1. Physical Activity Epidemiology
Kelley K. Pettee, MS
Andrea M. Kriska, PhD
Caroline Richardson, MD
Original Power Point file of this lecture

2. Physical Activity Epidemiology Definitions and Concepts

3. Physical Activity and Exercise
The terms physical activity and exercise were used interchangeably in the past; however, we know now that they have two distinct meanings.
Physical Activity has been defined as any bodily movement produced by skeletal muscles that results in energy expenditure (Caspersen, 1985) and includes activities of all intensities. Therefore, things such as housework, gardening, and occupational activity may all be considered types of physical activity.
Exercise is considered a subcategory of physical activity and has been defined as planned, structured, and repetitive movements which result in the improvement and/or maintenance of one or more facets of physical fitness (cardiovascular fitness, muscular strength and endurance, body composition, and/or flexibility) (Caspersen, 1985).
Therefore, all exercise is considered physical activity; however, all physical activity is not exercise. As a result, physical activity intervention efforts should focus on increasing total physical activity and not just at increasing exercise.
Recommended Reading:
Caspersen CJ, Powell KE, Christenson GM (1985). Physical activity, exercise and physical fitness: definitions and distinctions for health-related research. Public Health Reports; 100:
Household Chores
Exercise
Gardening/Yardwork
Occupational Activity

4. Total Energy Expenditure
Physical Activity
Total Energy Expenditure
Variable Activity
Activities of Daily Living
Thermic Effect of Food
Total Energy Expenditure is the total amount of energy (measured in kilocalories) that is expended over a specific time period (usually measured over a 24 hour period).
There are three major components of Total Energy Expenditure. These include: basal metabolic rate, thermic effect of food, and physical activity. The percentages provided below are estimates that are typical for a sedentary individual and these estimates will vary based on an individual’s physical activity status (active vs. inactive). For example, the contribution that physical activity makes to total energy expenditure is greater for active individuals compared to their sedentary counterparts.
Basal Metabolic Rate (~70%) kilocalories your body needs to properly function while at rest.
Thermic Effect of Food (~10%) kilocalories your body uses when it is digesting food.
Physical Activity (~20%) is the most variable component of total energy expenditure and is divided into two main components:
Activities of Daily Living such as bathing, eating, and grooming.
Variable Activity such as sports, leisure, and occupational physical activity.
Recommended Reading:
Ravussin E and Bogardus C (1992). A brief overview of human energy metabolism and its relationship to essential obesity. American Journal of Clinical Nutrition, 55: S242-S245.
Basal Metabolic Rate

5. Energy Balance Energy Expenditure Energy Intake
Ensuring optimal health and maintaining a healthy body weight is accomplished through sound dietary practices and participation in regular amounts of physical activity.
Energy Balance is the difference between the number of kilocalories that you eat (energy intake) and the number of kilocalories that you burn (energy expenditure).
If energy intake is greater than energy expenditure than you are said to be in positive energy balance. An individual in positive energy balance will gain weight.
If energy intake is less than the amount of energy that is expended than you are said to be in negative energy balance. An individual in negative energy balance will loss weight.
If energy intake is equal to the amount of energy that is expended than an individual will maintain his/her weight.

6. Exercise vs. Lifestyle Physical Activity
The term structured physical activity is simply what comes to mind when we think of exercise. It consists of planned bouts of physical activity and is often times more straightforward to describe, in terms of intensity, time, and/or frequency than unstructured physical activity.
Lifestyle physical activities are bouts of physical activity that are incorporated into an individual’s everyday routine. Lifestyle physical activities are often considered unstructured because they vary based on events and/or situations that develop over the course of a given day. A few examples of lifestyle physical activities include taking the stairs instead of the elevator or escalator, parking the car further away in store parking lots, walking around the home or office while chatting on a cordless telephone, etc.
Similar to structured physical activity, maintaining an “active head”, by making “active” lifestyle choices where possible will also help improve one’s health.
Exercise
Lifestyle Physical Activity

