Evolution did not prepare us to become couch potatoes – our ancestors actually had to move around to find food, they couldn’t just order it over the phone. Running to hunt and gather food and fasting due to food scarcity are considered some of the biggest evolutionary energetic challenges our bodies and brains have faced.
Compared to other mammals, humans are actually ineffective sprinters – sprint running demands about twice as much metabolic energy for humans than for other similarly sized mammals. However, and unlike other mammals, humans are highly efficient endurance runners, able to run many miles over extended periods of time using anaerobic metabolism.
Among primates, endurance running is unique to humans, being also uncommon among most quadrupeds. The ability to run was most likely an evolutionary advantage: running may have helped our ancestors get close enough to their prey or compete with other scavengers; endurance running (and walking) also favored the ability to travel long distances. There is indeed strong evidence that endurance running may have had a strong impact in human evolution and that its demands may have made a major contribution to the human body’s form and physiology.
Today, endurance running, such as jogging, is not a need, but mostly a form of exercise and recreation. And it is highly beneficial: running produces metabolic improvements, including increased fitness and decreased abdominal adiposity, and promotes overall health. The rapid increase in the incidence of obesity and metabolic diseases in the last generations is attributed primarily to excessive consumption of high energy processed foods combined with sedentary lifestyles, as opposed to what evolution designed us for. Physiological benefits of regular exercise include a reduced risk of several major diseases, such as diabetes, cardiovascular diseases, stroke, and cancers.
Regular aerobic exercise can also optimize brain function and resistance to age-related diseases; it improves mood and cognitive function, and circulating factors produced by peripheral tissues in response to exercise may stimulate neuroplasticity and cellular stress resistance in the brain. Brain performance is actually at a peak level under conditions of regular vigorous energy expenditure.
Exercise and aging
Although the effect of exercise on life expectancy has been a subject of intense debate, recent data strongly supports the view that regular aerobic exercise increases lifespan and delays the effects of aging.
Aging is a physiologic state in which a progressive decline of organ functions is accompanied by the development of age-related diseases. Oxidative stress is a hallmark of aging – a standing theory postulates that aging and its related diseases are the consequence of free radical-induced damage to cellular molecules and the inability to counterbalance these changes by endogenous anti-oxidant defenses. Oxidative stress within mitochondria in cells can lead to a vicious cycle in which damaged mitochondria produce increased amounts of reactive oxygen species, which in turn increase damage. In light of this theory, increasing antioxidant defenses should allow for delayed aging and delayed onset of age-related diseases.
By increasing the levels of antioxidant enzymes and preventing age-associated decrease in antioxidant enzyme production, exercise may indeed be quite beneficial in slowing down aging. A variety of cognitive processes may also benefit from exercise throughout life. Evidence suggests that regular exercise can actually hinder age-related cognitive decline in humans.
Exercise boosts the functional capacity of the brain by acting on synapses and neural stem cells. Synaptic plasticity refers to changes that occur in the number, structure, and functional status of synapses as a response to environmental challenges, including intellectual challenges, exercise, or even traumatic brain injury or disease.
Synaptic plasticity is believed to be crucial for the preservation of cognitive abilities, including learning and memory. Brain plasticity is a potential mechanism through which brain function can be preserved or even restored in the context of aging and injury. Plasticity is thought to be maintained throughout the lifespan and to be enhanced by exercise. Indeed, animal studies have demonstrated that runner rats exhibit greater synapse strengthening; interestingly, sleep deprivation reduces synapse strengthening in sedentary rats, but this effect is counterbalanced in rats that exercise.
Neurogenesis is a process in which neural stem cells differentiate into new neurons. These newly generated neurons can then grow axons and dendrites, and form synapses with other neurons, thus becoming integrated in functional neuronal circuits. Neurogenesis in the hippocampus in the adult brain is a particularly important process for the preservation of brain plasticity.
Enhanced neurogenesis is associated with improved cognition, whereas a decline in new neuron generation is associated with aging and depression. In animal studies, running has been shown to effectively stimulate neurogenesis in the hippocampus. Although intellectual challenges can also enhance synaptic plasticity, there is evidence suggesting that physical activity may actually be more effective than cognitive stimulation in the production of new neurons in the hippocampus.
Epidemiological studies in humans have also demonstrated improvements in cognitive performance in response to regular aerobic exercise. A study that included 1820 adolescents found that cognitive performance was significantly higher for those who participated in physical sports activities during leisure time. Structural MRI studies even showed that regular aerobic exercise can increase the size of several brain regions.
Interestingly, rats that had exercised as adolescents but stopped exercising as adults maintained superior object recognition memory. On the other hand, rats that exercised only as adults also showed improved object recognition memory, but lost it within only a few weeks of ceasing exercise. This strongly indicates that exercise during a critical period of brain development may enhance cognitive function later in life. Exercise and cognitive challenges during this developmental period may therefore provide a so-called “cognitive reserve” that may protect against age-related cognitive decay.
One important additional benefit of regular physical activity is increased stress robustness. There is evidence from human and animal studies that a sedentary lifestyle is associated with stress vulnerability, whereas a physically active lifestyle is associated with increased stress resistance and stress resilience, i.e. the ability to rapidly recover and adapt. Stress is a well-known risk factor in numerous conditions, including depression, anxiety, and cardiovascular, autoimmune and neurodegenerative diseases, just to name a few.
Clearly, there is a huge amount of scientific evidence proving what we already suspected: regular physical activity is highly beneficial for the brain, the mind and the body.
“Mens sana in corpore sano.”
References
Bramble DM, & Lieberman DE (2004). Endurance running and the evolution of Homo. Nature, 432 (7015), 345-52 PMID: 15549097
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Ruiz JR, Morán M, Arenas J, & Lucia A (2011). Strenuous endurance exercise improves life expectancy: it’s in our genes. British journal of sports medicine, 45 (3), 159-61 PMID: 20876590
Ruiz JR, Ortega FB, Castillo R, Martín-Matillas M, Kwak L, Vicente-Rodríguez G, Noriega J, Tercedor P, Sjöström M, Moreno LA, & AVENA Study Group (2010). Physical activity, fitness, weight status, and cognitive performance in adolescents. The Journal of pediatrics, 157 (6), 917-9220 PMID: 20673915
Steffener J, & Stern Y (2012). Exploring the neural basis of cognitive reserve in aging. Biochimica et biophysica acta, 1822 (3), 467-73 PMID: 21982946
van Praag H, Fleshner M, Schwartz MW, & Mattson MP (2014). Exercise, energy intake, glucose homeostasis, and the brain. The Journal of neuroscience : the official journal of the Society for Neuroscience, 34 (46), 15139-49 PMID: 25392482
van Praag H (2008). Neurogenesis and exercise: past and future directions. Neuromolecular medicine, 10 (2), 128-40 PMID: 18286389
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