By Dr. Eddie Chaloner - Consultant Vascular Surgeon
All animals engage in physical activity, but only humans exercise, where exercise is defined as discretionary expenditure of energy to sustain or improve health. In recent times, scientists have been able to measure exercise induced changes in many physiological parameters which enhance human health and extend active life.
Debate continues about what type of exercise and how much activity per week is optimal, but most public health bodies advise citizens that 150 minutes per week of moderate physical activity promotes a healthy lifestyle into older age. The exercise industry is certainly big business – estimated to turn over £2 billion per year in the UK alone. Yet the rising prevalence of obesity suggests many people are resistant to the message. Given the clear and obvious benefits of exercise, why should that be?
Professor Daniel Lieberman, an evolutionary biologist at Harvard University thinks exercise aversion may be a biological phenomenon, stemming from the evolutionary impulse to conserve energy. If we consider the evolutionary pathway of humans from our primate ancestors, the main difference between humans and apes is our bipedal gait. Fossil records of early humans show skeletal adaptations reflecting a change from knuckle walking to upright walking, which is more energy efficient than walking on all fours.
Major evolutionary adaptations happen in response to a change in environmental circumstances, rather than by random chance. It is thought that the change to an upright posture was advantageous in Africa about 7 million years ago, when forests were receding in favour of a savannah type landscape - early humans had to move further to find food than chimpanzees living in forests and walking on two legs was highly energy efficient. Comparisons of gait and energy expenditure during movement between humans and animals show we are biologically adapted for walking and endurance running.
From the evolutionary perspective, the purpose of physical activity is to acquire food, in order to enhance reproductive fitness and maintain the species – simply put, the evolutionary process converts energy into children. Excessive physical activity wastes energy, so there is an evolutionary advantage to being inactive and conserving energy. Any dog owner knows that dogs need a daily walk, but are then content to lie around doing nothing for the rest of the day.
Studies on Hadza and San hunter-gatherer societies in Africa show that total physical activity levels are approximately twice that of Western populations. Interestingly however, the total energy expenditure per lean body mass is very similar, suggesting a more complex relationship between diet, physical activity and obesity than has generally been believed. A key observation is that older members of these primitive societies remain physically active well into their later years. Hunter-gatherers are not physically active because they enjoy walking and running, but because they have no choice – if they don’t move, they don’t eat. Once they have secured sufficient food for the day, Hadza people are entirely content to sit around doing nothing –hunter-gatherers are highly physically active well into old age, but they don’t do discretionary exercise.
Until relatively recently in human history, physical activity in Western societies was unavoidable – only a tiny elite were able to procure food without having to actively go and get it themselves. In modern society, there is no requirement for people to walk 10 miles a day to get food, so quite logically (in evolutionary terms), they chose not to expend energy unnecessarily. If Deliveroo and Just Eat deliver food to your door, why would you forage for yourself? If the train or bus takes you to work, why walk? If the washing machine cleans your clothes and the dishwasher deals with the washing up, no need to expend energy on that either.
Unfortunately, this creates a mismatch between what humans are designed and adapted for and our current environment. Simply put, the mismatch hypothesis suggests our genes haven’t been able to adapt fast enough to a rapidly changing environment where energy expenditure is discretionary, not mandatory.
Obesity and its attendant multiple diseases are the result of the mismatch. To correct the mismatch, humans living in post-industrial societies have to consciously expend energy by discretionary physical activity (exercise) and avoid calorie dense processed foods, which in evolutionary terms are quite tempting!
Physical activity is unquestionably fundamental in avoiding diseases of modern lifestyle, but the choice to expend energy in discretionary exercise is counter-intuitive – quite simply, humans have not evolved to exercise. In evolutionary terms, the couch potato may be taking the rational option and the lycra enthusiast is behaving oddly. As Lieberman points out, understanding the evolutionary basis of physical activity reveals the requirement to incentivise humans in favour of physical activity, either by emphasising the social aspects of exercise, or by facilitating walking and cycling where possible in everyday life. Show me the incentive, I’ll show you the outcome.
Published by By Dr. Eddie Chaloner, Consultant Vascular SurgeonMA(Oxon) BM BCh FRCS(Edin) FRCS (Gen)About Dr Loxley @drloxleycare www.drloxley.com
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