CHP 11

Physical activity measurement

Assessment of the frequency, intensity, time, and/or type of physical activity an individual performs.

Why physical activity measurement is useful

Helps gather PA information, understand PA-health relationships, inform exercise prescription, and advance research, practice, and policy.

Physical activity monitoring

Observing and checking the progress or quality of physical activity over time; it is often used as an intervention tool rather than an outcome assessment.

Measurement vs. monitoring

Measurement is outcome-oriented; monitoring is process-oriented.

Physical activity as a behavior

Physical activity is complex and occurs across multiple domains.

Validity

The extent to which a tool measures what it is intended to measure; accuracy.

Reliability

The repeatability or consistency of an outcome when the same tool is used over time.

Ideal physical activity measure

A measure that is both valid (accurate) and reliable (consistent).

Subjective physical activity measure

A measure based on a person’s recall, perspective, preference, or opinion.

Objective physical activity measure

A measure based on impartial, unbiased, usually quantifiable data.

Criterion measure

A gold-standard measure used for comparison.

Self-report physical activity techniques

Diaries/logs, questionnaires, and interviews.

Advantages of self-report measures

Easy to administer and score, low cost and burden, and can assess large samples quickly.

Disadvantages of self-report measures

Social-desirability bias, memory and recall limitations, recency effects, unfamiliarity with terminology, and less accurate recall of moderate physical activity.

Recall of vigorous vs. moderate activity

People tend to recall vigorous physical activity more accurately than light or moderate activity.

Self-report diary/log

A participant records their physical activity, such as intentional exercise or activity during every 15-minute interval.

Choosing a self-report questionnaire

First identify the PA outcome you want, then choose a questionnaire that measures that outcome.

Objective physical activity techniques

Heart-rate monitors, motion sensors, pedometers, accelerometers, inclinometers, multisensors, and GPS.

Advantages of objective measures

Direct measurement of PA, multiple PA measures, continuous measurement, avoidance of most biases, and micro-level data.

Disadvantages of objective measures

Can be costly; devices and algorithms differ; may cause reactivity bias; and wear time can be interrupted.

Reactivity bias

When a person changes their behavior because they know they are being measured or observed.

Heart-rate monitor

A chest or wrist sensor that estimates physical-activity intensity, duration, and frequency.

Heart-rate monitor limitation

It does not show the type or context of PA; factors other than PA affect heart rate, and heart rate lags behind activity changes.

Pedometer

A device that measures movement during regular gait cycles.

What pedometers measure

Step counts and distance traveled.

Pedometer limitation

Accuracy can be affected at very slow or very fast walking paces.

Pedometer use

Useful for motivation and feedback.

Research-grade accelerometer

A device that measures acceleration during movement.

What research-grade accelerometers measure

Frequency, intensity, and time/duration of physical activity.

Research-grade accelerometer strengths

Provides valid and reliable micro-level data stored on the device.

Research-grade accelerometer limitations

Expensive, can cause reactivity bias, and creates researcher burden.

Commercial accelerometer

A less expensive, more stylish activity-tracking device than a research-grade accelerometer.

Commercial accelerometer capabilities

Many capture F.I.T.T.; some also include heart rate and GPS.

Commercial accelerometer limitation

Validity and reliability can vary between and within devices because of changing technology and proprietary algorithms.

Sedentary-behavior monitor

A small thigh-worn monitor that determines body posture and transitions using thigh position and acceleration.

What a sedentary-behavior monitor measures

Sitting, lying, upright posture, transitions, stepping, stepping cadence, posture time, and step counts.

Criterion physical activity techniques

Direct observation, doubly labeled water, and indirect calorimetry.

Direct observation

A trained observer records the physical activity of an individual or group.

Direct-observation strength

Provides contextual information about activity type, when and where it occurs, and with whom it occurs.

Direct-observation limitations

Requires small observation intervals, has high observer burden, and is limited to confined settings.

Doubly labeled water

A method that estimates total energy expenditure from elimination rates of oxygen and hydrogen isotopes, reflecting carbon dioxide production.

Doubly labeled water strength

Does not interfere with daily physical activity and can be used with any age group.

Doubly labeled water limitation

Does not provide F.I.T.T. information or PA context and is not a direct measure of PA energy expenditure.

Indirect calorimetry

A method that estimates energy expenditure by measuring oxygen consumption and carbon dioxide production.

F.I.T.T.

Frequency, intensity, time, and type of physical activity.

IPAQ short form

International Physical Activity Questionnaire short form; a subjective self-report measure of physical activity.

activPAL

An objective thigh-worn monitor commonly used to measure sedentary posture, transitions, and stepping.

ActiGraph

An objective accelerometer used to measure movement and physical-activity patterns.