7. Epidemiology
The study of how a disease or health outcome is distributed in populations and what factors influence or determine this distribution.
There are two fundamental assumptions in epidemiology:
Human disease is not random
Human disease has causal and preventative factors that can be identified through scientific investigation of different populations or subgroups of individuals within a population (Hennekens, 1987).
The primary goal of epidemiology is to identify the determinants of health and disease to decrease mortality (death) and morbidity (a diseased condition or state) within a population (Kuller, 1987). Physical Activity Epidemiology, therefore, focuses on physical activity within populations and investigates how physical activity levels impact health and disease to decrease mortality and morbidity. Physical Activity Epidemiology typically incorporates both the assessment of physical activity, as well as, intervention efforts focusing on increasing physical activity.
Recommended Readings:
Gordis L (2000). Epidemiology (2nd ed.). Philadelphia, PA: W.B. Saunders Company.
Hennekens CH, Buring JE (1987). Epidemiology in medicine. Boston: Little, Brown: 3-15.
Kuller LH (1987). Relationship between acute and chronic disease epidemiology. Yale Journal of Biology and Medicine; 60:

8. Definitions Rate Biologic Plausibility Confounder p value
Measures of Morbidity
Incidence Rate
Prevalence Rate
Measures of Mortality
Mortality Rate
Biologic Plausibility
Confounder
p value
Statistically Significant
Rate is how fast a disease or condition is occurring in a population.
Measures of Morbidity
Incidence is the number of new cases of a particular disease that occurs during a specified period of time divided by the number of persons in the population that is at risk for developing the disease.
Prevalence is the number of affected persons present in the population at a specific time divided by the number of persons in the population at that time.
Measures of Mortality
Mortality Rate is the number of deaths at a specific time divided by the number of persons in the population at that time.
Biologic Plausibility is a theory, based on existing medical literature, that supports the relationship or causal link between physical activity and a particular disease or health outcome.
A confounder is a variable with an effect that is entangled with the effect of physical activity which cannot be easily separated and studied independently. Confounders need to be controlled for using statistical procedures to ensure accurate results. For a variable to be considered a confounder in physical activity epidemiology, it has to be related to both physical activity and the disease and/or health outcome of interest. Confounders in physical activity epidemiology include: age, BMI, and baseline health status. For example, when looking at the relationship between inactivity and physical inactivity, age may be a confounder because both heart disease risk and physical inactivity increases as one ages. In this case, it may be hard to determine if age or physical inactivity lead to the development of heart disease.
p value is used to quantify the degree to which chance may account for an association that was observed in a particular study. Using statistical procedures, researchers decide whether an association between a disease or health outcome and physical inactivity is statistically significant. The p value allows researchers to quantify the probability or likelihood that the association could have occurred by chance alone.
Recommended Readings:
Gordis L (2000). Epidemiology (2nd ed.). Philadelphia, PA: W.B. Saunders Company.

9. Physical Activity Epidemiology Study Design Two Main Approaches:
Observational Study Design
The development of disease or health outcome is observed and compared between those that participate in different levels of physical activity
Levels of physical activity participation are self-selected by the individual and not under control of the investigator.
Experimental Study Design
Random assignment of physical activity levels to individuals without the disease or health outcome of interest
These individuals are then followed for a period of time to compare their development of the disease or health outcome of interest
There are two main approaches that investigators can use to determine if physical inactivity plays a role in the development of a specific disease or condition.
In the observational study design, levels of physical activity participation are self-selected by the participant. Typically, individuals will differ by characteristics (confounders), other than physical activity participation, that may influence the disease or outcome of interest.
Of the two main approaches, the experimental study design is more powerful and conclusive than the observational study design. It is more conclusive because the levels of physical activity are not self-selected by the participant. Individuals are randomly assigned to a group that is encouraged to participate in physical activity or to a reference group. All study participants are followed for a period of time and development of disease or health outcome is compared between groups.
Random assignment or randomization implies that each individual has the same chance of being in any of the available study groups. The randomization process removes any potential clinician and/or patient biases about who receives the physical activity intervention. Also, randomization ensures equal distribution of potential confounding variables (age, body mass index, etc.) among exposure groups. The equal distribution of confounding variables will lead to a clearer picture of the association between physical activity and the disease or health outcome of interest.
Recommended Readings:
Kriska AM, FitzGerald SJ, Pereira MA (2001). Physical activity epidemiology. In: S Brown, Introduction to exercise science. Philadelphia, PA: Lippincott Williams & Wilkins:
Friis RH, Sellers TA (1996). Epidemiology for Public Health Practice. Gaithersberg, MD: Aspen Publishers: 271.

