Introduction
In "Exercised," Daniel Lieberman, a Harvard professor of evolutionary biology, takes a fresh look at exercise through the lens of human evolution. This book challenges many common assumptions about physical activity and offers a new perspective on why exercise is both difficult and essential for modern humans.
Lieberman's approach combines insights from anthropology, evolutionary biology, and modern scientific research to explore how our bodies evolved and why exercise is so important for our health. He tackles common myths and misconceptions about sleep, strength, and fitness, providing readers with a more nuanced understanding of human physiology and the role of physical activity in our lives.
The book's central argument is that while humans evolved to be physically active, we didn't evolve to exercise in the way we think of it today. This insight helps explain why many people struggle to maintain regular exercise habits and offers clues for how we can make physical activity more appealing and sustainable.
We Didn't Evolve to Exercise
One of the most surprising and counterintuitive ideas in "Exercised" is that humans didn't evolve to exercise in the way we typically think about it today. Lieberman argues that this insight is crucial for understanding our complicated relationship with physical activity.
When we imagine our early human ancestors, we often picture them as constantly active – hunting, gathering, and navigating challenging environments. While it's true that our predecessors were generally more physically active than modern humans, Lieberman points out that there's a crucial difference between necessary physical activity and exercise as we know it today.
For our ancestors, physical activity was an unavoidable part of survival. They had to move to find food, escape predators, and perform other essential tasks. In contrast, exercise as we define it now is voluntary physical activity, usually undertaken to improve health and fitness. This distinction is key to understanding why many people find it challenging to stick to an exercise routine.
Lieberman explains that evolution didn't give us an innate drive to exercise. Instead, we evolved to be active when necessary and to conserve energy when possible. This makes perfect sense from an evolutionary perspective. In environments where food was often scarce, wasting energy on unnecessary activity could be dangerous. Any extra calories burned through voluntary exercise would deplete energy reserves needed for survival and reproduction.
This insight helps explain why forcing ourselves to exercise often feels like a struggle. We're essentially fighting against our evolutionary programming, which tells us to save energy whenever possible. It's not that we're lazy; rather, we're behaving in a way that would have been adaptive for most of human history.
However, Lieberman is quick to point out that this doesn't mean we should give up on exercise. On the contrary, understanding why exercise can feel challenging can help us approach it with more compassion and develop better strategies for incorporating physical activity into our lives. Instead of shaming ourselves or others for reluctance to exercise, we can recognize that overcoming these instincts requires effort and dedication.
The Myth of Eight Hours' Sleep
Another common belief that Lieberman challenges is the idea that everyone needs eight hours of sleep per night. This notion is so ingrained in our culture that many people feel anxious or guilty if they don't achieve this supposedly ideal amount of sleep. However, Lieberman argues that the evidence doesn't support this one-size-fits-all approach to sleep.
The origin of the eight-hour sleep recommendation is somewhat murky. Lieberman traces it back to the 19th century when labor activists used the slogan "Eight hours for work, eight hours for rest, eight hours for what we will!" While this was an effective rallying cry for better working conditions, it wasn't based on scientific research about optimal sleep duration.
Recent research has shed new light on human sleep patterns, particularly studies of hunter-gatherer and subsistence farming communities. Contrary to the popular belief that pre-industrial humans slept more than we do today, these studies have found that such populations actually sleep less on average than people in industrialized societies.
For example, research conducted by Jerome Siegel and his colleagues at UCLA examined the sleep habits of hunter-gatherer groups in Tanzania, the Amazon rainforest, and the Kalahari desert. They found that these populations averaged about six and a half hours of sleep per night, with slight seasonal variations. Similar studies of Amish farmers, rural Haitians, and subsistence farmers in Madagascar have yielded comparable results.
These findings suggest that it's entirely normal and potentially even optimal for many people to sleep less than eight hours per night. In fact, some studies have indicated that people who sleep around seven hours tend to have better health outcomes than those who sleep either more or less.
Lieberman emphasizes that sleep needs can vary significantly between individuals and even for the same person under different circumstances. Factors such as age, activity level, overall health, and even the time of year can all influence how much sleep a person needs.
