MEASURING PHYSICAL ACTIVITY

• Reference data point shown as "10,000 STEPS" with a timestamp (35:19) on the slide; emphasis on step counts as a common metric

• Practical takeaway: $10,000$ steps per day is a commonly used target for health benefits

• Additional implied message: data collection via step counts is a standard approach in activity assessment

Data types and uses

• Minutes of activity per day (example data shown in a chart)

• Sedentary screen-based activity vs. physical activity by age group (ages 9-11? 12-14? 15-17? as per slide) – the slide shows values across age groups including 62, 62, 15-17 age group markers

• Key idea: differentiation between active time and sedentary screen time across age groups

• Purpose: illustrate how data on both physical activity and sedentary behaviour can vary by age group and time of day

Key Definitions

• Practicality (feasibility): Easy to use, cost effective

• Accuracy (validity): The degree to which the device measures what it is meant to measure correctly

• Reliability(): Consistently achieves the same results when repeated

• Social Desirability: Tendency of respondents to answer in a way viewed favourably by others

• Reactivity: When individuals change their behaviour because they know they are being monitored

• These definitions frame how different measurement tools are evaluated

Population-level assessment aims

• To provide an evidence base for behavioural determinants of health

• To understand key issues relating to physical activity and inactivity

• To track progress or lack of progress over time at a population level

• To highlight disadvantaged groups so targeted interventions can be developed

• To ensure appropriate interventions are designed, implemented, and assessed

• Emphasis: these measures inform public health planning and equity-focused interventions

Individual-level assessment aims

• To gather specific information about an individual

• To provide more accurate data for an individual so tailored strategies can be developed

• To use information as a motivational tool to increase physical activity

• To use information as a motivational tool to discourage sedentary behaviour

• To track an individual’s activity over time to identify patterns (e.g., increased sedentary time in winter) and inform targeted interventions

• Emphasis: supports personalized planning and behavior change

Subjective v. Objective Measures (definition summary)

• Subjective

  • Involves recall or memory of physical activity

  • Qualitative in nature

  • Less reliable than objective methods

  • Examples: recall surveys and diaries

• Objective

  • Direct assessment using a device or observation that provides solid data

  • Quantitative in nature

  • More reliable than subjective methods

  • Examples: pedometers, accelerometers, and observational tools

• Distinguishes how data are generated and their reliability

Subjective Methods vs Objective Methods (assessment of physical activity and sedentary behaviour methods)

• Subjective: Recall survey, Diary, Pedometer (note: pedometer is listed as subjective in this slide’s pairing), Observable tools, Digital tools, Wearable technology

• Objective: Observation, Digital tools, Wearable technology

• This slide contrasts the types of methods that fall under subjective vs objective categories

What these tools measure

• Recall survey: Frequency, Intensity

• Diaries: Frequency, Time would be captured; potentially more nuanced qualitative data

• Pedometer: Steps taken; Distance covered; Energy expenditure (estimates)

• Observational tools: Type, Time, Sedentary behaviour

• Digital tools / Wearable technology: Sedentary behaviour and Time; Sedentary behaviour is explicitly tracked

• The checkmarks indicate the dimensions each tool can capture

• Core takeaway: different tools capture different aspects (frequency, duration, intensity, type, sedentary time)

Subjective Tools

Recall Surveys (definition)

• Questionnaires asking participants to remember physical activity over a given time period

• Aims to provide basic data to assess patterns of physical activity and sedentary behaviour in large populations

• Emphasis: suited for population-level assessment due to scalability

TABLE 7.10: Advantages and disadvantages of recall surveys

• Advantages:

  • Cost-effective for large data collection

  • Easy to administer and complete; useful for large populations

  • Usable in digital or print formats

• Disadvantages:

  • Higher likelihood of lower accuracy due to poor recall and misunderstanding survey requirements

  • Social desirability bias (overreport activity, underreport sedentary behaviour)

  • Difficulty recalling details of past events, especially over longer periods

  • May be difficult for children under 10 and older adults to recall

  • Context matters when interpreting activity and sedentary behaviour

  • Does not offer real-time monitoring

Diaries (definition)

• A written record of physical activity performed

• Aims to provide detailed data for assessing physical activity and patterns in large populations

TABLE 7.11: Advantages and disadvantages of diaries

• Advantages:

  • Can record information when desired by the participant

  • Reduces the need for recall over long periods; improves accuracy

  • Easy to administer and low cost

• Disadvantages:

  • Diary burden may decrease compliance

  • Reactivity: participants may temporarily increase activity due to the recording process

  • Social desirability bias may influence entries

  • Compared with surveys, diaries have less prescriptive questions, making cross-person comparisons harder

Objective Measures

Pedometry (pedometers)

• Device records number of steps taken and estimates stride length (distance) and energy expenditure

• Worn on the hip; responds to vertical forces

• Health benefit target: Aim for 10{,}000\text{ steps/day}

• Core idea: pedometers provide an inexpensive, simple way to quantify ambulatory activity

