Physical Activity Physical Activity EpidemiologyEpidemiology

Kelley K. Pettee, MSKelley K. Pettee, MS

Andrea M. Kriska, PhDAndrea M. Kriska, PhD

Caroline Richardson, MDCaroline Richardson, MD

Physical Activity Physical Activity Epidemiology Epidemiology

Definitions and Definitions and ConceptsConcepts

Physical Activity and Physical Activity and ExerciseExercise

Physical Activity

Exercise

Household Chores

Occupational Activity

Gardening/Yardwork

Total Energy ExpenditureTotal Energy Expenditure

Basal Metabolic Rate

Thermic Effect of

Food

Activities of Daily Living

Variable Activity

Tota

l E

nerg

y E

xp

en

dit

ure

Ph

ysic

al

Acti

vity

Energy BalanceEnergy Balance

Energy Intake

Energy Expenditure

Exercise vs. Lifestyle Exercise vs. Lifestyle Physical ActivityPhysical Activity

Exercise Lifestyle Physical Activity

EpidemiologyEpidemiology

The study of how a The study of how a disease or health disease or health outcome is distributed in outcome is distributed in populations and what populations and what factors influence or factors influence or determine this determine this distribution.distribution.

DefinitionsDefinitions RateRate

Measures of MorbidityMeasures of Morbidity Incidence RateIncidence Rate Prevalence RatePrevalence Rate

Measures of MortalityMeasures of Mortality Mortality RateMortality Rate

Biologic PlausibilityBiologic Plausibility ConfounderConfounder p valuep value Statistically SignificantStatistically Significant

Physical Activity Epidemiology Study Physical Activity Epidemiology Study Design Design Two Main Approaches:Two Main Approaches:

Observational Study DesignObservational Study Design

The development of disease or health outcome is The development of disease or health outcome is observed and compared between those that participate in observed and compared between those that participate in different levels of physical activitydifferent levels of physical activity

Levels of physical activity participation are self-selected by Levels of physical activity participation are self-selected by the individual and not under control of the investigator.the individual and not under control of the investigator.

Experimental Study DesignExperimental Study Design Random assignment of physical activity levels to individuals Random assignment of physical activity levels to individuals

without the disease or health outcome of interest without the disease or health outcome of interest These individuals are then followed for a period of time to These individuals are then followed for a period of time to

compare their development of the disease or health compare their development of the disease or health outcome of interestoutcome of interest

Study DesignsStudy Designs

Observation Study Design(s):Observation Study Design(s): Cross-Sectional Cross-Sectional Case-Control Case-Control ProspectiveProspective

Experimental Study Design:Experimental Study Design: Clinical TrialClinical Trial

Cross-Sectional StudyCross-Sectional Study The study population consists of individuals who do and The study population consists of individuals who do and

do not have the disease or health outcome of interest. do not have the disease or health outcome of interest. Compare the occurrence of disease or health outcome Compare the occurrence of disease or health outcome

with the level of physical activity participation.with the level of physical activity participation. Provides a snapshot of the relationship between the disease or Provides a snapshot of the relationship between the disease or

condition of interest and physical activity at condition of interest and physical activity at one point in timeone point in time..

Is there a relationship

between physical activity

participation and who does and does not

have the disease ?

HIGH

NO

Physical Activity Participation?

Individuals with Disease

Individuals

without Disease

LOW

Example of a Cross-Sectional Example of a Cross-Sectional StudyStudy What is the relationship between type 2 What is the relationship between type 2

diabetes and physical activity participation?diabetes and physical activity participation? Both diabetes status and physical activity levels Both diabetes status and physical activity levels

were determined at the same time using the were determined at the same time using the same individualssame individualsMeasurements: fasting and 2 hour post-load Measurements: fasting and 2 hour post-load plasma glucose concentrations, age, body plasma glucose concentrations, age, body mass index (BMI), waist to thigh mass index (BMI), waist to thigh circumference, and past year leisure and circumference, and past year leisure and occupational physical activityoccupational physical activity

Results: Individuals with type 2 diabetes Results: Individuals with type 2 diabetes reported being less active than those reported being less active than those without diabetes. without diabetes.

Case-Control Study Case-Control Study ((Retrospective)Retrospective) The study population consists of individuals who The study population consists of individuals who

do and do not have the disease or health outcome do and do not have the disease or health outcome Compare past physical activity participation Compare past physical activity participation

between those with and without the disease to between those with and without the disease to determine if there is a relationship.determine if there is a relationship.

PRESENT

Individuals with the disease

Individuals without

the disease

How much physical

activity did you engage

in?

PAST

Is there a difference in

physical activity levels

between those who do and do not have the disease ?