10. Study Designs Observation Study Design(s): Experimental Study Design:
Cross-Sectional
Case-Control
Prospective
Experimental Study Design:
Clinical Trial
The following slides will discuss, in greater detail, both observational and experimental study designs. Observational study designs include: cross-sectional, case-control, and prospective studies. The clinical trial is an example of an experimental study design.

11. Cross-Sectional Study
The study population consists of individuals who do and do not have the disease or health outcome of interest.
Compare the occurrence of disease or health outcome with the level of physical activity participation.
Provides a snapshot of the relationship between the disease or condition of interest and physical activity at one point in time.
Is there a relationship between physical activity participation and who does and does not have the disease ?
Individuals with Disease
HIGH
A cross-sectional study provides an instantaneous picture of the relationship between the disease or condition of interest and physical activity levels at one point in time.
PROS:
Quick
Easy
Cheap
CONS:
An association does not prove causality. Therefore, with this study design, we cannot get information about whether physical inactivity caused the disease or the disease caused the physical inactivity.
It is not possible to assess what effect changing the level of physical activity participation would have on the disease or condition of interest.
Recommended Reading:
Gordis L (2000). Epidemiology (2nd ed.). Philadelphia, PA: W.B. Saunders Company.
LOW
Individuals without Disease NO
Physical Activity Participation?

12. Example of a Cross-Sectional Study
What is the relationship between type 2 diabetes and physical activity participation?
Both diabetes status and physical activity levels were determined at the same time using the same individuals
Measurements: fasting and 2 hour post-load plasma glucose concentrations, age, body mass index (BMI), waist to thigh circumference, and past year leisure and occupational physical activity
Results: Individuals with type 2 diabetes reported being less active than those without diabetes.
Recommended Reading:
Kriska AM., LaPorte RE, Pettitt DJ, Charles MA, Nelson RG, Kuller LH, Bennett PH., Knowler WC (1993). The association of physical activity with obesity, fat distribution and glucose intolerance in Pima Indians. Diabetologia, 36:863-9.

13. Case-Control Study (Retrospective)
The study population consists of individuals who do and do not have the disease or health outcome
Compare past physical activity participation between those with and without the disease to determine if there is a relationship.
Individuals with the disease
Is there a difference in physical activity levels between those who do and do not have the disease ?
How much physical activity did you engage in?
PROS:
Quick
Cheap
Good for studying rare diseases or health outcome because the investigators don’t have to wait for individuals to develop the disease or health outcome of interest because they begin the study with diseased and non-diseased individuals.
CONS:
It is difficult for investigators to determine how long it took to develop the disease or health outcome because they began with individuals that either had or did not have the disease.
Subject to recall bias because a diseased or high risk individual may remember past events differently than healthy individuals.
Recommended Reading:
Gordis L (2000). Epidemiology (2nd ed.). Philadelphia, PA: W.B. Saunders Company.
Individuals without the disease
PAST
PRESENT

14. Example of a Case-Control Study
What is the relationship between lifetime physical activity and type 2 diabetes?
Individuals, aged 37-59, with and without type 2 diabetes were asked questions about their physical activity levels over their lifetime
Measurements: fasting and 2 hour post-load plasma glucose concentrations, age, body mass index (BMI), waist to thigh circumference, and physical activity at three points during their lifetime as: [1. teenagers (12-18 yrs); 2. young adults (19-34 yrs); older adults (35-49)]
Results: After controlling for BMI, gender, age, and waist to thigh circumference, individuals with type 2 diabetes reported being less physically active over their lifetime compared to individuals without diabetes
Recommended Reading:
Kriska AM., LaPorte RE, Pettitt DJ, Charles MA, Nelson RG, Kuller LH, Bennett PH., Knowler WC (1993). The association of physical activity with obesity, fat distribution and glucose intolerance in Pima Indians. Diabetologia, 36:863-9.

