Physical activity is now considered one of the “big four” lifestyle factors (along with smoking, nutrition, and drug abuse) that have major effects on health. In 2015, the Academy of Medical Royal Colleges put out a report summarizing the benefits of exercise, calling it both a “miracle cure” and a “wonder drug.”  The report observes that regular exercise can prevent dementia, type 2 diabetes, some cancers, depression, heart disease, and other common serious conditions — reducing the risk of each by at least 30%. This is better than many drugs.
A recent analysis of data from more than 60,000 respondents found that people exercising 1-2 times per week had a 30% reduction in all-cause mortality compared to those who got no exercise. There was a 35% reduction for people who exercised 3-5 times.  Similar studies have concluded that a sedentary lifestyle is a primary cause of 36 diseases, and that exercise is an effective treatment to prevent them. [3, 4] Numerous experts have observed that if exercise came in a pill, it would be the most effective and widely prescribed medicine ever developed.
While the evidence supporting the health benefits of exercise is undeniable, I don’t find the metaphor of it being “medicine” totally appealing. First, medicine is something most people would rather not take, so the marketing is not very good. Second, the term medicine suggests cure of a particular disease, which is misleading.
Physical activity can improve your health in many different ways, just as light, water and soil will nurture a plant. But it’s not a targeted intervention that “fixes” a specific problem.
I think a better metaphor for the benefits of physical activity is one recommended by Katy Bowman and Nick Tuminello: movement is like food. This analogy works on many different levels. First, nutrients in food are beneficial when consumed in some goldilocks amount — not too much and not too little. For example, you need a minimum dose of iron to avoid anemia, but too much is toxic. Many kinds of inputs to the body follow this pattern, even water. With physical activity, some minimum amount is essential, too much is toxic, and there is a broad range of happy mediums.
Another analogy between food and movement is that you need a well-balanced diet of many different nutrients, all of which have a different optimum dose. If you have a deficiency in Vitamin A, it won’t help to double up on Vitamin B. The same is true of physical activity. The bench press is a fine exercise, but if that’s all you ever did, you would become deficient in other areas of physical function.
If movement is like food, how do you eat a balanced diet? Part of the answer is that … it depends. A twenty-year-old athlete will need a different diet of movement than a 65-year-old with knee pain. In fact, two 65-year-olds with knee pain might benefit from completely different programs. To find what works best for an individual, you will need to explore a wide landscape of different options. The good news is that some parts of the landscape are more worth exploring than others. To get a rough idea where they are, we can look to two sources of data: (1) formal recommendations from government health groups; and (2) research analyzing the physical activity of hunter-gatherers living in natural environments. I think of these guidelines as major landmarks for orientation on the movement landscape. Fortunately, they both point in the same basic direction.
Recommendations From Health Groups
Numerous governmental agencies, including the World Health Organization, the U.S. Department of Health Services, and the National Health Service in the U.K., have published physical activity guidelines. [5, 6] They are based on expert analysis of the voluminous research looking at physical activity, fitness, and health. Here is a brief summary of their advice, which is almost the same for each source.
The guidelines suggest at least 150 minutes per week of “moderate” physical activity or half as much “vigorous” activity. (See below for definitions.) But this is just the minimum, and a better goal would be 300 minutes of moderate activity per week. Adding more exercise may continue to reduce mortality until as much as 750 minutes per week, after which point the health benefits of physical activity seem to flatline. 
“Moderate” Activity Defined
Moderate activities are usually light aerobic exercise — continuous cyclic movements done at an easy pace. Examples include:
gardening or yard work
jogging, cycling, or swimming at an easy pace
Moderate exertion feels like you are working, but not in a way that is unpleasant or difficult to continue. Heart rate is about 60-80% of maximum, and breathing rate is elevated to a point where it would be difficult to sing, but easy to talk. You may break a light sweat but will not become significantly overheated. After finishing a session of moderate physical activity, you could probably complete another one if necessary.
“Vigorous” Activity Defined
Vigorous activity is higher intensity work that can be either continuous or intermittent. Examples include:
resistance training with weights, machines, bands, or bodyweight
sprinting or high-intensity interval training on a cycle or rowing machine
continuous running, cycling, swimming, or rowing at a challenging pace
heavy manual labor
During continuous vigorous activity such as running or cycling, you are approaching the fastest pace you can sustain for twenty or more minutes. Your breathing rate is high enough that you cannot have a conversation. Intermittent activities like weight lifting, sports or sprinting cannot be performed continuously, but only in intervals. Vigorous physical activity feels hard and requires willpower to continue. When you are finished, you will probably want to rest at least a day before completing a similarly tough workout.
Movements That Challenge Strength
Most guidelines recommend that the above weekly totals should include at least two sessions that maintain or build strength in all major muscle groups. Although the majority of research on physical activity relates to aerobic exercise, there is a large and growing number of studies showing equally impressive health gains from strength training. Some of these benefits are not available with aerobic exercise, especially preservation of muscle mass, which declines with age, often to a point where function is significantly compromised. 
