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DAPA Measurement Toolkit

 

Energy expenditure

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Human consumption and expenditure of energy, alongside any change in the body’s macronutrient stores (fat, protein, and carbohydrate) is summarised by the energy balance equation:

Change in macronutrient stores = Energy consumed – Energy expended
  • The parts of the equation can be expressed as kilocalories (kcal), equivalent to 4.2 kilojoules (kJ), and are usually expressed per unit of time, for example kcal per day
  • The kJ is preferred as it is a measure of energy; however kcal (a measure of heat) is also commonly used

As depicted by Figure P.1.1, total human energy expenditure consists of the following elements:

  • Physical activity energy expenditure (PAEE), the energy expended during body movement
  • Diet-induced energy expenditure (also known as the thermic effect of food), which is associated with digestion, absorption and storage of food
  • Basal energy expenditure, which is measured in the fasted state at complete rest the morning after sleep. This is the energy required to maintain cellular function.

Resting energy expenditure, which includes sleeping energy expenditure and the energy cost of wakefulness (sometimes termed arousal), is normally slightly higher than basal metabolic energy expenditure (typically within 10%).

Resting energy expenditure is normally the largest component of daily energy expenditure, and is greater in individuals of greater mass. Physical activity energy expenditure is the most variable day-to-day and is directly related to movement. Due to their close relationship with body size, these components are typically adjusted for body mass or, more accurately, fat free mass. Resting energy expenditure is therefore commonly expressed in kcal per kilogram per hour (kcal∙kg-1∙h-1).

Figure P.1.1 Components of total energy expenditure for an average young adult woman and man.
Source: [7].
  • Physical activity is defined as any bodily movement produced by skeletal muscles resulting in energy expenditure [4]
  • Physical activity energy expenditure depends on the amount of body movement and the size of the body, since it takes more energy to move more mass
  • Total physical activity energy expenditure for a defined time-frame (be it an hour, day, week etc.) is the product of the intensity, duration and frequency of body movement
  • The rate of physical activity energy expenditure per unit time is commonly referred to as activity intensity
  • The rate of energy expenditure or intensity spectrum (see Figure P.1.2) ranges from behaviours with very low energy expenditure, such as sleep, to vigorous activities with high energy expenditure such as sprinting
  • Physical activity is the broad label that encompasses all movement of at least light intensity, and extends to movement of moderate and vigorous intensity
Figure P.1.2 The continuum of human movement and energy expenditure.
Source: [3].
  • The intensity of physical activity can be expressed relative to an individual’s resting energy expenditure, referred to as a Metabolic Equivalent Task (MET)
  • Individual activities are assigned a MET value representing their energy cost relative to this resting value
  • For example, a MET value of 2.0 represents a doubling of the resting rate of energy expenditure and would be indicative of light physical activity
  • A compendium of behaviours and their associated MET scores was originally published in 1993 [2], and updated in 2011 [1 to include 821 activities ranging from sleep (0.9 MET) to running at 14.0 mph (23.0 METs)

References

  1. Ainsworth BE, Haskell WL, Herrmann SD, Meckes N, Bassett DR, Jr., Tudor-Locke C, et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Medicine and science in sports and exercise. 2011;43(8):1575-81.
  2. Ainsworth BE, Haskell WL, Leon AS, Jacobs DR, Jr., Montoye HJ, Sallis JF, et al. Compendium of physical activities: classification of energy costs of human physical activities. Medicine and science in sports and exercise. 1993;25(1):71-80.
  3. British Heart Foundation National Centre for Physical Activity and Health. Evidence Briefing: Sedentary Behaviour2012. Available from: http://www.bhfactive.org.uk.
  4. Caspersen CJ, Powell KE, Christenson GM. Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research. Public health reports. 1985;100(2):126-31.
  5. Hall KD, Heymsfield SB, Kemnitz JW, Klein S, Schoeller DA, Speakman JR. Energy balance and its components: implications for body weight regulation. The American Journal of Clinical Nutrition. 2012;95(4):989-94.
  6. Levine JA. Measurement of energy expenditure. Public Health Nutr. 2005;8(7a):1123-32.
  7. Westerterp KR. Physical activity and physical activity induced energy expenditure in humans: measurement, determinants, and effects. Frontiers in Physiology. 2013;4:90.
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