Practical session 2 - Group 1

BODY COMPOSITION WORKSHOP

Body composition analysis can be approached from five different levels: atomic (hydrogen, carbon, oxygen and other atoms), molecular (water, lipids, proteins, carbohydrates and minerals), cellular (cells, extracellular fluids and extracellular solids), tissular (adipose tissue, skeletal muscle, bone and visceral organs) and bicompartimental (fat mass and fat-free mass).

In the last years, rapid improvements in body composition determination have been developed due to the high increase in the prevalence of obesity all over the world. The most commonly used methods for the evaluation of body composition are shown below:

1. Skinfold measurements estimate the percentage of body fat by measuring skinfold thickness at specific anatomic regions (see the picture below) using the skinfold calipers. The results of skinfold thickness are entered into an equation to estimate the percentage of body fat according to a person's age and gender. This is a non-invasive, inexpensive and easy method to estimate the body composition, but with a high inter-observer variability.

2. Biolectrical impedance is a commonly used bicompartimental method for estimating body composition based on the resistance to a small electric current through body tissues. Fat free mass is a good conductor since it contains the majority of corporal fluids and electrolytes, while fat mass is a bad one. 

3. Dual energy X-ray absorptiometry (DEXA) is a non-invasive technique based on the attenuation of two X-ray beams with different energy levels depending on the organic tissue they pass through. DEXA provides whole-body and regional estimates of bone, fat free mass and fat mass. The advantages of DEXA include a good accuracy and reproducibility. The main disadvantage of DEXA includes a small amount of radiation with this method and the underestimation of body fat in obese individuals.

4. Air displacement plethysmography (Bod-Pod®) measures the body volume by the air displaced by an individual in a sealed chamber; body volume is combined with body mass in order to determine body density. Additionally, the system discounts the pulmonary residual volume air. This non-invasive, easy, non-radiactive bicompartimental method calculates fat free mass and fat mass with excellent accuracy and reproducibility.

 

PHYSICAL ACTIVITY WORKSHOP

Two main methods for assessing physical activity levels are available:

Subjective methods: are related to your own perceptions of physical activity. They include:

• Self reports: diaries, interviews, questionnaires, logs.

• Recalls: remembering what activities you have done.

Advantages of subjective methods:

1. Suitable for small groups or individuals, as well as for population groups or subgroups.

2. Easy to complete.

3. Provides information on the context of an activity.

Disadvantages of subjective methods:

1. Heavy subject burden (entries completed throughout the day).

2. Less reliable than objective methods due to potential misinterpretation or inaccurate recording.

3. Invasion of study participant privacy.

Below you have an example of a physical activity questionnaire:

Objective methods: These methods rely on solid data and observations. They are predominately used for application in individuals and include the following:

1.- Direct observation. This method uses trained observers to systematically record physical activity behaviours of participants in a restricted environment, such as a physical education class, school playground, or in the workplace. Usually a prepared form or application is used to record the type and intensity of the activity. The biggest advantage of direct observation is that it provides more detailed information than any other methods. Moreover, trained observers also are able to evaluate physical activity more objectively than participants themselves. However, the accuracy depends on the ability of the observer.

2.- Doubly-labelled water. This method consists in a non-invasive procedure involving the intake of a quantity of water labelled with a known concentration of stable isotopes of hydrogen and oxygen. As energy is expended in the body, carbon dioxide and water are produced, and the differences between the isotope elimination rates are used to calculate total energy expenditure.

3.- Heart rate monitoring allows to measure the heart rate in real time as well as to record the heart rate for later study. The maximum heart rate (HRmax) is the highest heart rate a person can safely achieve without severe problems through exercise stress.

 

4.- Calorimetry. Direct calorimetry involves the measurement of heat produced by the body during physical activity, whereas indirect calorimetry involves the measurement of respiratory gas exchange (oxygen consumption and carbon dioxide production) during a variety of controlled conditions.

 5.- Motion sensors. Motion sensors can be divided into two main types, pedometers and accelerometers.

• Pedometers measure total physical activity by counting the number of steps an individual takes. When walking is the predominant type of activity, pedometers are quite effective as a measurement device. As much as 10,000 steps are recommended per day!

