Physical activity plays a crucial role in a healthy life style of every person.
In fact it is postulated that physical activity should be the norm and lack of it abnormal.
Physical exercises are not only important to maintain healthy body weight, but are part of a bigger picture including prevention of many chronic diseases as well as part of body homeostasis.
Energy expenditure (EE) consists of 3 components
EE = BMR/RMR + TEF + EEA
BMR in simple words means amount of energy that body is using per minute in order to maintain the body homeostasis in a resting state. On average BMR = 1 Calorie per minute thus in 24h 1440 calories are used.
Most of the energy is used for the function of the heart, breathing and thermoregulation as well as function of the nervous and hormonal systems.
BMR is measured after a person wakes up, in the dark room, after resting and having 8 hours sleep and not eating for 12 hours.
BMR is often confused with RMR (Resting Metabolic Rate). RMR is measured under less strict conditions. The person is not required to sleep and rest for 12h prior measurement. It is more feasible test therefore becomes more commonly used than BMR.
A very simplified method to calculate RMR is by adding zero to the person’s weight in pounds.
For example if a person weighs 150 pounds, his /hers approximate RMR will be 1500 Cal.
Much more accurate method is the one described by Livingston and Kohlstadt.
“……If m = body weigh in kg and a = age in years:
the female’s RMR can be calculated by multiplying 248 times m to the power of 0.4330 minus (5.09 times a)
RMR (females) = 248 x m to the power of 0.4356 - (5.09 x a)
RMR (males) = 293 x m to the power of 0.4330 - (5.92 x a) …”
Another well known and old formula is Harris- Benedict equation.
The original formula was published in 1919, revised in 1984.
Based on revised HB formula the BMR is calculated as per below equations:
For women BMR = 447.59 + (9.25 x weight in kg) + (3.1 x height in cm) - (4.33 x age in years)
For men BMR = 88.36 + (13.4 x weight in kg) + (4.8 x height in cm) – (5.68 x age in years)
The most important factors which influence BMR/RMR are:
TEF, Thermic effect of food determines the amount of energy needed to process eaten food
(to digest, to breakdown and to store). Approximately TEF = 10% of the total calories of the meal are burned through the processing of the food.
EEA, Energy Expenditure of Activity; this will be the amount of energy needed for the body to perform daily physical activities, exercises included. 20 % of energy of RMR is used to maintain proper functioning of the muscle tissue at rest. But the moment the person starts to exercise the energy need is much higher and it will fall under EEA. Any movements of the body, even involuntary as well as keeping the posture (standing) are part of EEF.
The subject of this assessment is to discuss physical activity as a part of EE in weight control.
In recent decades it became clear that sedentary life style with a minimum physical activities leads to overweight and obesity. Sitting in front of computers, driving cars, watching TV replaced active life style which was a norm not in that far past.
Daily physical activities include:
Physical activities play a big role as a part of energy expenditure. It is said that during vigorous exercising a fit person can burn up to 1200 Cal per hour!
The amount of energy used during exercises depends on many factors. Some of them include:
Regular exercises will build muscle tissue therefore will increase RMR, but sadly once they are stopped the RMR falls to the initial levels.
Even though studies proved that the more effective way to lose weight is by changing eating habits by cutting on calories intake, the role of exercises cannot be undermined as it is also proven that regular exercises help to maintain body weight, have positive impact on reducing body fat mass (especially intra-abdominal) and have many other positive effects on a person’s health.
Few examples of positive health implications after regular exercises include: prevention and improvement in cardiovascular conditions as well as cerebrovascular, prevention and improvement in endocrine diseases, especially metabolic syndrome and diabetes, improvement in bone densitometry, prevention and improvement in hyperlipidemia and hyperuricemia and others.
There is even created a term “metabolic fitness” which indicates a state of an individual who does not suffer from hyperlipidemia, hypertension and diabetes or impaired glucose tolerance and whose fasting glucose and insulin levels are normal.
The maintenance of weight achieved by corrected diet and physical activities is much more successful if the person continues with regular exercises.
Another important benefit of intense physical activities is a metabolic phenomenon called
Excess Post- exercise Oxygen Consumption (EPOC), previously known as oxygen debt.
After vigorous, prolonged exercises, for some period, even up to 12-24h, the metabolism remains on a higher level. The same effect is seen even after light exercises, but there the response last only few minutes.
As it was mentioned already exercises performed on a regular basis will lead to increased RMR and therefore will increase energy expenditure too.
Physical activities can be measured by
MET is often described as “an index of the intensity of the physical activity”. For example MET of activity during sleeping is of 0.9. MET of 18 is for activity of a person running at 17.5 km/h.
MET of 2 indicates activities which require double energy than energy spend at rest. So the higher MET the more intense are the activities.
Light intensity activities are classified as MET less than3 and include sleeping, watching TV, office work, slow pace walking.
Moderate intensity activities have MET from 3 to 6 and include fast walking (5 km/h), home exercises, cycling
Vigorous intensity activities have MET more than 6 and include jogging, running, vigorous home exercises like pushups, jumping etc.
PAL is also presented as a number and indicates the total energy expenditure of a specific person in relation to basal metabolic rate (BMR). “PAL = total energy expenditure divided by metabolic rate”
For example a person who is on a wheelchair and who is very inactive has PAL less than 1.4.
Office worker who does not exercise has a PAL between 1.4 and 1.69
Moderately active person who runs 1 hour per day or whose occupation involves moderate activities (example construction worker) has PAL between 1.7 and 1.99
A person who is vigorously active, for example a swimmer who trains 2 h every day or an agricultural laborer has PAL between 2.00 and 2.4.
And finally a competitive cyclist can achieve PAL higher than 2.4
Most of people having PAL between 1.4 and 1.69.
One of the ways to control weight is by improving PAL to at least 1.7 which most of the time presents a very challenging task.
Many studies were performed to exam the role of Thermic Effect of Food (TEF) in exercising.
A single session of exercises increases TEF, but the role of regular (exercise training) on TEF is not clear as some studies proved that exercise training did increase TEF; other studies failed to prove this and some observed decrease of TEF.
It is a well known factor that exercises mobilize free acids from adipose tissue.
Most probably growth hormone is responsible for this effect. It is well known that during exercising somatotropin level is increased and it remains on a higher level for many hours once the exercises have stopped.
There are also studies revealing a role of sympathetic nervous system on adipocytes. During exercises fat tissue is more sensitive to adrenaline and noradrenaline. Generally it is said that prolonged low-intensity activities have more beneficial effect on fat mobilization while high-intensity exercises burn more carbohydrates.
Regular exercises stimulate alternation in body composition by losing fat tissue and increasing muscle mass.
A role of exercises on appetite is another often studied subject. It is also a controversial matter.
A general agreement was made concluding that exercising has a mild appetite suppressant effect but mostly this applies to more intense exercises where elevated levels of catecholamines might be responsible for this outcome. Yet some authors still do not agree with these findings and believe that higher intensity exercises will only delay consuming food.
In summary it can be concluded that physical activity can positively influence management of body weight by increasing energy expenditure. Together with caloric restriction diet, regular exercises offer a decrease in body weight, change of body composition and also many important health benefits.