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XNN001 Methods to measure physical activity at the individual and population levels


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XNN001 Methods to measure physical activity at the individual and population levels

  1. 1. METHODS TO MEASURE PHYSICAL ACTIVITY XNN001 Population nutrition and physical activity assessment
  2. 2. Definitions of physical activity  Physical Activity is ”any bodily movement produced by skeletal muscles that results in energy expenditure”  The energy cost of physical activity may not necessarily be equivalent to body movement  Exercise is ”a specific type of PA that is planned, structured and repetitive done to improve or maintain physical fitness”  Physical fitness is ”a set of attributes either health- or performance related” and is not synonymous with physical activity
  3. 3. Why bother to measure physical activity ?  To specify which dimension of physical activity is of most importance for a particular health outcome  To make cross-cultural comparisons  To monitor temporal trends within populations  To measure the effect of interventions
  4. 4. Four parameters to describe PA  Type  The main physiological systems that are activated during the activity  Frequency  The number of times a person engages in an activity over a pre-determined period of time  Duration The temporal length of the activity  Intensity  The degree of overload an activity imposes on physiological systems in comparison to resting states
  5. 5. Validity terminology 1 Criterion validity: A questionnaire is validated against an objective method. The relationship is frequently reported as a correlation coefficient (Pearson,Spearman)
  6. 6. Validity terminology II Absolute validity: The absolute outcome (i.e. EE or time spent in activity) is compared to data from an objective instrument which provides the same outcome measure. The association is usually reported as the degree of agreement (Bland and Altman method).
  7. 7. Validity terminology III Concurrent validity: A questionnaire is compared to another self- report instrument (i.e. diary or another questionnaire). Although a high correlation between two subjective instruments suggest validity, the instruments are not of a different type and may be subject to correlated error.
  8. 8. Self-Report Methods  Questionnaires  Activity Diaries  Recall interviews
  9. 9. Questions to be asked of any questionnaire  What type of PA is it trying to assess ?  What is the frame of reference of the questionnaire ?  Is the validation sample representative of the study population?  Has the questionnaire been validated against an appropriate comparison method ?  Is the instrument reliable?
  10. 10. PAQs used in the general population  Aerobic Center Longitudinal Study PAQ  Baecke PAQ  Bouchard 3-day physical activity record  CARDIA physical activity history  Framingham Physical activity index  Godin Leisure-time exercise questionnaire  HIP activity questionnaire  Historical leisure activity questionnaire  Kuopio Ischemic Heart Disease Study Q’s  Lipid research clinics questionnaire  Minnesota Leisure-time PA  Modifiable Activity Questionnaire  Paffenbarger Physical Activity Questionnaire  Seven-Day Physical Activity Recall  Stanford Usual Activity Questionnaire  Tecumseh Occupational PAQ
  11. 11. Reliability and Validity of the International Physical Activity Questionnaire (IPAQ)  8 forms  14 centres in 12 countries  Test-retest reliability (n=2632)  Criterion validity (n=1854)  Accelerometry as comparison instrument
  12. 12. Summary; Questionnaires  Reliability; usually good to excellent  Criterion validity; poor to moderate (although significant)  Absolute validity; questionable  Questionnaires provide prevalence estimates of physical activity  Questionnaires provide the possibility to categorise respondents into activity categories  Questionnaires provide a poor measure of the absolute time spent at different intensity levels and the associated energy expenditure  Questionnaires should be used with caution in children
  13. 13. Looking for validation studies? ml
  14. 14. 7-day physical activity diary  Self completion diary  High validity  Reliability unknown
  15. 15. Stanford 7-day recall  Interviewer administered questionnaire  ~15 minutes to complete  Acceptable validity and reliability  High concurrent validity (r = 0.82 – 0.83)  High test-retest reliability (r = .31, p = .021), and very hard activities (r = .61, p = .0001)  Acceptable validity
  16. 16. Summary of subjective measures of PA  Many questionnaires available  No gold standard measure  All self-report measures associated with error  Effective indicators of which people/ sub- groups are more/ less active
  17. 17. Direct observation  Used widely among children  Children observed using specific observational system. Rating of PAL into computer/ coding form.  Number of available sustems (many validated against accelerometry, heart rate monitoring, or energy expenditure assessed by indirect calorimetry)  Fargo Activity Timesampling Survey (FATS)  Activity Patterns and Energy Expenditure (APEE)  Behaviours of eating and physical activity for children’s health evaluation system (BEACHES)  Childrens activity rating scale (CARS)  Studies of children’s activity and nutrition: Children’s activity Timesampling survey (SCAN CATS)  Level and Tempo of children’s activity LETO  System for observing play and leisure activity in youth (SOPLAY)  System for observing play and recreation in communities (SOPARC)  Observational system for recording physical activity in children – preschool version (OXRAC-P)
  18. 18. Assessment of body movement based on accelerometry Principle: Direct measure of body movement (acceleration). When a person moves, the body is accelerated in relation to the muscular forces responsible for the acceleration of the body, and in theory to EE. The acceleration can be measured in one (vertical), two (vertical + medio-lateral) or three (vertical + medio-lateral+anterior-posterior) directions.
