MEASUREMENT OF ENERGY EXPENDITURE

MEASUREMENT OF ENERGY EXPENDITURE

1. a) Record of physical activity

You will be provided with an activity diary card. On this card, you will see that the day is divided into 24 x one-hour blocks with each block sub-divided into 5-minute divisions. Start the diary from the time you get up in the morning, eg if you get up at 07:30, start filling in the activities from that point in the diary and not from 00:00 at the top of the page. Each activity should be recorded to the nearest 5 minutes.

Activity codes

On the back page of the diary is a list of code letters and numbers which are to be used to code each activity. The letters refer to the most common activities, for example:

L = lying and sleeping

ST = standing

S = sitting active (eg during a lecture)

W = walking

 

Before you start, make up some code numbers to signify all other activities that you think you may carry out during the 3 day study period, for example:

1 = sitting passive (eg watching T.V.)

2 = cycling

3 = eating

4 = washing

Make sure you know what activity each code number refers to – record this information on the back page of the diary.  There may be unexpected activities that will occur during the day which you will not have coded for, for example, running for a bus.  Don’t forget to make a note of these. Try to be as accurate as you can with your recording and try not to change your activities from your normal routine as this will not then be a true representation of your 24-hour energy expenditure. If you undertake activities which take less than 5 minutes, for example going up one flight of stairs, round up the figures if it takes more than 2 minutes; you can make an adjustment next time you undertake the activity on the same day.

 

Obviously the diary must be filled with activities at the end of the 24 hours. Once the diary is completed, add up the total number of minutes attributed to each activity and record this information on the back page.  Make sure the total number of minutes adds up to 1440. Why is this?

 

  • For each activity recorded, a physical activity ratio (PAR) is required – these are on weblearn.

 

Before total energy expenditure can be calculated from the activity diaries, it is necessary to calculate basal metabolic rate

 

  1. b) Calculation of basal metabolic rate using prediction equations

In situations where BMR cannot be directly measured, an estimate can be calculated using equations. These equations rely on information such as age, gender, height and weight of individuals. The predicted values of BMR are a useful estimate of basal energy requirements for groups of healthy people.  Although they are less useful for individuals, they provide an approximate guide and will be used in this study.

 

Calculate your basal metabolic rate in MJ/day using the following THREE equations:

 

Schofield equation

Men                18-29 yr          BMR (MJ/d) = 0.063W + 2.896

30-59 yr          BMR (MJ/d) = 0.048W + 3.653

Women          18-29 yr          BMR (MJ/d) = 0.062W + 2.036

30-59 yr          BMR (MJ/d) = 0.034W + 3.538

where W = weight (kg)

 

These values are in MJ/d.

 

NB: For the diary calculations, you will need to convert this to kJ per minute (1 MJ = 1000 kJ and 1 day = 1440 minutes).

 

Harris-Benedict equation

 

BMR men = 66 + (13.7 x W) + (5 x H) – (6.8 x A)

 

BMR women = 655 + (9.6 x W) + (1.8 x H) – (4.7 x A)

 

W = weight (kg) H = height (cm) A = age (years)

 

This is in kcal/day

 

Convert your value to MJ/day (multiply by 0.004184)

Metabolic Body Size equation

BMR = 290 x W0.75

 

W = weight (kg)

 

To convert to MJ/day divide by 1000

 

 

  1. c) Calculation of energy expenditure from an activity Diary using your BMR value

 

Calculate the energy expenditure of each of your activities from your activity diary.

 

You will need the following:

The BMR (from one of the equations) in kJ/min

Time doing activity

PAR value for that activity (obtained from tables)

The following example shows how the energy expenditure cost of an activity can be calculated by combining (a) the physical activity ratio (PAR) for each of the activities recorded in the activity diary with (b) the BMR calculated from the Schofield equation:

BMR     = 5 kJ per minute

Activity   =   walking for 25 minutes (out of 1440 minutes).

PAR for walking = 2.8 (i.e. 2.8  x  BMR)

Energy cost of walking = 5  x  2.8  =  14 kJ per minute.

Total energy expended in walking  =  14   x   25   =   350 kJ.

 

The total cost of all the activities performed over the 24 h period will equal the 24 h energy expenditure. Do not add your 24 h BMR to this value as the energy cost of each activity will include this already……………………………………………………………….

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