Movements That Challenge Mobility And Basic Coordination
Some popular guidelines, but not all, recommend inclusion of movements that maintain functional ranges of motion, and basic movement skills like squatting or single-leg balance. This doesn’t mean you need exercises specifically devoted to this purpose, such as stretching or corrective exercise. Many common activities challenge mobility and functional movement skills, including dancing, swimming, martial arts, gymnastics, climbing, calisthenics, or classic compound strength exercises like pushups, pull-ups, rows, presses, squats and lunges. On the other hand, if all you do is bike or run, you will not be challenging your mobility or coordination very much.
Physical Activity Levels Of Hunter-Gatherers
Another way to approach the question of how to move is to consider the physical activity levels of humans living in more natural environments. This is the same logic you would apply to analyzing the health needs of any other animal. If you had a pet cheetah and wanted to know how much running she should do to maintain good health, you would try to learn something about how much cheetahs run in the wild. If you had a pet chimp, you would take him to the climbing gym, not the swimming pool.
Anthropologists who study hunter-gatherer cultures observe that they generally enjoy excellent health and fitness, and have low to non-existent rates of chronic diseases associated with a sedentary lifestyle.  They engage in high levels of physical activity, but certainly do not consider it to be exercise or medicine.  Movement is simply inseparable from almost every meaningful event in their lives. Although each hunter-gatherer culture has a different lifestyle, there are some general patterns and averages that are informative.
Men usually spend the day hunting, which requires lots of walking, occasional jogging, and the odd sprint. They sometimes climb trees, dig to find tubers, and carry food back to camp, which must be butchered. Women generally spend their days gathering plants and also caring for young children, who often must be carried. Back at camp, men and women engage in toolmaking, and food preparation. Downtime is spent sitting on the ground in positions like squats that challenge lower body mobility. 
Although they are moving all day, the pace is not grueling. Recent studies on the Hadza tribe in Tanzania show that they do about 135 minutes per day of moderate to vigorous physical activity.  That’s about 900 minutes of activity a week, just a bit past the point at which recent studies have found that adding more exercise stops providing any significant additional health benefits in terms of reduced mortality.
Some days involve hard work, but they are usually followed by easy days. Presumably, some days will involve maximum intensity effort, such as sprinting or carrying a heavy load. Interestingly, activity levels do not decline much with age. The 65-year-old elders keep up just fine with the young adults. A good percentage of the total workload is walking 5-10 miles per day. If you think in terms of steps, this is about 10 to 20,000.
How does this organic, all-natural program for fitness compare to the standard-issue government cheese? There are some obvious similarities. The majority of the work is moderate continuous movement like brisk walking. Vigorous activity is a smaller percentage of the whole and includes work that challenges strength (climbing, digging, carrying, butchering) or power (sprinting).
Many of the activities require mobility, coordination, and balance, such as walking over uneven terrain, climbing, and scrambling, digging, lifting and carrying odd-shaped items, throwing, and sitting on the ground. One major difference is that hunter-gatherers do a higher volume of low-intensity work, even compared to highly active modern humans. They are not doing more bench presses, but they are getting in more steps.
Interestingly, walking is exactly the type of physical activity that modern humans would probably like to do quite a bit more, if only they had the time. Paddy Ekkekakis studies motivation to exercise and observes that although high-intensity exercise is quite effective at delivering health benefits quickly, most people don’t do it because … (prepare to be shocked) … they don’t like it. But people tend to enjoy walking. Under the right circumstances, say being with a friend in a nice environment, they do not consider it to be exercise at all, but an enjoyable and invigorating experience that delivers immediate rewards.
Another notable feature of walking is that it provides health benefits with only a minimal risk of injury. More intense exercise (e.g., a set of barbell squats) offers a relatively narrow window between too much and not enough. The difference between a good workout and an injury might be just a few extra reps or plates on the bar. But the margin of error with walking is huge. After a healthy dose of walking, most people could double it and recover easily.
It makes sense that walking delivers the highest bang for your buck because this is the movement we are best adapted to perform. Like any other animal, our primary physical function is locomotion, and walking is the most energetically efficient way to get the job done. If you did nothing else but walk a lot, you’d be in better shape than most Americans.
A Quick Summary
If you want to “play” with fitness as a way to improve general health, here are some “rules of the game” to keep in mind. Have as much fun as possible within these basic constraints:
Aim for at least half an hour and up to two hours of physical activity almost every day.
Movement should be varied in terms of volume, intensity, and type. Most activity can be fairly light. Walking is the most natural and beneficial movement for human beings.
Every few days, include some high-intensity work that significantly challenges your strength, power, and/or capacity to sustain high energy output for a short period of time. Climbing, running and resistance training are logical choices.
Include movements that challenge coordination, balance, and range of motion.
Or to put this in even simpler terms:
Move around a lot at a slow easy pace.
Frequently move with some urgency or pick up something heavy.
Every once in a while, move like your life depends on it.
And have fun!
Physical activity isn’t like taking medicine, you know.
The preceding was an adapted excerpt from my new book called Playing With Movement: How to Explore the Many Dimensions of Physical Health and Performance.