15. Prospective Study (Longitudinal)
The study population includes individuals who are free from the disease or health outcome. Levels of physical activity participation are assessed for a pre-determined period of time.
Compare physical activity participation between those who did and did not develop the disease or health outcome
Is there a difference in physical activity participation between those who did and did not develop the disease ?
Individuals with disease
Individuals without the disease. Determine their physical activity levels
PROS:
Can establish cause and effect. Through the use of this study design, investigators are able to determine if physical inactivity lead to the disease or health outcome of interest.
Can directly measure the development of disease or condition of interest in both those who do and do not participate in physical activity.
CONS:
Not a good study design for studying rare diseases or conditions because the investigators have to wait for individuals to develop the disease or condition of interest.
Can be costly and time-consuming
Often requires a large sample size to ensure that enough study participants will develop the disease or outcome of interest during the course of the study.
This study design is subject to participants dropping out or being loss to follow-up (can’t be found) because of the lengthy study time.
Recommended Reading:
Gordis L (2000). Epidemiology (2nd ed.). Philadelphia, PA: W.B. Saunders Company.
Individuals without disease
PRESENT
FUTURE

16. Example of a Prospective Study
Is there a longitudinal relationship between physical activity and the development of type 2 diabetes in a high risk population.
Subjects consisted of 1,728 Native American men and women that did not have diabetes at baseline.
Every two years, physical activity levels, diabetes status, body mass index, and various health measures were assessed.
Individuals were followed for an average of 6 years.
Results: In the total cohort, 346 subjects developed type 2 diabetes. The diabetes incidence rate was lower in the more active than in the less active individuals and remained after stratification by BMI [significant (p < 0.05) in women].
This suggests that the adoption and maintenance of a physically active lifestyle can play an important role in the prevention of type 2 diabetes.
Recommended Reading:
Kriska AM, Saremi A, Hanson RL, Bennett PH, Kobes S, Williams DE, Knowler WC (2003). Physical activity, obesity, and the incidence of type 2 diabetes in a high-risk population. American Journal of Epidemiology; 158:

17. Clinical Trial
Individuals free from the disease are randomly assigned to either a physical activity intervention or health education group. Groups are followed for pre-determined period of time.
Compare the development of disease between individuals assigned to each group.
Physical Activity Intervention
Is there a difference in disease development between groups (Intervention vs. Health Education)?
Individuals without the Disease
In a clinical trial, individuals free from disease are randomly assigned to receive either a physical activity intervention or no intervention (the health education group). The two groups are followed for a period of time to determine if they differ. This difference in groups is typically revealed by the percent of people that develop the disease or health outcome of interest.
PROS:
Random assignment of who does and does not receive the physical activity intervention minimizes potential biases.
Data generated is prospective in nature and better than retrospectively obtained data which can be subject to participant recall bias.
Just like the prospective design, a clinical trial can establish cause and effect. Investigators will be able to determine if physical inactivity lead to the disease or health outcome of interest.
CONS:
Expensive
Not suitable for study of physical activity interventions to prevent diseases or outcomes that take a long time to develop or are rare.
Individuals may behavior differently if they know they are being watched.
This study is subject to participant dropout and loss to follow-up.
Recommended Reading:
Gordis L (2000). Epidemiology (2nd ed.). Philadelphia, PA: W.B. Saunders Company.
Health Education Group
PRESENT
FUTURE

18. Example of a Clinical Trial
Can a lifestyle intervention (including diet, physical activity, and weight loss) and/or drug therapy (metformin) prevent or delay the onset of type 2 diabetes in individuals with impaired glucose tolerance (IGT)?
3,234 men and women with IGT were randomized to one of three groups: placebo, metformin, or lifestyle modification.
Lifestyle Modification Group Goals included a 7% weight loss and at least 150 minutes of physical activity per week.
Results: Both lifestyle modification and drug therapy reduced the development of type 2 diabetes in high risk individuals when compared with the placebo group. However, the lifestyle intervention was more effective than metformin in reducing risk.
Recommended Reading:
The Diabetes Prevention Program Research Group (2002). Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin. The New England Journal of Medicine, 346:
The Diabetes Prevention Program Research Group (2002). The Diabetes Prevention Program: Description of the Lifestyle Intervention Program. Diabetes Care; 25:

19. Physical Activity Assessment

20. Assessment Considerations
The proper assessment or measurement of physical activity is a challenge, especially in free-living individuals.
Accurate assessments are needed to better:
Understand the specific amounts of physical activity that are needed for health benefits.
Determine if a particular behavioral intervention was successful in changing activity behavior.
Considerations when determining the accuracy of an assessment tool:
Validity
Reliability
Sensitivity
The assessment tool must elicit accurate information on the types of physical activities that encompass the greatest proportion of energy expenditure in the study population. If not, the assessment tool will fall short and lead to an inaccurate assessment.
Accuracy is the degree to which an assessment tool is able to measure physical activity and/or exercise. Accuracy is comprised of both validity and reliability.
Validity is the degree to which an instrument measures what it sets out to measure.
Reliability of an assessment tool relates to it’s repeatability. Will the results that were obtained with a particular assessment tool be replicated if the test is repeated?
Sensitivity relates to the ability of an assessment tool to accurately measure and detect change in physical activity patterns.
Recommended Reading:
Welk GJ (2002). Physical activity assessments for health-related research. Champaign, IL: Human Kinetics.

21. Subjective Measures Physical Activity Questionnaires and Surveys
Can vary by:
Complexity
Self administered to interviewer administered
Single question to multiple components
Time Frame of Recall
Past day, past week, past month, past year, historical/lifetime
Types of Activities Assessed
Leisure, occupational, household/self care activities, transportation
Questionnaires and Surveys are subjective instruments used in epidemiological research to quantify physical activity. Physical activity questionnaires/surveys can vary by complexity, time frame or recall, and types of activities surveyed.
Complexity. Physical activity questionnaires can vary in complexity by the manner in which it is administered (self vs. interviewer). They can also vary from the use of a single question to more complex questionnaires that attempt to survey a wide range of popular activities over a predetermined period of time.
Time Frame of Recall. Questionnaires/surveys may inquire about usual activity done within the past day, past week, past month, past year, or even over one’s entire lifetime.
Types of Activities. Early studies in physical activity epidemiology estimated one’s physical activity based on the activities that were performed at work. However, as a country becomes more industrialized, the amount of physical activity accumulated on the job and/or as a means of transportation declines. As a result, investigators shifted towards questionnaires and surveys that measured only leisure-time physical activity. In addition, for older or diseased populations the assessment of lower intensity activities, such as household or activities of daily living may be necessary when determining one’s physical activity status. Subjective measures are less likely to capture lower intensity activities because it is often difficult to accurately recall lower intensity types of physical activity such as housework and childcare. For accurate assessment of low intensity activity, objective measures are needed.
Recommended Readings:
Kriska AM and Caspersen CJ (1997). Introduction to the Collection of Physical Activity Questionnaires in A Collection of Physical Activity Questionnaires for Health-Related Research. Centers for Disease Control and Prevention. Medicine and Science in Sports and Exercise, 29 [Supplement].

22. Subjective Measures PRO’s CON’s Nonreactiveness Practicality
Applicability
Accuracy
CON’s
Does not reflect total energy expenditure
Reliability and validity problems
Misinterpretation of physical activity across different populations
PROS of the questionnaire/survey include their nonreactiveness. The individual’s behavior will usually not change as a direct result of the assessment technique. Also, questionnaires/surveys are practical because they are low in cost and relatively convenient to the participant. Another benefit of the questionnaire/survey is it’s applicability and ability to be modified to suit the population of interest. Finally, questionnaires/surveys have acceptable accuracy (both reliability and validity) in situations where the investigator is trying to measure differences in physical activity levels between groups.
CONS. Physical activity levels obtained from questionnaires do not reflect total energy expenditure for a particular individual because they do not consider the energy requirements of such things as basal metabolic rate, thermic effect of food, and in most cases, activities of daily living (lower intensity activities). There may be assessment issues surrounding an individual’s inability to accurately recall activity. Different populations may interpret physical activity in different ways or participate in different types of activities; therefore, the subjective measure should be modifiable to fit the needs and interests of the population.
Recommended Readings:
Kriska AM and Caspersen CJ (1997). Introduction to the Collection of Physical Activity Questionnaires in A Collection of Physical Activity Questionnaires for Health-Related Research. Centers for Disease Control and Prevention. Medicine and Science in Sports and Exercise, 29 [Supplement].
Welk GJ (2002). Physical activity assessments for health-related research. Champaign, IL: Human Kinetics.