This doesn't mean that sleep isn't important – it absolutely is. But Lieberman argues that we should be more flexible in our approach to sleep and pay attention to how we feel and function rather than rigidly adhering to an arbitrary eight-hour rule. If you consistently feel well-rested and alert with seven hours of sleep, there's likely no need to force yourself to stay in bed longer.
Interestingly, Lieberman notes that one of the best ways to improve sleep quality is through regular exercise. Physical activity during the day can help regulate our circadian rhythms and promote deeper, more restorative sleep at night. This connection between exercise and sleep quality underscores the interconnected nature of various aspects of human health and well-being.
The Myth of Natural Brawniness
Another common misconception that Lieberman addresses is the idea that our hunter-gatherer ancestors were naturally muscular and brawny. This belief is often promoted by proponents of "primal" or "paleo" fitness regimens, who argue that modern humans should strive to emulate the physiques of our prehistoric forebears.
However, Lieberman points out that this image of universally muscular early humans doesn't align with what we observe in contemporary hunter-gatherer populations. While these groups are generally fit and lean due to their active lifestyles, they're not typically exceptionally muscular by modern standards.
For example, studies of the Hadza people in Tanzania, one of the last remaining hunter-gatherer societies, show that their strength levels are moderate and fall within the normal range for Western populations. Their grip strength and overall upper-body strength are comparable to average Westerners and actually lower than those of trained athletes.
Similar observations have been made of other hunter-gatherer groups, such as the Mbuti of central Africa, the Batek of Malaysia, and the Aché of Paraguay. While these populations are generally fitter than the average person in industrialized societies, their muscle size and strength are not extraordinary.
Lieberman offers several explanations for why humans didn't evolve to be naturally brawny:
Limited resistance training: Without modern gym equipment, it's challenging to progressively increase muscle size and strength beyond a certain point. Body-weight exercises can improve fitness, but they have limitations in terms of building significant muscle mass.
Caloric costs: Maintaining large muscles requires a lot of energy. On average, about 20% of our energy intake goes towards muscular maintenance. Increasing muscle mass would increase this energy demand, which could be disadvantageous in environments where food was often scarce.
Evolutionary trade-offs: While being very strong might have some advantages (like fighting off predators or attracting mates), these benefits weren't significant enough to outweigh the costs of maintaining extra muscle mass. Evolution favored a balance that allowed humans to be strong enough for daily tasks without expending excessive energy on muscle maintenance.
This doesn't mean that building muscle is bad or unnatural. In our modern environment, where food is plentiful and we often lack physical challenges, strength training can have numerous health benefits. However, Lieberman's point is that we shouldn't assume that being extremely muscular is our natural state or that everyone should strive for a bodybuilder physique.
Instead, he suggests that we evolved to be strong enough to handle the physical challenges of daily life in our ancestral environments. This level of fitness is still beneficial today, even if our daily challenges look different. Regular strength training can help maintain muscle mass, improve bone density, and enhance overall health, but it's not necessary or natural to strive for extreme muscularity.
The Role of Walking in Weight Loss
The question of whether walking can effectively contribute to weight loss is a contentious one in the field of exercise science. Lieberman delves into this debate, offering a nuanced perspective based on both evolutionary insights and modern research.
Traditionally, the argument for walking as a weight-loss tool was straightforward: walking burns calories, and if you burn more calories than you consume, you'll lose weight. However, some researchers have argued that walking is an inefficient method for weight loss because it burns relatively few calories and can increase appetite, potentially leading to compensatory eating.
Lieberman acknowledges that walking alone, especially in small amounts, is unlikely to lead to significant weight loss. He cites a study where overweight and unfit individuals were instructed to walk briskly for 150 minutes per week without changing their diets. The results showed almost no weight loss, which seems to support the skeptics' view.
However, Lieberman argues that walking can still play an important role in weight management when done in sufficient quantities and combined with other strategies. He points to the same study, which also included a group that walked for 300 minutes per week. This group showed more encouraging results, losing an average of six pounds over twelve weeks. While this might not seem dramatic, sustained over a year, it could potentially lead to significant weight loss.
