Measuring Physical Activity

Measurement of Physical Activity

• Physical activity is defined as any bodily movement produced by skeletal muscles resulting in energy expenditure.
• Exercise is a subset of physical activity that is planned and structured, with the goal of improving or maintaining physical fitness.
• Physical activity is classified as structured (exercise) or unstructured (lifestyle activity).

Physical Activity Domains

• Physical activity domains include leisure time, household activities, occupation, and transportation.
• Leisure time activities include running, walking and sports.
• Household activities include doing dishes and chores.
• Occupational activities include construction and being a delivery man.
• Transportation activities include bicycling to work and using public transport.

Measuring Exercise

• Exercise is usually easy to measure because it is purposeful.
• Exercise is usually performed with an underlying motivational factor, such as maintaining fitness.
• Examples of fitness types include aerobic, musculoskeletal, and skill based exercise.
• Exercise usually occurs in longer bouts, perhaps lasting 10 to 60 minutes.

Measuring Physical Activity

• Physical activity is a complex behavior that is challenging to measure in a free-living environment.
• Physical activity occurs throughout the day.
• Physical activity is accumulative and occurs in short (few seconds) and long bouts.
• Physical activity may not be easy to recall because activities are routine, mundane and/or incidental.

Kilocalories

• Energy expenditure is measured in kilocalories.
• 1 kcal represents the amount of heat required to increase the temperature of 1 kg of water by 1 degree Celsius.
• Methods to measure energy expenditure include direct and indirect calorimetry.
• In direct calorimetry, the heat in calories given off by the body is directly measured.
• Indirect calorimetry is an indirect method of measuring calories.
• Oxygen consumption is measured as an estimate of energy expenditure: Fuel + O2 -> Heat + CO2 + H2O
• There is a linear relationship between volume of oxygen (VO2) and work.

Metabolic Equivalent (MET)

• The unit of energy expenditure is the amount of oxygen used at rest, known as resting VO2.
• One MET is equal to resting VO2.
• Resting VO2 is 3.5 ml/kg/min, which is the amount of oxygen (ml) per kilogram of body weight per minute.

METs During Activity

• Running at 6mph equals 30 ml/kg/min.
• At 30 ml/kg/min, a person is using 8.6 standard METs, which is nearly 9 times greater than at rest.
• Sweeping equals 12 ml/kg/min.
• At 12 ml/kg/min, a person is using 3.4 METs, which is 3.5 times greater than at rest.

MET Tables

• MET tables give the MET value for almost all tasks.
• Physical activity intensity classification according to MET level relates to light, moderate, and vigorous activity.
• Light intensity is 1.5 – 2.9 METs.
• Moderate intensity is 3 – 6 METs.
• Vigorous intensity is 6.1 – 9 METs.
• Very vigorous intensity is > 9 METS.
• Activity that is less than 1.5 METs is now considered to be sedentary energy expenditure.
• This classification reflects the time spent in different intensity categories.

Physical Activity Assessment Techniques

• Physical activity assessment techniques can be either subjective or objective.
• Subjective techniques use self-report questionnaires.
• Objective techniques use activity monitors.
• Subjective is dependent on a person's perceptions while objective relies on solid data or observations.
• Subjective is used for measurement in populations while objective is used for measurement in small numbers of people.
• 50% of Americans meet the physical activity recommendations.

Subjective Techniques

• Subjective techniques can be administered in 2 ways: paper and pencil questionnaires or interviews (face-to-face or phone).
• Subjective techniques are easy to administer and relatively inexpensive.
• Subjective techniques can be used to assess a large sample of individuals quickly.
• Self reports and questionnaires can vary by complexity, single question to multiple components.
• The time frame of recall can include past day, past week, past month, past year, or historical/lifetime.
• Types of activities assessed include leisure, occupational, household/self care activities, and transportation.
• The Lifetime Total Physical Activity Questionnaire assesses lifetime involvement in occupational, household, and exercise/sport physical activity.
• A pro of subjective techniques is that it provides the subject of history.
• A disadvantage is that subjective techniques can be vague.
• Other cons of subjective measures can include subjectivity, precision and accuracy problems and misinterpretation of physical activity across different populations.

Objective Measures

• Objective measures are defined as measuring distance walked with step counters.
• The Ancient Romans used a 'Hodometer' of Vitruvius.
• DaVinci made step counters in 1667.
• Pedometers are simple motion sensors that can estimate habitual physical activity over a relatively long period.
• Pedometers are viewed as a motivational tool.
• Steps per day are measured (1 mile = 2000 steps).
• Referent goals for activity include <5000 steps per day is “sedentary”, 5000-7500 steps/ day is “low active”, 7500-10000 steps/day is “somewhat active", and >10000 steps/day is "active"
• The Average American takes fewer steps: Men take less than 7000 steps/day and Women take less than 5500 steps/day.
• Strengths of pedometers include that can be objective, easy to use, and easy to interpret for researchers and subjects.
• Weaknesses can include not providing information on things like intensity, steps/min, and sedentary time.
• Not all pedometers are created equal.
• Accelerometers measure body movement in terms of acceleration.
• Accelerometers use electronic sensors.
• Accelerometers store data onboard which is then downloaded to a computer at the end of a wear period.
• There are many different accelerometer monitors available, specifically multi-sensor monitors.
  • These combine many accelerometers and/or heart rate monitors.
• Strengths of accelerometers include that can be objective, easy to use, provides time stamped data on intensity of movement and hold lots of potential.
• Weaknesses can include having to deal with many monitors makes it hard to compare across studies.
• It's possible to use technology to measure 24h human behavior (duration, context and type) for things like physical activity, sitting/sedentary or sleep.
• Type of activity, social context and location can be determined.