23. Objective Measures Direct Observation Indirect Calorimetry
Classifies physical activities into distinct categories that can be quantified and analyzed in greater detail.
Typically used in children
Indirect Calorimetry
Uses respiratory gas analysis to measure energy expenditure.
Doubly-labeled water
Uses biochemical markers to estimate energy expenditure
Direct Observation not only measures physical activity, but also identifies the type and specifics (when, where, and with whom) of the activity. In recent years, it has been mainly used in children. PROS. Direct observation provides both quantitative and qualitative information on an individual’s physical activity. Also, physical activity behaviors can be specifically targeted due to the fact that physical activity categories are established a priori. CONS. Direct observation involves a time and labor-intensive data collection; therefore, it may not be feasible for use in large epidemiological studies. Also, the observer’s presence may alter the participant’s normal physical activity patterns. Finally, there is limited research regarding the validation of direct observation against physiological criteria.
Indirect Calorimetry measures oxygen consumption and carbon dioxide production over short or long periods of time. For short durations, participants wear a face mask during rest and/or exercise. For longer durations, individuals are confined to a metabolic chamber.
Doubly-Labeled Water is a biochemical procedure that estimates energy expenditure through the use of markers that reflect the rate of metabolism in the body. During the procedure, two stable isotopes of water are ingested by the study subject. After a 1 to 2 week period, investigators determine how quickly the body lost the water isotopes. The water isotopes can be lost through urine, sweat, and/or evaporation. The investigators measure the difference between the rate of loss of the two water isotopes to determine energy expenditure. PROS. Indirect calorimetry and doubly-labeled water are precise and accurate measures of total energy expenditure. CONS. Both indirect calorimetry and doubly-labeled water have high participant burden and both measures are costly; therefore, may not be feasible in large epidemiological studies.
Recommended Reading:
Welk GJ (2002). Physical activity assessments for health-related research. Champaign, IL: Human Kinetics.

24. Objective Measures Heart Rate Monitor Activity Monitors
Heart rate is a direct indicator of one’s physiological response to physical activity
Heart rate is used as an indirect estimate of energy expenditure
Due to linear relationship between exercise workload/intensity, heart rate, and energy expenditure
As workload/intensity increases, heart rate and energy expenditure increases
Activity Monitors
Assess the acceleration of the body in one or more planes of movement
Heart Rate Monitors are used to assess heart rate response. PROS. Heart rate monitoring is valid in both laboratory and field settings. Also, there is low participant burden for short monitoring periods. Heart rate monitoring is able to provide information relating to workload/intensity, frequency, and duration of physical activity for adult populations. It is an easy and quick method making it practical for large studies. CONS. Heart rate monitoring can be expensive, there may be possible patient discomfort if the monitoring period is lengthy, and it is only useful for aerobic (cardiovascular) activities. Finally, characteristics of heart rate, especially among trained individuals, may affect the relationship between heart rate and energy expenditure and may lead to inaccurate results.
Activity Monitors, often referred to as accelerometers, assess the acceleration of the body in a specific dimension (uniaxial) or multiple dimensions (triaxial). The monitors provide information on the intensity of acceleration at specified intervals. Following data collection, this information is downloaded to a computer for data processing. PROS. Objective measure of body movement that has been found to be valid in both laboratory and free-living settings. Activity monitors have the ability to provide information relating to intensity, frequency, and duration of physical activity. They are also non-invasive and have the ability to record over extended periods of time. CONS. They are costly and do not provide information concerning activity type. Also, the uniaxial monitors may be inaccurate during upper-body movements and during bicycling. Most activity monitors are not waterproof; therefore, water-based activities cannot be assessed. Also, improper monitor placement may lead to inaccurate results.
Recommended Reading:
Welk GJ (2002). Physical activity assessments for health-related research. Champaign, IL: Human Kinetics.