More importantly, Lieberman emphasizes the role of walking in maintaining weight loss. Research shows that people who lose weight through diet alone often regain a significant portion of that weight within a year. However, those who combine weight loss with regular exercise, including walking, are much more likely to maintain their new weight over time.
Lieberman explains that humans evolved to be efficient walkers, which is generally a good thing but can make it challenging to use walking as a primary weight-loss tool. Our bodies are so well-adapted to walking that we expend relatively little energy doing it, especially compared to other forms of exercise.
Despite this, walking offers several advantages for weight management:
Accessibility: Walking requires no special equipment or skills, making it an exercise option available to almost everyone.
Low impact: Unlike more intense forms of exercise, walking is gentle on the joints, allowing for frequent, consistent activity.
Sustainability: Because walking is low-intensity, it's easier to maintain as a long-term habit compared to more strenuous forms of exercise.
Additional health benefits: Regular walking can improve cardiovascular health, reduce stress, and provide other health benefits beyond weight management.
Lieberman suggests that for optimal results, walking should be combined with other strategies such as dietary changes and more intense forms of exercise. He also notes that the amount of walking matters – while a short stroll might not have a significant impact on weight, longer or more frequent walks can make a difference.
In essence, while walking isn't a miracle solution for weight loss, it can be an valuable component of a comprehensive approach to weight management and overall health. Its effectiveness lies not just in the immediate calorie burn, but in its ability to support long-term health and fitness habits.
Debunking Running Injury Myths
Running is a popular form of exercise, but it's also surrounded by many myths and misconceptions, particularly regarding injuries. Lieberman tackles these concerns head-on, offering a more balanced perspective on the risks and benefits of running.
One common belief is that running inevitably leads to injuries, especially to the knees and joints. Many people avoid running altogether due to fears of wear and tear on their bodies. However, Lieberman argues that these fears are largely unfounded and that running, when done properly, doesn't have to result in frequent injuries.
Research suggests that running injury rates follow a U-shaped curve. Novice runners and very serious, high-mileage runners are at the highest risk of injury, while moderate runners in between these extremes experience relatively few problems. This pattern challenges the notion that more running always equals more injuries.
Contrary to popular belief, studies have shown that running and other forms of physical activity actually promote healthy cartilage rather than wearing it down. Regular runners are not at higher risk for osteoarthritis compared to non-runners. In fact, some research suggests that runners may have a lower risk of osteoarthritis than sedentary individuals.
However, Lieberman doesn't deny that running injuries can and do occur. The key to preventing injuries, he argues, lies in allowing the body time to adapt. Many novice runners make the mistake of increasing their mileage or speed too quickly, which doesn't give their bodies sufficient time to adjust to the new stresses. Lieberman recommends following the "10 percent rule" – not increasing weekly mileage by more than 10 percent – to reduce injury risk.
To illustrate the body's remarkable ability to adapt to running, Lieberman shares an anecdote from his own research. In 2015, he followed a group of eight runners who ran across the United States, covering 3,080 miles in about six months. At the start of their journey, these runners experienced significant pain and stiffness. However, as time went on, their bodies adapted. Of the fifty injuries reported during the run, about 75 percent occurred in the first month. By the final month, no injuries were reported at all.
This example demonstrates that the human body can adapt to handle impressive amounts of running, given sufficient time and gradual progression. It challenges the notion that running is inherently damaging to the body.
Lieberman also discusses the importance of proper running form and appropriate footwear. While he doesn't advocate for any particular style of running or type of shoe, he emphasizes the need for runners to listen to their bodies and find what works best for them individually.
Some key takeaways for injury prevention in running include:
- Gradual progression: Increase mileage and intensity slowly to allow for adaptation.
- Proper rest and recovery: Allow time between runs for the body to repair and strengthen.
- Cross-training: Incorporate other forms of exercise to build overall fitness and reduce repetitive stress.
- Attention to form: Focus on maintaining good posture and avoiding overstriding.
- Appropriate footwear: Choose shoes that are comfortable and suit your individual running style.
By debunking these myths about running injuries, Lieberman encourages more people to consider running as a viable form of exercise. He emphasizes that the health benefits of running – including improved cardiovascular health, stronger bones, and better mental health – far outweigh the potential risks for most people.
