Measuring PA

What aspects of PA do we measure? Timeframe – day, week, month etc. Sport and exercise vs PA Domains – Leisure time- household / gardening – Active transport- occupation FITT – Frequency- intensity – Time (duration)- type (domain)

Measurement of PA - complex Many tools available Objective and subjective measures Practicality vs accuracy trade off – With increasing accuracy of measurement comes less practicality – with more practical measures (like a survey) comes less accuracy…

Measuring POPULATIONS Predominantly self-report measures – Self report – how much PA did you do today? – Task specific diary or log – Recall surveys – Subjective measures of assessing PA levels

ADVANTAGES & DISADVANTAGES COST EFFECTIVEMEMORY / RECALL CAPABILITIES EASY TO USE IN LARGE GROUPSBIASES – SOCIAL DESIRABILITY LOW SUBJECT BURDENSENSITIVITY NON REACTIVENOT AS ACCURATE AS OBJECTIVE MEASURES PROVIDES GOOD ESTIMATE OF PA HAS POTENTIAL TO PREDICT ENERGY EXPENDITURE ASSESSES PA ACROSS MULTIPLE DOMAINS

Measuring INDIVIDUALS Behavioural observation Pedometers Accelerometers Heart rate telemetry Double labelled water GPS

Behavioural Observation Observers watch subjects & record behaviours of interest – in person or from video recording – Count people / participants – Document types, frequency & duration of PA – Assess occupational activities – Assess PA of young children – Document nature of PA in specific settings TRAINED RECORDERS – therefore objective.

ACCELEROMETERS Motion monitors or sensors Measures a range of movements Intensity of movement Amount of movment (frequency & duration) – Digitises accelerations of the body in counts per minute – Reliable and valid predictor of heart rate and energy expenditure

ACCELEROMETERS ADVANTAGES SMALL, LIGHT WEIGHT & NON INVASIVE IDEAL FOR UNDER 10 YR OLDS COMPARED TO SELF REPORT LOW SUBJECT BURDEN REAL TIME MONITORING CAN STORE LARGE AMOUNTS OF DATA FOR LONG PERIODS NON REACTIVE DISADVANTAGES EXPENSIVE ($800) CANNOT BE WORN DURING AQUATIC EVENTS NO DIFFERENTIATION OF ACTIVITY TYPE UNDER ESTIMATES MOVEMENT DURING BIKE, ROLLERBLADING, OR PREDOMINANTLY UPPER BODY ACTIVITIES ENERGY EXPENDITURE PREDICTION FORMULAS ARE BASED ON ADULT STUDIES

PEDOMETERS Step counters Detect and ‘count’ vertical accelerations Some able to calculate: – Distance walked (input stride length) – Calories expended (input weight and age)

ADVANTAGES SMALL LIGHTWEIGHT & NON INVASIVE INEXPENSIVE EASY TO ADMINISTER TO LARGE GROUPS CAN BE USED IN WIDE RANGE OF SETTINGS – SCHOOL, WORKPLACE AND COMMUNITY LOW TO MODERATE SUBJECT BURDEN INCREASES AWARENESS – GIVES IMMEDIATE FEEDBACK

DISADVANTAGES ASSESSES ONLY ONE PHYSICAL ACTIVITY BEHAVIOUR (walking or running) RELIABILITY MUST USE GOOD QUALITY MOST CANNOT RECORD FREQ OR DURATION REACTIVITY CANNOT DETECT STATIONARY ACTIVITY OR ISOMETRIC ACTIVITY ESTIMATES OF ENERGY EXPENDITURE BASED ON ADULT STUDIES.

HEART RATE MONITORING

ADVANTAGES LOW PARTICIPANT BURDEN (if worn for short amounts of time) FULL DAY STORAGE CAPACITY FOR MIN BY MIN MONITORING (freq, intensity and duration) LINEAR RELATIONSHIP B/W HR, EE AND O2 CONSUMPTION QUICK AND EASY DATA COLLECTION

DISADVANTAGES EXPENSIVE FOR LARGE GROUPS DISCOMFORT IF WORN FOR LONG TIME USEFUL ONLY FOR AEROBIC ACTIVITIES FACTORS SUCH AS AGE, BODY SIZE, PROPORTION OF MUSCLE MASS UTILISED, EMOTIONAL STRESS & CARDIOVASCULAR FITNESS ARE NOT TAKEN INTO ACCOUNT HR LAGS – IN CHANGES OF DIRECTION – THEREFORE NOT IDEAL FOR CHILDREN

DOUBLE LABELLED WATER USED TO ESTIMATE ENERGY EXPENDITURE SUBJECT IS GIVEN ISOTOPES ORALLY – THEN MONITORED VIA URINE SAMPLES VERY ACCURATE MEASURE OF EE CAN BE USED WITH ANY AGE GROUP NON INVASIVE VERY EXPENSIVE - $2000 PER PERSON