Physical activity and health: Shifting focus from modern era to Stone Age life style

Physical activity is essential in life to stay healthy and maintain our normal behavior. Physical activity is defined as any bodily movement produced by skeletal muscles that require energy expenditure. It should not be mistaken with “exercise”, which is a subcategory of physical activity. A number of studies from animals to humans revealed the benefits of physical exercise for various health disorders. This paper discusses the lifestyle practices and food which was practiced during Stone Age and the reasons for physical inactivity in the modern era. In addition, the metabolic health benefits of physical exercise learnt through animals and human experiments have been discussed.


Introduction
Physical activity is essential in life to stay healthy and maintain our normal behavior. Physical activity is defined as any bodily movement produced by skeletal muscles that require energy expenditure. It should not be mistaken with "exercise", which is a subcategory of physical activity. A number of studies from animals to humans revealed the benefits of physical exercise for various health disorders. This paper discusses the lifestyle practices and food which was practiced during Stone Age and the reasons for physical inactivity in the modern era. In addition, the metabolic health benefits of physical exercise learnt through animals and human experiments have been discussed.

Stone age: Paleolithic lifestyle
During Paleolithic (palaios: old; lithos: stone) era people used stone to make their tools to meet basic needs for food, shelter, and clothing. The physical activity of old stone age people depends on their ability to hunt or gather food, produce water, build and maintain clothing and shelter, escaping from predators and enjoying social interaction. Barefoot walking had strengthened their muscles, tendons and general co-ordination, reducing the possibility of developing acute/chronic health disorders. They prepare their healthy balanced diet preferably from natural sources which are minimally processed. Therefore, the contribution of both energy intake and expenditure turned balanced and is a vital component to maintain their health. It was estimated that one-third of their energy intake was spent on physical activity. Intermittent fasting was practiced by our ancestors and few groups of people till date, which significantly helped to control the variety of health indicators including glucose, cholesterol, triglycerides and other metabolites. Regular exposure of skin to sunlight is necessary to produce vitamin D, which boosts the immune system, prevents cancer and aids in bone growth/repair. Lack of (sun) light has also been shown to be a cause of depression and lack of sunlight during winter results in reduced Vitamin D synthesis and immunity leading to onset of "flu" during this season. Cold baths have shown to enhance the immune system and hot baths promote the release of "heat shock proteins" that protect and repair damage in the body's cells. All the above said factors are accomplished in those days.

Modern era: Sedentary lifestyle
In the modern era, advancement in technology has directed us to lead sedentary lifestyle and has resulted in marked decline in our regular physical activity and food habits compared to the Paleolithic life style. Physical inactivity over a longer period of time has been identified as a risk factor for the development of non-communicable diseases such as heart disease, diabetes, cancer and obesity. The major reasons for physical inactivity are due to insufficient participation in physical activity, sedentary lifestyle and increased use of passive modes of transport. Increased urbanization such as violence, heavy traffic, air pollution, lack of parks, sidewalks and sports/recreation facilities are also considered to be the major reasons for the decline in physical activity. Physical inactivity tends to increase with age and sedentary lifestyles are more likely to be lead by females than men. The sedentary life style has high calorie rich diets such as grain and milk based foodstuffs, sugars, vegetable oils, processed foods with additives that may interfere with their metabolism. These foods also contain easily digestible carbohydrates which increase the glucose levels in blood and further stored as fat by the action of insulin. Chronic intake of such foods could lead to metabolic disorders. thereby act as an agent for improving physical activity and change in their lifestyle [2]. Pet walking have improved the children's physical activities; among obese children's [3,4] and elderly [5]. Pet-assisted therapy for hospitalized children's with cancer has alleviated their emotional distress, facilitated their adaptation to the healing process and promoted their well-being [6]. Pet-assisted therapy on trauma symptoms for sexually abused children's have shown to decrease their trauma symptoms such as anxiety, depression, anger, post-traumatic stress disorder, dissociation, and sexual concerns [7]. Non-pet walkers are self-reported to possess risk indicators that may lead to diabetes mellitus, hypertension, hypercholesterolemia and depression compared to dog walkers [8]. Owing a pet ownership have improved the physical activity, demonstrated life prolonging effects among heart attack sufferers [9] and elderly patients after myocardial infarction [10].

Lessons from pre-clinical and clinical research
Regular exercise training has shown beneficial anti-atrophy effects [11] in diabetic rats and improved skeletal muscle insulin resistance in obese Zucker rat rats [12]. Animal models were used to study the exercise-mediated effects on the regulation of lipid metabolism using guinea pigs [13]. Enhancement of neuronal differentiation and deteriorated motor function was observed in Parkinson's rats subjected to exercise [14]. The intensity of myocardial infarct size after was reduced after subjecting coronary artery occluded rats to forced swim test and this reduction may be correlated to increased myocardial vascularity [15]. It is evident from the above studies; exercise has positive effects to both normal subjects and subjects with altered pathophysiology.
Similarly several studies on humans also revealed the exercise has potential benefits to maintain their health and fitness. Extensive epidemiological evidence demonstrates that mild physical exercise without weight loss can be adopted as an adjunct approach in the treatment of diabetes mellitus. It increases the rate of glucose uptake into the skeletal muscles by over-expression of glucose transporter, GLUT4 to the plasma membrane [16,17]. Scientific reports have linked that regular physical exercise to various risk factors for cardiovascular disease. It promotes weight reduction, thereby reduces the blood pressure. It also the reduces the low-density lipoprotein, total cholesterol, and increase the high-density lipoprotein level in the blood [18]. Hypertensive subjects are physically inactive compared to normal subjects and studies support that hypertensive individuals need to optimize blood pressure by practicing regular exercise [19]. Chronic systemic inflammation is associated with the development of obesity and metabolic dysfunction. During obesity, increased secretion of pro-inflammatory cytokines (adipokines) from adipocytes (fat cells) [20] is accompanied by insulin resistance and glucose intolerance. Mild to chronic exercise have shown to ameliorate both dyslipidemia and systemic inflammation [21]. Physical exercise might benefit obese partly through increased secretion of anti-inflammatory adipokines and decreased production of pro-inflammatory cytokines [22]. It has also been hypothesized that exercise promotes adipocyte oxidative capacity [23].

Closing comment
Its clear form the above a change in life style could keep us healthier in the modern computer world. A closer look into the Paleolithic lifestyle lead by our ancestor's revealed that balanced physical activity along with nutritious diets have helped them to stay metabolically healthy. People living sedentary life style must look into Paleolithic lifestyle which might provide the answers to keep them healthy and lead a better future. Patients with health disorders should seek the advice of physicians and health care professionals to know their food habits and get prescribed with appropriate exercises which could provide additional benefit to maintain health.