Dietary assessment and physical activity measurements toolkit

Glossary of terms

 

  • Basal Metabolic Rate (BMR) – is the minimal rate of energy expenditure compatible with life. It is measured in the supine position when the individual is in a state of rest (non-sleeping), mental relaxation, fasted, and in a neutrally temperate environment. It is the largest component of total energy expenditure (TEE), typically 60-75% when measured over 24 hours. Sleeping Metabolic Rate (SMR) and Resting Metabolic Rate (RMR) are marginally different from BMR but are sometimes used in place of BMR which requires strict conditions.
  • Compendium of physical activity – was developed by Ainsworth et al (1993, 2000; MSSE) to facilitate the coding of physical activities obtained from physical activity diaries, logs, and surveys. The Compendium uses a coding scheme that links a five-digit code representing the specific activities performed in various settings with their respective metabolic equivalent (MET) intensity levels. The adult compendium contains only MET values measured in adults. Children’s games are listed in the compendium but the energy cost is based on adults performing the games. The use of adult data to assign energy costs to children's activities can be problematic as energy expenditure per unit body weight is higher in children. It decreases with age and is equivalent to adult values at approximately 18 years of age. Ridley et al (2008; Int J Behav Nutr Phys Act) have recently developed a compendium of energy costs for youth (ages 6.0–17.9 y). 
  • Metabolic Equivalent (METs) – is a widely used physiological concept that represents a simple procedure for expressing energy cost of physical activities as multiples of resting metabolic rate (RMR). One MET is defined as 1 kcal/kg/hour and is roughly equivalent to the energy cost of sitting quietly. A MET is also defined as oxygen uptake in ml/kg/min with one MET equal to the oxygen cost of sitting quietly, equivalent to 3.5 ml/kg/min. However, the adequacy of these values has been questioned (Byrne et al 2005).

METs can be used to describe energy expenditure of different physical activities (although there is no exact agreement on the borders between these levels)

  • Light-intensity activities are defined as 1.1 MET to 2.9 MET;
  • Moderate-intensity activities: 3.0 to 5.9 METs
  • Vigorous-intensity activities: 6.0 METs or more.
  • PAL (Physical Activity Level) – Total energy expenditure for 24 hours expressed as a multiple of BMR, and calculated as TEE/BMR for 24 hours. In adult men and non-pregnant, non-lactating women, BMR times PAL is equal to TEE or the daily energy requirement.
  • Physical activity (vs physical fitness) – Physical activity is not synonymous with physical fitness and may be defined as ‘any bodily movement produced by skeletal muscles that results in caloric expenditure’ (Caspersen et al, 1985; Pub Health Reports).
  • Total energy expenditure (TEE) – is the energy spent, on average, in a 24-hour period by an individual or a group of individuals. TEE consists of three components; Basal Metabolic Rate (BMR) (typically 60-75% of TEE), the thermic effect of food (10%), and energy expenditure due to physical activity (the most variable between individuals, typically 15-30% of TEE). 

Physical activity assessment methods
Objective methods

  • Accelerometery – is the most common objective method used to measure physical activity. Accelerometers are enclosed in a case and typically attached to the hip (or lower back, ankle, wrist or thigh) by a strap and provide a direct measure of acceleration of the body or segments of the body. Accelerometers attached to the waist do not capture upper body movement or cycling, and underestimate walking on an incline or carrying heavy loads.
  • Combination heart sensors – Combined heart rate and motion measurement which utilises the unique advantages of both methods (i.e. the physiological measure of heart rate by heart rate monitors and body movement measured by accelerometry) to improve estimates of physical activity e.g. the Actiheart.
  • Doubly Labelled Water (DLW) – A method used to measure the average total energy expenditure of free-living individuals over several days (usually 10 to 14), based on the disappearance of a dose of water enriched with the stable isotopes 2H and 18O. It is considered the ‘gold standard’ measure of energy expenditure but its expense limits its use in research.
  • Heart rate monitoring – is a measure of the physiological response to physical activity. Heart rate monitors are commonly worn as a chest strap which is usually wirelessly connected to a watch which captures the data.
  • Indirect calorimetry – is a method of estimating energy expenditure by measuring respiratory gases (O2 and CO2). Oxygen consumption and carbon dioxide release is measured and the Respiratory Exchange Ratio (RER) calculated to establish which type of food is being oxidized. It is assumed that each food type liberates a given amount of energy for each litre of oxygen consumed, and that the body's oxygen and carbon dioxide content remain constant. Total energy expenditure is estimated from the RER and total oxygen consumption.
  • Pedometry – Pedometers are low-cost motion sensors usually worn on a belt or waistband and provide data on steps taken by the wearer. They provide data on steps taken, and therefore, only really measure walking activity.

Self-report methods

  • Physical activity questionnaires (PAQs) - are the most widely used self-report instrument to assess physical activity and have been used extensively in research. PAQs usually provide data on the frequency, duration and intensity of physical activity in the various domains of activity i.e. house, occupation, leisure and transport.
  • Diary/log – In both diaries and logs, the 24 hour period is typically broken down into shorter segments (i.e. 15 minute segments) and individuals record their main activity for each segment. In a diary individuals are instructed to record individual bouts of activity as they occur during the day. Logs capture the time individuals spend in broad categories of activity, i.e. inactive time, sitting time, and time in light, moderate, vigorous and very rigorous intensity activity.

Others

  • Observation – has been used to assess physical activity in children. It provides detailed contextual information but intensity and energy expenditure cannot be assessed. Typically, an observer will watch children and record a rating of physical activity level using a coding form or laptop computer. A number of observational systems (e.g. Children’s Activity Rating Scale (CARS)) have been developed to assist in capturing information on children’s physical activity.  

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