Example of a Case-Control Example of a Case-Control StudyStudy What is the relationship between lifetime What is the relationship between lifetime

physical activity and type 2 diabetes?physical activity and type 2 diabetes? Individuals, aged 37-59, with and without type Individuals, aged 37-59, with and without type

2 diabetes were asked questions about their 2 diabetes were asked questions about their physical activity levels over their lifetimephysical activity levels over their lifetime Measurements: fasting and 2 hour post-load Measurements: fasting and 2 hour post-load

plasma glucose concentrations, age, body mass plasma glucose concentrations, age, body mass index (BMI), waist to thigh circumference, and index (BMI), waist to thigh circumference, and physical activity at three points during their physical activity at three points during their lifetime as: [1. teenagers (12-18 yrs); 2. young lifetime as: [1. teenagers (12-18 yrs); 2. young adults (19-34 yrs); 3. older adults (35-49)] adults (19-34 yrs); 3. older adults (35-49)]

Results: After controlling for BMI, gender, Results: After controlling for BMI, gender, age, and waist to thigh circumference, age, and waist to thigh circumference, individuals with type 2 diabetes reported individuals with type 2 diabetes reported being less physically active over their lifetime being less physically active over their lifetime compared to individuals without diabetescompared to individuals without diabetes

Prospective Study Prospective Study (Longitudinal)(Longitudinal) The study population includes individuals who are free The study population includes individuals who are free

from the disease or health outcome. Levels of physical from the disease or health outcome. Levels of physical activity participation are assessed for a pre-determined activity participation are assessed for a pre-determined period of time. period of time.

Compare physical activity participation between those Compare physical activity participation between those who did and did not develop the disease or health who did and did not develop the disease or health outcomeoutcome

PRESENT

Individuals without the

disease. Determine

their physical activity levels

FUTURE

Individuals with disease

Individuals

without disease

Is there a difference in

physical activity

participation between

those who did and did not develop

the disease ?

Example of a Prospective Example of a Prospective StudyStudy Is there a longitudinal relationship between physical Is there a longitudinal relationship between physical

activity and the development of type 2 diabetes in a high activity and the development of type 2 diabetes in a high risk population.risk population. Subjects consisted of 1,728 Native American men and women Subjects consisted of 1,728 Native American men and women

that did not have diabetes at baseline.that did not have diabetes at baseline. Every two years, physical activity levels, diabetes status, body Every two years, physical activity levels, diabetes status, body

mass index, and various health measures were assessed.mass index, and various health measures were assessed. Individuals were followed for an average of 6 years.Individuals were followed for an average of 6 years.

Results: In the total cohort, 346 subjects developed type 2 Results: In the total cohort, 346 subjects developed type 2 diabetes. The diabetes incidence rate was lower in the diabetes. The diabetes incidence rate was lower in the more active than in the less active individuals and more active than in the less active individuals and remained after stratification by BMI [significant (p < 0.05) remained after stratification by BMI [significant (p < 0.05) in women]. in women].

This suggests that the adoption and maintenance of a This suggests that the adoption and maintenance of a physically active lifestyle can play an important role in the physically active lifestyle can play an important role in the prevention of type 2 diabetes.prevention of type 2 diabetes.

Clinical TrialClinical Trial Individuals free from the disease are randomly assigned Individuals free from the disease are randomly assigned

to either a physical activity intervention or health to either a physical activity intervention or health education group. Groups are followed for pre-education group. Groups are followed for pre-determined period of time.determined period of time.

Compare the development of disease between Compare the development of disease between individuals assigned to each group.individuals assigned to each group.

Individuals without

the Disease

FUTUREPRESENT

Physical Activity

Intervention

Health Education Group

Is there a difference in

disease development

between groups (Intervention vs.

Health Education)?

Example of a Clinical Example of a Clinical TrialTrial Can a lifestyle intervention (including diet, physical Can a lifestyle intervention (including diet, physical

activity, and weight loss) and/or drug therapy activity, and weight loss) and/or drug therapy (metformin) prevent or delay the onset of type 2 (metformin) prevent or delay the onset of type 2 diabetes in individuals with impaired glucose diabetes in individuals with impaired glucose tolerance (IGT)?tolerance (IGT)? 3,234 men and women with IGT were randomized 3,234 men and women with IGT were randomized

to one of three groups: placebo, metformin, or to one of three groups: placebo, metformin, or lifestyle modification.lifestyle modification. Lifestyle Modification Group Goals included a 7% weight Lifestyle Modification Group Goals included a 7% weight

loss and at least 150 minutes of physical activity per week. loss and at least 150 minutes of physical activity per week.

Results: Both lifestyle modification and drug therapy Results: Both lifestyle modification and drug therapy reduced the development of type 2 diabetes in high risk reduced the development of type 2 diabetes in high risk individuals when compared with the placebo group. individuals when compared with the placebo group. However, the lifestyle intervention was more effective However, the lifestyle intervention was more effective than metformin in reducing risk.than metformin in reducing risk.

Physical Activity Physical Activity AssessmentAssessment

Assessment Assessment ConsiderationsConsiderations The proper assessment or measurement of The proper assessment or measurement of

physical activity is a challenge, especially in physical activity is a challenge, especially in free-living individuals. free-living individuals.

Accurate assessments are needed to better:Accurate assessments are needed to better: Understand the specific amounts of physical Understand the specific amounts of physical

activity that are needed for health benefits.activity that are needed for health benefits. Determine if a particular behavioral Determine if a particular behavioral

intervention was successful in changing intervention was successful in changing activity behavior.activity behavior.