 

• Accelerometers provide more detailed information regarding intensity and direction of movement. The accelerometer monitoring system that we have used in the session with your classmates is the ActicalTM, which provides calculated energy expenditure values for energy expenditure in kilocalories and total energy expenditure in Metabolic Equivalents per Time (METs) in kilocalories/min/kg. Software reports values and average values per minute of activity count, energy expenditure and duration at each intensity level (sedentary, light, moderate and vigorous) every minute, hour, day and for total recording period.

 Below you can observe an example of the physical activity as well as the energy expenditure report of a 19-year-old male (accelerometer worn on wrist band). Studying this actigraph:

1.- How many kilocalories are consumed on Saturday September 29th?

2.- Explain the physical activity of this day.

Answers:

1.- The total energy expenditure of Saturday  September 29th is 4,247 kcal: 2,402 kcal associated to the physical activity and 1,845 kcal needed to maintain the normal body functions.

2.- The accelerometer registered an average of 212 counts, so physical activity is fine. In fact, he did 48 minutes of vigorous activity which is quite an accomplishment!

How to make a home-made accelerometer with everyday objects



Where do you have a natural accelerometer?

The inner ear consists of the cochlea, the semicircular canals and the auditory nerve. The cochlea and the semicircular canals are filled with a water-like fluid, the endolymph. The fluid and nerve cells of the semicircular canals do not participate in the task of hearing; they serve as miniature accelerometers that maintain the sense of balance by responding to gravity and changes in acceleration.

Practical session 2 - Group 2

BODY COMPOSITION WORKSHOP

Obesity is a public health problem due to its impact on morbidity and mortality, the reduction of quality of life and the health care costs. Data from the ENRICA study published in 2012 indicate that the prevalence of obesity in the adult population in Spain is 22.9% (24.4% in men and 21.4% in women). According to the World Health Organization (WHO), in 2008 approximately 1.5 billion of adults (ages 20 or +) worldwide were overweight with 500 million of them being obese:

An accurate and precise classification of overweight and obesity is required, since the consequences of overweight and obesity are more than mere aesthetic problems due to their high impact on health. Normal weight, overweight and obesity can be defined by the body mass index (BMI) and by the percentage of body fat.

Body mass index

Obesity is defined as an excess of adiposity that presents a risk to health. BMI is used in the clinical practice to evaluate the ponderal categories of the patients. The BMI (kg/m2) is calculated as a person's weight (kg) divided by the square of his/her height in metres (m). The WHO Expert Committee proposed the following BMI cutoff values for the classification of adult ponderal categories:

BMI is the most frequently used diagnostic tool for the classification of obesity, because it is an easy and reproducible measurement. In spite of its wide use for the assessment of overweight and obesity, BMI is not an accurate measurement of body fat; for example, individuals of high muscle mass will exhibit higher BMI and older adults will tend to have more body fat than younger adults for a same BMI due to skeletal muscle mass loss.

Body fat percentage

Overweight and obesity can be also assessed by using the percentage of body fat (i.e. total fat mass divided by total body mass). There is a sexual dimorphism in the percentage of body fat, with women generally having a higher percentage of body fat than men because of gender-specific fat depots in mammary glands and the gluteo-femoral region. A healthy range of body fat for women is 20-30%, whereas for men it is 10-20%. Gender-specific cutoff points for the classification of ponderal categories according to the percentage of body fat are shown below:

Practical exercise

Mary is a 25-year-old woman that practices sport daily with a BMI=26 kg/m2 and a percentage of body fat of 21%, and John is a 31-year-old man that works in an office, with a sedentary life and a BMI=26 kg/m2 and a percentage of body fat of 26%. What is their ponderal category?












Response: According to their BMI, Mary and John should be classified as overweight; however, according to their percentage of body fat (a better surrogate measurement of adiposity), Mary would be classified as normal weight, whereas John would be classified as obese. 

1. You will need to know the cutoff values for the classification of an individual as normal weight, overweight or obese according to the BMI and the percentage of body fat. There are gender-specific differences for the percentage of body fat due to the higher accumulation of fat in the mammary glands and gluteo-femoral region in women.
2. Several methods for the evaluation of body composition can be used, such as plicometry, electric bioimpedance, hydrodensitometry, air displacement plethysmography (Bod-Pod), dual energy X-ray absorptiometry (DEXA), magnetic resonance imaging and echography, among others.
3. Visceral or android obesity is associated with higher cardiovascular risk, metabolic alterations and an increase in morbi-mortality compared with subcutaneous or gynoid obesity. An easy way for the evaluation of visceral obesity in the clinical practice is the measurement of the waist circumference (cm) or the waist-to-hip ratio (WHR). You will need to know the gender-specific cutoff points of waist circumference and WHR associated with increased and substantially increased cardiometabolic risk.

