Abstract
Most of the human population in the western world has access to unlimited calories and leads an increasingly sedentary lifestyle. The propensity to undertake voluntary exercise or indulge in spontaneous physical exercise, which might be termed "exercise salience", is drawing increased scientific attention. Despite its genetic aspects, this complex behaviour is clearly modulated by the environment and influenced by physiological states. Inflammation is often overlooked as one of these conditions even though it is known to induce a state of reduced mobility. Chronic subclinical inflammation is associated with the metabolic syndrome; a largely lifestyle-induced disease which can lead to decreased exercise salience. The result is a vicious cycle that increases oxidative stress and reduces metabolic flexibility and perpetuates the disease state. In contrast, hormetic stimuli can induce an anti-inflammatory phenotype, thereby enhancing exercise salience, leading to greater biological fitness and improved functional longevity. One general consequence of hormesis is upregulation of mitochondrial function and resistance to oxidative stress. Examples of hormetic factors include calorie restriction, extreme environmental temperatures, physical activity and polyphenols. The hormetic modulation of inflammation, and thus, exercise salience, may help to explain the highly heterogeneous expression of voluntary exercise behaviour and therefore body composition phenotypes of humans living in similar obesogenic environments.
Highlights
Ancient man was a hunter-gatherer, often travelling long distances to find food, avoid threats and seek shelter
The modern western environment contains almost unlimited supplies of foods containing high level of saturated fats, salt and refined sugars. This appears to be coupled with a reduction in the consumption of plant products including fruits, nuts and vegetables. The result of this obesogenic environment is a burgeoning rise in lifestyle-induced diseases that are generally associated with energy imbalance, abnormal fat deposition and inflammation
One field of emerging interest in obesity research is the study of what motivates people to undertake voluntary physical activity, or display spontaneous physical activity
Summary
Ancient man was a hunter-gatherer, often travelling long distances to find food, avoid threats and seek shelter. As has been previously suggested [96], it could represent an anorexic “flee from famine” phenotype - in humans this may be represented by those addicted to exercise, while in the wild it might be represented by a migratory phenotype in some species It would be triggered by environmental stimuli such as famine, or possibly, even drought or factors that might induce an animal to move from danger (i.e. enforced physical activity, such as unacceptable levels of predation or competition). The Arab ethnicity appears to be particular affected [103,104] In these countries it is possible that rapid economic growth has enabled a constant supply of water, the use of air-conditioning and the adoption of a western diet: drought and heat may have been important daily hormetic stimuli in these regions (both directly, and indirectly via food plants and animals), which have been removed. Human intelligence has enabled us to remove most stressors from the environment, common sense may be required to re-introduce some of them
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