An interesting question I was asked the other day was ‘how much exercise do we really need’? This was a seemingly obvious question I had not been asked before, so I set about the task of doing some digging. Over the last couple of centuries, we’ve become more and more sedentary, and the big shift seems to have occurred in the last few decades. Clearly in the modern-day, technological advancements now also mean that we require less energy to do virtually everything. Perhaps Mark Twain the great American writer and humourist who famously said ‘whenever I feel the urgent need to exercise, I lie down until the feeling passes away’ should have been alive today! We can now do all our Christmas shopping online in a matter of minutes or do our weekly food shop in just a few clicks without expending a calorie (hence the Tesco’s’ strap line ‘freshly clicked’). An understanding of just how much exercise we require is becoming increasingly relevant as we do less and less. But exercise means different things to different people. Some of us run marathons, roughly 50,000 steps, or even ultra-marathons which would be roughly 200,000 steps; but obviously these are extreme examples. In the UK, according to NHS statistics most of us walk between 3000-4000 steps a day. Even this may be slightly optimistic, as according to research published by Cancer Research UK in 2017 a poll of 2,198 adults reported that 52% of adults in the UK walk about 2000 steps (or a mile) in a day and 17% said they walked less than 500 steps or a quarter of a mile. Meanwhile, according to the UK National Obesity Forum a person who walks between 7,000 to 10,000 steps a day qualifies as “moderately active”. Certainly, popular culture seems to dictate we should be fixated on 10,000 daily steps, this has also been heavily promoted by devices like FitBits. But where does this myth of 10,000 steps come from and is there any sound science behind it?
The answer is stranger than you might think. The actual basis for this myth came from a marketing campaign devised to promote the first ever wearable pedometer (called a ‘Manpo-kei’). This was released in Japan by a company called Yamasa after the Tokyo Olympics in 1964. In fact, it has even been speculated that this figure was chosen because the Japanese character for 10,000 apparently looks like a walking man and 10,000 is a lucky number in Japanese culture! There was some initial research done at the time which supported their theory. This was done by a research team at Kyushu University of Health and Welfare in Japan. They concluded that the average Japanese person took between 3,500 and 5,000 steps a day, and that if these people increased their daily step count to 10,000, it could decrease their risk of coronary artery disease. Surprisingly this all that the holy grail of 10,000 steps is based on. Oddly the World Health Organization, the American Heart Foundation and the US Department of Health & Human Services have all gradually adopted 10,000 steps as a daily activity recommendation in recent years. However, the veracity of this number has been increasingly called into question. In 2018 for example, Mike Brannan, national lead for physical activity at Public Health England even declared: “There’s no health guidance that exists to back it.” One of the major problems with the 10,000-steps-a-day goal is that it doesn’t consider the intensity of exercise. Getting out of breath and increasing your heart rate may well be even more important than the exact number of steps taken. Researchers are even currently conducting studies to see whether people who take 10,000 steps a day merely by pottering around their house achieve the same health benefits as those who do so by brisk walking or playing sport. So, this brings back to same question. How much exercise do we need? I personally I think the answer lies with evolution. The question should be ‘what were we designed to do’? This answer is not quite so straight forward.
Resting, in evolutionary terms, is just as important as exercise, so perhaps this is a good place to start. From a purely evolutionary perspective being lazy makes perfect sense as we are hard-wired to conserve energy. Other primates, such as the great apes, are exceedingly proficient at this pastime and sleep or rest 18 hours a day. Male lions, perhaps the true masters, sleep up to 20 hours a day while lionesses only manage a humble15-18 hour! It is unreasonable to compare ourselves with these apex predators, but modern humans evolved in a time when food was scarce (we didn’t have the option of strolling down to Aldi!). We didn’t use energy unless it was strictly necessary and in a hunter gatherer society you certainly didn’t disappear off in a cloud of dust and run a half-marathon for the sake of it. We were programmed to conserve energy as it allowed us to be more efficient at surviving, looking for food and shelter, avoiding predators and reproducing. In a hunter gatherer society, there is a fine balance between the energy you conserved and the energy that was used to survive. In evolutionary terms, the time spent doing all the hard work finding food was rewarded in several ways. The more work that you undertook implied that you found more food, prompting more offspring which is a key evolutionary driver. Our physiology promoted this hard work by rewarding us with endorphins that make us feel euphoric after exercise. Our endogenous endocannabinoid system (ECS) also comes into play and benefits the body by mediating some of the discomfort and chronic inflammation caused by exercise. Exercise also helps us to moderate stress. It helps control levels of reproductive hormones and it may even confer a neurological benefit by increasing blood flow to our central nervous system. Obviously, it also keeps our muscles strong and maintains aerobic fitness, both of which are important for cardiovascular health. Surprisingly we can still peep into this evolutionary window.
The Hadza tribe in East Africa represent one of the last hunter-gatherer populations on Earth. They live on fringes of the Ngorongoro Crater on the edge of the Great Rift Valley. They are also a good reference point for the rest of us. University of Arizona anthropologist David Raichlen and his collaborators, Brian Wood of Yale University and Herman Pontzer of Hunter College, spent several years studying the lifestyle of the Hadza. Their observations provide a glimpse into how our ancestors lived tens of thousands of years ago, and how that way of life may have impacted human evolution, especially with regard to exercise and health. David Raichlen explains; “Our overall research program is trying to understand why physical activity and exercise improve health today, and one arm of that research program aims to reconstruct what physical activity patterns were like during the evolution of our physiology. The overarching hypothesis is that our bodies evolved within a highly active context, and that explains why physical activity seems to improve physiological health today.”
