.

If you want to start feeling good during and after your workouts, you will have to go through a period of time in which your brain and body adapt to being more physically active. Gradually, you’ll start feeling the mood-enhancing, stress-reducing effects of dopamine, serotonin, endorphins, and endocannabinoids.

Until exercise starts feeling good—and even afterward—Lieberman has some suggestions on how to make exercise a part of your daily life:

  • Make exercise a social activity, either with a friend, a trainer, or a group class

  • Entertain yourself with music, podcasts, or television while you work out

  • Exercise outdoors in a beautiful place

  • Do fun workouts like dancing or playing sports

  • If you tend to get bored doing the same activity, keep changing up your routine and try different types of workouts

  • Reward yourself for working out

  • Find a way to socially commit to regular exercise, like scheduling workouts with a friend or trainer

  • Make exercise a non-negotiable part of your regular routine, and make it easy (lay out your workout clothes the night before, and join a gym that’s on your way to work)

What’s the right formula?

While research clearly shows that humans thrive on lots of moderate cardiovascular exercise, it can be tough to ignore the hype of HIIT (high-intensity interval training) workouts and the allure of big, strong muscles attained by lifting heavy weights. And, research does show the benefits of HIIT and strength training. So, what’s the right formula? Is there an amount of each type of exercise that we should strive to incorporate into our daily lives?

Let’s look again to hunter-gatherers for our answer. We know they walked five to 10 miles per day, so we can aim to incorporate the equivalent of that much moderate cardio into our routine. Did they do high-intensity interval training? They undoubtedly did, but likely only when needed—like to run or fight for their lives. We don’t know how often this was, and it certainly varied. Most experts currently recommend doing short HIIT workouts two to three times per week. If you’re not interested in going to a new class or starting a new type of workout, an easy way to incorporate HIIT into your routine is to simply amp up the intensity of your current workout for a short period of time after you’re warmed up. For example, I do a series of short sprints at the end of my long runs a few times per week.

As for strength training, we know that our hunter-gatherer ancestors didn’t want excessively large muscles because it took too many calories to maintain them. Their strength training consisted of their daily activities, which they did as efficiently as possible. They didn’t do a lot of repetitions with the goal of building muscle—they would have thought we’re crazy for doing such a thing. Instead, they likely carried out their tasks in as few repetitions as possible, an approach similar to that of MSTF (Mindful Strength Training to Failure), outlined in Deep Fitness (a book I highly recommend). This style of strength training only needs to be practiced one to two times per week, for a total of 30 minutes per week, so it’s an easy addition to your workout routine—and may even save you some time, if you currently spend a lot of time strength-training.