The Importance of Staying Active as We Age
One of the most crucial messages in "Exercised" is the importance of maintaining physical activity throughout our lives, especially as we age. Lieberman contrasts the typical aging process in industrialized societies with that of hunter-gatherer populations to illustrate how staying active can dramatically impact health and longevity.
In many industrialized countries, it's common for physical activity levels to decline significantly with age. For example, Americans in their seventies typically walk about half as much as they did in their forties. This reduction in activity is often accompanied by a host of health problems commonly associated with aging, such as cardiovascular disease, type 2 diabetes, and cognitive decline.
However, Lieberman argues that many of these "diseases of aging" are not inevitable consequences of getting older. He points to hunter-gatherer societies, such as the Hadza in Tanzania, where older individuals maintain high levels of physical activity well into their later years. As a result, these populations experience a much more gradual decline in fitness and rarely suffer from the chronic diseases that plague many older adults in industrialized societies.
Interestingly, hunter-gatherers often have life expectancies comparable to those in developed countries, despite lacking access to modern medical care. Those who survive infancy typically live to be between 68 and 78 years old, not far off from life expectancy in the United States. The key difference is in the quality of life in those later years.
Lieberman introduces the concept of "compression of morbidity" to explain this phenomenon. In hunter-gatherer societies, the period of physical decline and ill health (morbidity) is compressed into a relatively short period at the end of life. In contrast, many people in industrialized societies experience extended periods of poor health and disability in their later years.
To support this idea, Lieberman cites the Stanford Runners Study, conducted by medical professor James Fries. This long-term study followed 500 runners and 400 non-runners, all over 50 years old, for many years. The results were striking:
Longevity: By the end of the study, non-runners were about three times more likely to die in a given year compared to runners.
Physical capability: Non-runners lost the ability to perform basic tasks (like walking, dressing, and other routine activities) at twice the rate of runners.
Quality of life: Runners not only lived longer but maintained their independence and quality of life for a greater portion of their lives.
These findings underscore the profound impact that staying physically active can have on the aging process. Regular exercise appears to not only extend lifespan but also significantly improve "healthspan" – the period of life spent in good health.
Lieberman emphasizes that it's never too late to start benefiting from exercise. Even individuals who begin exercising later in life can see significant improvements in their health and physical capabilities. He encourages readers to view exercise as a form of preventative medicine, capable of warding off many age-related health issues.
Some key recommendations for staying active as we age include:
- Consistency: Regular, moderate exercise is more beneficial than occasional intense workouts.
- Variety: Incorporate different types of exercise, including cardio, strength training, and flexibility work.
- Social engagement: Exercise with friends or in groups to make it more enjoyable and increase adherence.
- Gradual progression: Slowly increase intensity and duration to avoid injury and allow for adaptation.
- Functional fitness: Focus on exercises that maintain the ability to perform daily activities.
By highlighting the importance of lifelong physical activity, Lieberman challenges the notion that decline and disability are inevitable parts of aging. Instead, he presents a vision of aging that includes vitality, independence, and good health well into our later years – achievable through consistent physical activity.
Making Exercise Fun and Necessary
Understanding that humans didn't evolve to exercise voluntarily, Lieberman offers strategies to make physical activity more appealing and sustainable in our modern lives. He argues that the key to establishing a lasting exercise habit is to make it both fun and seemingly necessary.
The challenge we face is that exercise, by definition, is voluntary physical activity. In our ancestors' time, physical activity was unavoidable – it was necessary for survival. Today, we can lead relatively comfortable lives without much physical exertion. This means we need to find ways to trick our evolutionarily-wired brains into viewing exercise as essential.
Lieberman suggests several strategies to make exercise feel more necessary:
Social accountability: Ask someone you respect to check on your progress and ensure you're meeting your goals. This creates a sense of obligation and external motivation.
Financial commitment: Sign up and pay for a race or event in advance. The financial investment can make training feel more necessary, as you'll want to avoid wasting your money.
Goal setting: Set specific, achievable fitness goals. Working towards a concrete objective can make exercise feel more purposeful and necessary.
Habit formation: Integrate exercise into your daily routine so that it becomes an expected part of your day, like brushing your teeth.