Their research, published in the American Journal of Human Biology in 2016, detailed how much time the Hadza spend engaged in moderate-to-vigorous physical activity (or MVPA). The used heart rate monitors and GPS trackers to monitor their activity levels (I wonder what the Hadza thought of that!). This enabled a good understanding of the cardiovascular intensity that the Hadza people undertook. MVPA, as it turns out, is a strong predictor of cardiovascular health. The U.S. Department of Health and Human Services recommends that people engage in 150 minutes per week of moderate intensity activity (about 30 minutes a day, five times a week) or about 75 minutes per week of vigorous intensity activity, or an equivalent combination of the two. The Hadza, on the other hand, meet those weekly recommendations in a mere two days, engaging in about 75 minutes per day of MVPA, researchers found. Coincidentally when the researchers also screened the Hadza population there appeared to be a very low rate of heart disease. This is consistent with current research where aerobic activity is seen as a key element necessary to a healthy lifestyle. David Raichlen stated; “They (the Hadza) have very low levels of hypertension. In the U.S., the majority of our population over the age of 60 has hypertension. In the Hadza, it’s 20 to 25 percent, and in terms of blood lipid levels, there’s virtually no evidence that the Hadza people have any kind of blood lipid levels that would put them at risk for cardiovascular disease (or CVD).”
Ironically there is one aspect that does not change despite all the exercise the Hadza do. They burn the same number of calories as adults in Europe and America even though they are five to ten times more active. Now that is counterintuitive, but their bodies have accommodated their lifestyles by spending much less energy on other tasks so overall the number of calories they exhaust are the same each day, but how they spend them is different. While physical activity may not be entirely responsible for their low risk levels of CVD (diet and other factors may also play a role) exercise does seem to be important. They also never appear to be affected by diabetes. However they do have limited access to medicine, so while all this seems very enviable, curable conditions like acute infections are responsible for mortality rate. This is significant because our physical activity levels have drastically declined as we have transitioned from hunting and gathering to farming to the Industrial Revolution to where we are today.
For most the activity levels of the Hadza seems like an enormous amount but people who manage it do get huge benefits. There have been many studies which appear to validate this. Scientists who have studied the Amish people in Canada, who use no motorised forms of transport, have found that they average 14,000-18,000 steps a day and appear fitter and healthier. A study of Japanese patients with type 2 diabetes from the mid-90s found that those who averaged about 19,000 steps a day had far better outcomes compared with those who remained largely sedentary. It has been almost 70 years since the publication of the London Transit Worker Study, a famous work in which researchers tracked the heart health of London bus drivers and conductors. They found that the conductors, who walked up and down bus aisles throughout the workday, were substantially less likely to develop or die from heart disease than the drivers, who sat almost constantly while at work.
Another interesting study was also published in 2017 in the The International Journal of Obesity by researchers at the University of Warwick. This compared Glaswegian mail carriers who cover their routes on foot with the mail service’s office workers. This sharp contrast between these two groups provided insights into the links between activity and health. They began by recruiting 111 of the postal-service workers, both men and women, and most between the ages of 40 and 60. None had a personal history of heart disease, although some had close relatives with the condition. The researchers measured volunteers’ body mass indexes, waist sizes, blood sugar levels and cholesterol profiles, each of which, if above normal, increases the chances of cardiac disease. Then they had each volunteer wear a sophisticated activity tracker for a week, while at work and at home and during the weekend.
They calculated how many steps each person had taken each day. Not surprisingly the variations turned out to be considerable. Some of the office workers sat for more than 15 hours each day between work and home, while most of the mail carriers barely sat at all during working hours. These differences were echoed in the volunteers’ risk factors for heart disease, the researchers found. Those workers who sat for most of each day tended to have much larger waistlines, higher B.M.I.’s and worse blood sugar control and cholesterol profiles than those who frequently stood and moved, even after then researchers accounted for age, family history, late-night shift work (which is known to affect heart health) and other factors.
The risks were magnified at the extremes. For every hour beyond five that workers sat each day, the researchers found, they added about two-tenths of a percentage point to their likelihood of developing heart disease, based on their cumulative risk factors. But the greatest benefits came from the most exaggerated amounts of activity. Those mail carriers who walked for more than three hours a day, covering at least 15,000 steps, which is about seven miles, generally had normal body mass indexes, waistlines and metabolic profiles. Together, these factors meant that they had, effectively, no heightened risk for cardiac disease.
Two hours brisk walk or 15,000 steps seems like quite a lot to achieve for many of us. The whole point of this is probably that some exercise is better than none. Research consistently demonstrates that even moderate exercise confers significant health benefits and even an extra 30 minutes exercise a day that raises your heart rate effectively halves your mortality rate. As for The Hadza, how long their lifestyles are maintained remains to be seen. They have been under pressure by the Tanzanian government to forgo the hunter-gatherer lifestyle. Incredibly most of these attempts have failed. Of the fewer than 1,000 Hadza left, an estimated 300 to 400 of them are still full-time hunter-gatherers.