PHYSICAL ACTIVITY WORKSHOP

Physical activity is defined as any body movement produced by skeletal muscles that requires energy expenditure. Although physical inactivity has been identified as the fourth risk factor for global mortality, increasing levels of physical inactivity are seen worldwide. Furthermore, sedentarism is estimated to be an important cause for the development of different types of cancers, diabetes and cardiovascular diseases. In this sense, regular and adequate levels of physical activity help to maintain a healthy body as well as to be more likely to maintain its weight.

The term physical activity should not be mistaken with exercise. Exercise is a subcategory of physical activity that is planned, structured and repetitive. Physical activity includes sports, exercise and other activities such as playing, walking, gardening, briskly pushing a baby stroller, climbing the stairs, and dancing.

 

There are some types of physical activity especially beneficial: 

1. Aerobic activities make your heart beat faster. Aerobic activities can be moderate or vigorous in their intensity.
2. Muscle-strengthening activities make your muscles stronger. These include activities like push-ups and lifting weights.
3. Bone-strengthening activities promotes bone growth and strength. These activities, like jumping, are especially important for children.
4. Balance and stretching activities enhance physical stability and flexibility. Examples are dancing, yoga or martial arts.

1. Total energy expenditure is the energy required by the organism daily and it is determined by the sum of several components: basal metabolism rate, diet-induced thermogenesis and physical activity, among others.

 

2. Physical activity represents the thermic effect of any body movement produced by skeletal muscles that requires energy expenditure. A great variability inter- and intra-individual is shown. In active individuals, the energy required for physical activity corresponds to one to two times that of the basal energy expenditure while in sedentary individuals it can represent less than half.

3. Sedentarism or physical inactivity comes up as the disease of the modern society, being identified as the fourth leading risk factor for global mortality. Sedentarism substantially increases the probability of developing obesity, cardiovascular diseases, diabetes or certain cancers.

4. Sedentarism has been positively correlated with chronic low-grade inflammation associated with obesity.

5. Different dimensions are used to describe physical activity:

• Frequency: sessions or days per week.
• Intensity: amount of effort required for the activity: low, moderate or vigorous.
• Duration: length of session or accumulated length of physical activity during a week.
• Type: other info about the nature of the activity.

6. American Heart Association recommendations for healthy adults aged 18 to 65 years:

• At least 30 minutes of moderate-intensity aerobic activity at least 5 days per week for a total of 150 minutes

      OR

• At least 25 minutes of vigorous aerobic activity at least 3 days per week for a total of 75 minutes; or a combination of the two

      AND

• Moderate to high intensity muscle-strengthening activity at least 2 or more days per week for additional health benefits.

7. The Metabolic Equivalent of Task (MET) corresponds to a physiological measure expressing the energy cost of physical activities. MET is defined as the amount of oxygen consumed while sitting at rest and is equal to 3,5 ml O2 per kg body weight per minute.

8. Two principal methods of assessing physical activity levels are described:

• Subjective methods, depending on our own perception. They are predominantly used for measurements in populations, e.g., questionnaires of physical activity, diaries, logs or recall surveys.

• The objective methods often rely on solid data or observations. These methods are predominantly used for measurements in individuals, e.g., pedometers, heart-rate telemeters, accelerometers, electronic motion sensors, calorimetry, doubly labelled water as well as direct observation.

What do the sedentarism and hibernation have in common?

Basal metabolic rate consists in the amount of energy expended daily by humans and other animals at rest. It corresponds to the minimal quantity of energy required to maintain vital physiological functions such as corporal temperature, respiration, circulation or the functioning of different organs such as liver, kidneys or brain.

Basal metabolic rate is lower in sedentary lifestyle people compared to that of active individuals. In the same way, under hibernation conditions metabolic activity declines precipitously to roughly 5% of the non-hibernating basal metabolic rate.