Considerations when determining the Considerations when determining the accuracyaccuracy of an assessment tool: of an assessment tool: ValidityValidity ReliabilityReliability Sensitivity Sensitivity

Subjective MeasuresSubjective Measures Physical Activity Questionnaires and SurveysPhysical Activity Questionnaires and Surveys

Can vary by: Can vary by: ComplexityComplexity

Self administered to interviewer administered Self administered to interviewer administered Single question to multiple componentsSingle question to multiple components

Time Frame of RecallTime Frame of Recall Past day, past week, past month, past year, Past day, past week, past month, past year, historical/lifetime historical/lifetime

Types of Activities AssessedTypes of Activities Assessed Leisure, occupational, household/self care Leisure, occupational, household/self care activities, transportationactivities, transportation

Subjective MeasuresSubjective Measures

PRO’s PRO’s NonreactiveneNonreactivene

ssss PracticalityPracticality ApplicabilityApplicability AccuracyAccuracy

CON’sCON’s Does not reflect Does not reflect

total energy total energy expenditureexpenditure

Reliability and Reliability and validity problems validity problems

Misinterpretation Misinterpretation of physical activity of physical activity across different across different populationspopulations

Objective MeasuresObjective Measures Direct ObservationDirect Observation

Classifies physical activities into Classifies physical activities into distinct categories that can be distinct categories that can be quantified and analyzed in greater quantified and analyzed in greater detail.detail. Typically used in childrenTypically used in children

Indirect CalorimetryIndirect Calorimetry Uses respiratory gas analysis to Uses respiratory gas analysis to

measure energy expenditure.measure energy expenditure. Doubly-labeled waterDoubly-labeled water

Uses biochemical markers to estimate Uses biochemical markers to estimate energy expenditureenergy expenditure

Objective MeasuresObjective Measures Heart Rate MonitorHeart Rate Monitor

Heart rate is a direct indicator of one’s Heart rate is a direct indicator of one’s physiological response to physical activityphysiological response to physical activity

Heart rate is used as an indirect estimate of Heart rate is used as an indirect estimate of energy expenditureenergy expenditure Due to linear relationship between exercise Due to linear relationship between exercise workload/intensity, heart rate, and energy workload/intensity, heart rate, and energy expenditureexpenditure

As workload/intensity increases, heart rate and As workload/intensity increases, heart rate and energy expenditure increasesenergy expenditure increases

Activity MonitorsActivity Monitors Assess the acceleration of the body in one or more Assess the acceleration of the body in one or more

planes of movementplanes of movement

Objective MonitorsObjective Monitors

PedometerPedometerRecord steps taken and Record steps taken and offer the ability to estimate offer the ability to estimate the distance walked, if the distance walked, if stride length is knownstride length is known

Physical FitnessPhysical Fitness A set of attributes that individuals have or A set of attributes that individuals have or

can achieve that relates to the ability to can achieve that relates to the ability to perform physical activity. perform physical activity.

Physical Fitness can be broken down into five Physical Fitness can be broken down into five (5) major components: (5) major components: Cardiovascular fitnessCardiovascular fitness Muscular fitnessMuscular fitness

Muscular StrengthMuscular Strength Muscular EnduranceMuscular Endurance

Body CompositionBody Composition FlexibilityFlexibility

Cardiovascular FitnessCardiovascular Fitness

Can be measured Can be measured directlydirectly using maximal exercise using maximal exercise testing (VOtesting (VO22max) or max) or indirectlyindirectly using submaximal exercise using submaximal exercise and field test protocolsand field test protocols

Maximal Oxygen Uptake (VOMaximal Oxygen Uptake (VO22 max)max) Often used as an objective measure of physical Often used as an objective measure of physical

fitnessfitness VOVO22max and Epidemiology Studiesmax and Epidemiology Studies

Time consuming Time consuming Moderate Relationship between physical activity and Moderate Relationship between physical activity and

physical fitness. physical fitness. Other factors that may influence physical activityOther factors that may influence physical activity

GeneticsGenetics GenderGender AgeAge Relative weightRelative weight

Submaximal VOSubmaximal VO22 and Field and Field TestsTests Submaximal VOSubmaximal VO22 Tests Tests

Practical option for large Epidemiological Practical option for large Epidemiological StudiesStudies

Use heart rate (HR) to predict OUse heart rate (HR) to predict O22 consumption consumption Linear relationship between HR and exercise Linear relationship between HR and exercise workload/intensityworkload/intensity

As workload/intensity increases, HR increasesAs workload/intensity increases, HR increases Field TestsField Tests

Prediction Equations to estimate VOPrediction Equations to estimate VO22 max using: max using: Distance covered in a predetermined timeDistance covered in a predetermined time Amount of time it took to cover a predetermined Amount of time it took to cover a predetermined distancedistance

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Review Questions (Developed by Review Questions (Developed by the Supercourse team)the Supercourse team)

• Is physical activity the Is physical activity the same as physical fitness?same as physical fitness?

• How much exercise is How much exercise is needed to reap the benefits of needed to reap the benefits of PA?PA?

•For what chronic diseases For what chronic diseases does PA appear to reduce does PA appear to reduce risk?risk?