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.