  19. 19. Physical activity assessment by the MTI Actigraph accelerometer • Provide a detailed description of activity patterns •Excellent data storage capacity • Extensively validated • EE from complex movements are not reflected by acceleration of the body (i.e. bicycling, upper body work, walking up/down, carrying goods etc.) • Accelerometer data needs careful interpretation
  20. 20. Summary of laboratory based validation studies  Strong association (r > 0.75) between EE and activity counts in controlled settings  EE prediction equations and thus, cut-off points for different intensity levels, differ depending on the calibration activities performed and the setting of these activities  Published cut-off points are highly variable
  21. 21. Summary; Accelerometers  Extensively validated  Applicable to children and adults  Provide data on patterns of physical activity  Valid for assessing the total amount of PA  Cut-off points are arbitrary  Laboratory based EE prediction equations are not valid for free-living  Applicable in relatively large studies (n=4000)
  22. 22. Pedometers  Provide information about number of steps  Should not be used to estimate energy expenditure/ distance  Cheap, readily available  Unable to assess intensity of activity/ activities other than walking  Valid compared to accelerometers (r=0.86)  Ideally worn over 7 days but 3 sufficient
  23. 23. Heart Rate Monitoring Principle: Linear relationship between heart rate and energy expenditure during steady state work loads with large muscle groups
  24. 24. Summary; Heart Rate monitoring  Extensively validated in adults, children athletes, and obese  Applicable in relatively large studies (n = 1000)  Provide data on EE and pattern of PA  Require individual calibration  HR is affected by other factors than PA
  25. 25. The next generation of free-living physical activity assessment  Actiheart is a combined HR and movement sensor (8g, waterproof) currently being validated  It will combine the advantages of body movement and HR for prediction of PAEE during free-living conditions
  26. 26. Indirect calorimetry Measurement of the amount of heat produced by a subject by determination of the amount of oxygen consumed and the amount of carbon dioxide eliminated.
  27. 27. Doubly labeled water  Hydrogen & oxygen in water partially or completely replaced with atypical isotopes deuterium & 18O  Ingested by subject – elimination rate of deuterium isotope assessed by measuring concentration in body water over time  CO2 production measured during the interval between first and last body water samples  O2 in body water equilibrates with the body's bicarbonate and dissolved carbon dioxide pool, lost from body in CO2  Additionally lost through body water loss  Deuterium is lost only in water  deuterium change in body water over time can be used to mathematically compensate for the loss of tracer 18O to provide estimate for total carbon dioxide production  Can be used to calculate BMR
  28. 28. Room calorimetry  Energy expenditure to be calculated based on measurements of air samples  Study subject remains in closed room  Constant and measured supply of fresh air  Gas analysers attached to the unit measure oxygen consumed and carbon dioxide produced  Balance of oxygen consumed and carbon dioxide produced varies according to activity and the utilisation of different fuels by the body (carbohydrate, protein and fat).
  29. 29. Other ways to measure PA at the community/ population level Environmental  Miles of trails per capita  # of PA facilities per capita in schools  Availability of facilities to the public  # of programs for PA in community  # of agencies that sponsor PA events  Zoning regulations Behavioral Outcome Measures  Observation of usage  Membership in PA organizations (YMCA, Health clubs)  Sales of selected PA equipment, videos, etc.
  30. 30. Other ways to measure PA at the community/ population level Policy & Regulations  PE in school curriculum  Amount/% of local budget per capita devoted to physical activity/recreation  Density of recreation facilities & new construction Information  % of health-care providers that engage the public to exercise more  # of worksite materials linked to PA  % of schools offering curricula in grades k-12  # of medical reports dealing with PA  “Point of purchase” education materials on PA
  31. 31. SUMMARY  The choice of a method is a trade off between the research question, the available resources and feasibility  Valid objective methods are now available which can be used in relatively large scale epidemiological studies (n~5000)  Precise methods are needed in order to quantify dose-response relationships, gene- environment interactions, and longitudinal changes in activity patterns