Physical Activity and Obesity

Obesity is a major risk factor for development of type two diabetes. An inactive lifestyle also predisposes for type two diabetes and both physical activity and obesity are therefore, important topics in relation to prevention of type two diabetes. 

1)Explain health benefits of being physically active.

2)Describe how physical training affects energy balance and metabolic health and discuss the
potential of physical training in prevention and treatment of obesity and diabetes.

3)Demonstrate methods that can be used to evaluate physical fitness, body fat distribution and 
    insulin sensitivity. 

Physical activity should preferably be part of a healthy lifestyle on a daily basis. Major health agencies like the World Health Organization recommend that adults throughout the week should do at least 150 minutes of moderate intensity or at least 75 minutes of vigorous intensity aerobic physical activity or a combination.

The activity should be performed in bouts of at least 10 minutes duration and preferably be spread on days throughout the week. Additional health benefits can be obtained with a high activity level.

Additionally, muscle strengthening activities should be performed two or more days a week.
Examples of physical activity include dancing, hiking or swimming in leisure time, walking or cycling for transport, occupational activities and daily activities as household chores, games and sports activities. Seniors aged 75 and above are recommended to aim for similar activity level as other adults and in addition to exercises to enhance balance and prevent falls, at least three days per week. When older adults cannot do the recommended amount of physical activity due to health conditions, they should be as physically active as their abilities and conditions allow.


Children and young people up to the age of 18 years should accumulate at least 60 minutes of moderate to vigorous intensity physical activity per day. Activities include games, sports, transportation, chores and many more activities in the context of family, school and community.
At least three times per week, the intensity of the activities should be vigorous and aim at strengthening skeletal muscle and bone.  

Additional physical activity provides additional health benefits.

A practical way of assessing one's activity level is by wearing a pedometer. A number of 10,000 steps has been marketed as a magic number of steps. Walking ten thousand steps per day will most certainly be beneficial to health, but it's difficult to directly relate numbers of steps to minutes of exercise and health benefits as this depends on walking, running speed, body weight and composition, physical fitness and other individual factors. Physical fitness can be evaluated
by a variety of methods. Some are easy to use and cheap, but not very precise. Other methods are more precise,but require special equipment and are not feasible in larger groups of subjects.

A simple way to evaluate physical activity level is by using a questionnaire in which the subject responds to questions about his or her exercise. Examples of such questionnaires are the International Physical Activity Questionnaires, IPAQ and the Recent Physical Activity Questionnaire, RPAQ. The validity of physical activity questionnaires depends heavily on the eagerness of the subject to give an unbiased assessment of his or her physical activity habits. A more objective measure of activity levels can be obtained by activity sensors worn by the subject. A simple, over the counter sensor is a pedometer by which the daily number of steps can be evaluated. An accelerometer is a more sophisticated activity sensor, which can detect movement in several directions.

Accelerometry can be combined with heart rate monitoring and all GPS to increase the ability of the measurement. Lately, detection of heat flux has been included as a parameter for increasing the precision of the activity estimation. Most activity sensors can easily detect simple activities, like walking, jogging and running, but movements during cycling are more difficult to quantify  Detection of swimming activity requires that the sensor is waterproof.

An expensive, but unbiased way to measure physical activity level is by the doubly-labelled water method. The subject is to drink a glass of water labelled with stable isotopes at both the hydrogen and the oxygen atoms. Hydrogen is excreted from the body owner's water, but oxygen is excreted both via water and carbon dioxide. During physical activity, carbon dioxide is produced due to combustion of energy rich substrates. The higher the activity level, the higher the excretion of carbon dioxide. After the initial distribution of labeled water in the body and one to two weeks after drinking the labelled water, urine or saliva samples are taken and analyzed for concentrations of labeled hydrogen and oxygen. So concentration of labeled substances in these fluids reflects the concentration in the water faith of the body. The carbon dioxide excretion and hence, the total energy expenditure can be calculated as the difference between the rate of decline of labeled oxygen and hydrogen. The physical activity level is calculated by subtracting the basal metabolic rate and the thermic effect of food from total energy expenditure.

Physical performance can be assessed by testing the subject in a gym, the clinic or the laboratory. Many simple tests exist. For example, for determination of walking speed, hand grip strength or balance. The state of the art test for assessment of physical fitness is quantification of maximum oxygen uptake by indirect calorimetry during a biking or running test to exhaustion. During physical exercise, skeletal muscles require energy to contract. The main substrates expended during exercise are fat and carbohydrates, but a small amount of protein is also used. At low exercise intensity, the main substrate used is fat either from intramyocellular lipidstores or supplied by the blood. Blood lipids are either  triacylglycerol from the liver or the gastrointestinal tract or free fatty acids derived from adipose tissue stores. At an exercise intensity of approximately 40 to 50% of maximal oxygen uptake, fat oxidation reaches its maximum rate. As exercise intensity increases, more energy is needed in the contracting muscles.

At higher exercise intensities, less fat and more carbohydrate will supply the energy for muscle contractions. Carbohydrates are derived from skeletal muscle glycogen stores or provided by the blood as glucose. Blood glucose stems from liver glycogen stores or from the gastrointestinal tract after carbohydrate containing drink or meal. Body glycogen stores are limited and when exercise time is increased, less and less glucose and more and more fat will be used. The energy stored in fat can only be released aerobically, meaning by use of oxygen for combustion. In contrast, glucose can be degraded both aerobically and anaerobically. Therefore, both fat and carbohydrate can supply the muscles with energy at low exercise intensities when the aerobic demand is low versus high intensities. Mainly glucose is used. When degraded anaerobically, glucose is turned into lactate. At higher exercise intensities, the aerobic demand is increasing and at a certain intensity called the anaerobic or the lactate threshold. Lactate will start to accumulate in the blood. Untrained individuals have a low anaerobic result at approximately 50 to 60% of maximal oxygen uptake, but physical training can increase this. That means that well-trained individuals can sustain a given exercise pace for a longer period of time. At very high exercise intensities and at the onset of exercise, energy is supplied by local muscle stores of keratin phosphate and ATP. These stores contain very limited amount of energy. I will now explain in detail health benefits of being physically active. Physical activity is healthy for young and elderly, slim and obese, healthy and sick. Muscles are meant to be used and if you don't use them, you lose them. Also, the rest of the body will degenerate, if it's not stressed regularly. Physical activity will affect nearly all organ systems of the body and keep you used both in prevention and treatment of a variety of diseases and physical activity prolongs life. Load bearing physical exercise will increase the bone mineral content and reduce the risk of osteoporosis. Also, tendon and skeletal muscle strength will increase after physical exercise. 
Similarly, the heart muscle will become stronger and can hence deliver a higher stroke volume during every heartbeat. This will decrease heart rate, the blood pressure can be lowered by physical exercise. More in hypertensive than in non-hypertensive persons. The plasma concentration of the good lipoprotein, HDL cholesterol is increased. Various the concentration of the bad lipoprotein, LDL cholesterol and triglyceride in blood have decreased. The risk of atherosclerosis is reduced by physical exercise and thereby, the risk of cardiovascular diseases and stroke. Energy is expended during exercise moving the energy balance in a favorable direction for prevention and treatment of obesity. Moreover, insulin sensitivities increased by physical exercise, both acutely and in the long-term and this effect of physical exercise is effective both in preventing and treatment of type two diabetes. Physically fit persons also have a lower
probability of developing some cancers, especially breast and colon. Additionally, physical exercise can increase mood and self-esteem and maybe also libido and reduce the risk for depression.

 

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