Pedometers (TABLE 7.12): Advantages & Disadvantages

• Advantages:

  • Cheap tool (as little as a few dollars)

• Disadvantages:

  • Limited data dimensions; cannot measure intensity or context

  • Various types with different functions (steps taken, distance, energy expenditure)

  • Some can sync to digital devices; easy to use; can capture incidental activity often overlooked by surveys

  • May be inaccurate for distance when stride length changes (hills, stairs, running, sport)

  • Reactivity: wearing a pedometer can change behavior

  • Do not record sedentary behaviour

Observational Tools: Definition and scope

• Watching people’s behaviours in specific settings (e.g., PE class, lunch time)

• Can be real-time or recorded

• A trained observer records selected behaviours

• Can collect data across areas: Frequency (F), Intensity (I), Duration (D), Type (T)

Direct Observation: SOFIT

• SOFIT: System for Observing Fitness Instruction Time

• Designed to measure student physical activity, lesson context, and teacher behaviour during physical education classes

Direct observation: TABLE 7.14 Advantages and disadvantages

• Advantages:

  • Useful for assessing activity levels of children in various settings

  • Training observers increases data accuracy

• Disadvantages:

  • Time-consuming to collect and analyze data

  • Can be costly if trained professionals are required

  • Observer awareness can increase reactivity

  • Can be used with other methods (e.g., accelerometry) for better accuracy

  • Decreased accuracy with larger group sizes

Personal activity trackers & wearable devices: Description

• Use sensors: accelerometers, thermometers, ambient light sensors, UV sensors, inclinometers, optical heart rate monitors, GPS

• Can measure: Steps, Distance, Speed, Sedentary behaviour (including sleep), Energy expenditure, Intensity via heart rate

TABLE 7.15: Advantages and disadvantages of wearable devices

• Advantages:

  • Real-time data for the individual

  • Can measure physical activity and sedentary behaviour

  • Can measure any dimension (depending on device features)

  • Usable in many contexts (outdoors, water, remote locations, indoors)

• Disadvantages:

  • Can be expensive (especially advanced features)

  • Reactivity can still occur, though less than pedometers

  • Individual physiological differences can reduce accuracy

  • Some users may find it challenging to use meaningfully

Digital tools overview

• Encompass devices like tablets, computers, smartphones; use software/apps to track activity and sedentary behaviour

• Examples: Strava, MyFitnessPal, Map My Fitness, Garmin Connect

• Category: Digital Tools

TABLE 7.16: Advantages and disadvantages of digital tools

• Advantages:

  • Capable of measuring physical activity and sedentary behaviour

  • Allow in-depth data review to inform future decisions

• Disadvantages:

  • Can be expensive (especially advanced features)

  • Some users may struggle to use the technology well

  • Requires continual internet access, which may be limited in some locations

Trade-off between practicality and accuracy (conceptual slide)

• Population level measures trend toward practicality (ease of use and broad reach) with recall surveys at one end

• Objective devices (pedometers, accelerometers) trend toward higher accuracy but may have higher cost and complexity

• Visual: Population level: Recall surveys → higher practicality; Pedometers/Accelerometers → higher accuracy/precision

• Notes: “0 = objective” and “s = subjective” to indicate axis labeling in the schematic

Key concepts to remember (summary)

• Objective vs subjective measures:

  • Subjective: relies on recall/diaries/self-report; prone to recall bias and social desirability bias; provides contextual information but may be less reliable

  • Objective: uses devices or trained observers to collect quantitative data; generally more reliable and precise, but can be costly and may not capture context

• Major measurement tools and examples:

  • Recall surveys and diaries (subjective)

  • Pedometers (objective; measures steps; less reliable for distance unless stride length is known; does not measure sedentary behaviour)

  • Observational tools (SOFIT) (objective; real-time or video-based; context-rich; time-intensive)

  • Wearable devices (accelerometers, HR monitors, GPS, etc.) (objective; rich, real-time data across contexts; can be expensive; potential reactivity)

  • Digital tools (apps and platforms like Strava, MyFitnessPal, Map My Fitness, Garmin Connect) (objective or data-rich; requires internet; user engagement varies; can be costly)

• Practical vs. accuracy considerations:

  • Population-level measures prioritize practicality for large samples (often recall surveys)

  • Individual-level measures prioritize accuracy and detail (often wearables or objective monitoring)

  • The trade-off: higher practicality often comes with lower precision, while higher precision tools may be less practical for large-scale use

• Ethical and methodological considerations:

  • Social desirability bias can inflate activity reports

  • Reactivity can alter behaviour when participants know they are being measured

  • Cost and accessibility influence tool selection in different settings

• Example problem approach (Week data):

  • Sum weekly minutes per person to compare to guidelines; identify instrument type (likely diaries/recall for weekly totals); determine whether the data represent objective or subjective measurement based on the instrument used; interpret results in light of guidelines and potential accuracy limitations