However, making exercise feel necessary isn't enough on its own. To create a sustainable habit, it's crucial to make physical activity enjoyable. Lieberman points out that in hunter-gatherer societies, physical activities are often social events. Men might hunt in pairs, while women forage in groups, combining physical exertion with social interaction and enjoyment.
Here are some ways to make exercise more fun:
Exercise with friends: Working out with others can turn exercise into a social activity, making it more enjoyable and helping with accountability.
Join a team or club: Participating in team sports or fitness clubs can provide a sense of community and make exercise more engaging.
Try new activities: Experiment with different forms of exercise to find activities you genuinely enjoy. This could be anything from dancing to rock climbing to martial arts.
Use technology: Fitness apps, smartwatches, and other tech can gamify exercise, making it more interesting and rewarding.
Exercise outdoors: Many people find outdoor activities more enjoyable than working out in a gym. Activities like hiking, cycling, or even just walking in nature can be both physically and mentally refreshing.
Listen to music or podcasts: If you're doing solo activities like running or using cardio machines, entertainment can make the time pass more quickly and enjoyably.
Reward yourself: Set up a reward system for meeting your exercise goals. This could be anything from a favorite meal to a small purchase you've been wanting to make.
Lieberman emphasizes that the best exercise routine is one that you can stick to consistently. This means finding a balance between activities that challenge you physically and those that you genuinely enjoy. It's okay if your preferred form of exercise isn't the most intense or calorie-burning – consistency is more important than intensity for long-term health benefits.
He also encourages readers to be patient with themselves. Changing habits takes time, and it's normal to have setbacks. The key is to keep trying and to adjust your approach as needed until you find a sustainable routine.
By making exercise both fun and seemingly necessary, we can overcome our evolutionary predisposition to conserve energy and create lasting habits that support our health and well-being in the modern world.
Conclusion: Embracing Exercise in the Modern World
In "Exercised," Daniel Lieberman presents a compelling case for why physical activity is crucial for human health, despite our evolutionary inclination to conserve energy. By understanding our evolutionary history and the reasons behind our complex relationship with exercise, we can develop more effective strategies for incorporating physical activity into our lives.
Key takeaways from the book include:
Humans didn't evolve to exercise, but to be active when necessary. This explains why many people struggle with maintaining exercise habits.
The eight-hour sleep recommendation isn't based on solid evidence. Sleep needs vary among individuals, and many people function well on less sleep.
Our ancestors weren't naturally brawny. Building significant muscle mass wasn't advantageous from an evolutionary perspective.
Walking can contribute to weight loss and maintenance, especially when done consistently and in sufficient quantities.
Running doesn't inevitably lead to injuries. With proper form and gradual progression, the body can adapt to handle significant amounts of running.
Staying active as we age is crucial for maintaining health and independence. Regular exercise can compress the period of morbidity at the end of life.
To make exercise sustainable, we need to make it both fun and seemingly necessary. This can be achieved through social engagement, goal-setting, and finding activities we genuinely enjoy.
Lieberman's work challenges us to rethink our approach to physical activity. Instead of viewing exercise as a chore or a punishment, we can see it as a celebration of our bodies' capabilities and a key to unlocking better health and longevity.
The author encourages readers to keep things simple. Rather than obsessing over the perfect workout routine, focus on a few basic principles: exercise regularly, prioritize cardio but include some strength training, and maintain activity levels as you age. This straightforward approach can yield significant health benefits without unnecessary complexity.
Ultimately, "Exercised" provides a framework for understanding why exercise can be challenging and how we can work with, rather than against, our evolutionary heritage to lead healthier, more active lives. By embracing physical activity in ways that align with our biology and personal preferences, we can enjoy the numerous benefits of exercise while overcoming the instinctual barriers that often hold us back.
As we navigate the unique challenges of modern life, Lieberman's insights offer a valuable perspective on how we can harness the power of exercise to improve our health, extend our lives, and enhance our overall well-being. Whether you're a fitness enthusiast or someone who has always struggled with exercise, "Exercised" provides a fresh, science-based approach to physical activity that can help you develop a more positive and sustainable relationship with movement.