25. Objective Monitors Pedometer
Record steps taken and offer the ability to estimate the distance walked, if stride length is known
The pedometer is another type of movement monitor that counts steps taken throughout the day (walking, jogging, running). PROS. Pedometers are objective measure of walking, a common type of physical activity. Pedometers are inexpensive, non-invasive, and easy to administer, making them practical to use in a variety of settings. Pedometer step count feedback can be used to promote behavior change. CONS. Pedometers were specifically designed to assess ambulatory movement and are not accurate in assessing activities that move away from ambulation (ex. bicycling). Also, most pedometers are not waterproof and cannot be used to assess water-based activities. Proper placement is essential for accurate results and pedometers may be subject to patient tampering.
Recommended Reading:
Crouter SE, Schneider PL, Karabulut M, Bassett DR Jr (2003). Validity of 10 electronic pedometers for measuring steps, distance, and energy cost Medicine & Science in Sports & Exercise; 35:
Schneider PL, Crouter SE, Bassett DR (2004). Pedometer measures of free-living physical activity: comparison of 13 models. Medicine & Science in Sports & Exercise; 36 :

26. Physical Fitness
A set of attributes that individuals have or can achieve that relates to the ability to perform physical activity.
Physical Fitness can be broken down into five (5) major components:
Cardiovascular fitness
Muscular fitness
Muscular Strength
Muscular Endurance
Body Composition
Flexibility
The measurement of physical fitness is common practice in both preventative and rehabilitative exercise programs. The purpose of fitness testing includes: educating individuals about current fitness status relative to population norms, collecting baseline and follow-up data to measure progress in an exercise program, motivation of exercise participants, and risk stratification for chronic disease development. Cardiovascular fitness will be emphasized in this lecture.
Recommended Reading:
American College of Sports Medicine (2000). ACSM’s guidelines for exercise testing and prescription (6th ed.). Baltimore, MD: Lippincott Williams & Wilkins.

27. Cardiovascular Fitness
Can be measured directly using maximal exercise testing (VO2max) or indirectly using submaximal exercise and field test protocols
Recommended Reading:
American College of Sports Medicine (2000). ACSM’s guidelines for exercise testing and prescription (6th ed.). Baltimore, MD: Lippincott Williams & Wilkins.

28. Maximal Oxygen Uptake (VO2 max)
Often used as an objective measure of physical fitness
VO2max and Epidemiology Studies
Time consuming
Moderate Relationship between physical activity and physical fitness.
Other factors that may influence physical activity
Genetics
Gender
Age
Relative weight
Because physical activity is difficult to measure, Maximal Oxygen Uptake or VO2 max is often used as a proxy measure of physical activity. However, VO2 max is actually a measure of physical fitness, not physical activity.  Those who are more active and expend more energy tend to have higher fitness levels.  Many VO2 max protocols are time consuming and may not be possible in large epidemiological studies where there are great number of participants.   In addition, when examining population studies, there is only a moderate relationship between physical activity and physical fitness (Siconolfi, 1985; Jacobs, 1993).  This lack of a strong relationship could be due to the fact that there are other factors besides activity, such as genetics (Bouchard, 1988), gender, age, and relative weight (Leon, 1981) that influence physical activity. 
Recommended Readings:
Siconolfi SF, Lasater TM, Snow RCK, Carleton RA (1985). Self-reported physical activity compared with maximal oxygen uptake. American Journal of Epidemiology; 122:
Jacobs DR, Ainsworth BE, Hartman TJ, Leon AS (1993). A simultaneous evaluation of 10 commonly used physical activity questionnaires. Medicine and Science in Sport and Exercise; 25:
Bouchard C, Boulay MR, Simoneau JA, Lortie G, Perusse L (1988). Heredity and trainability of aerobic and anaerobic performance: an update. Sports Medicine; 5:
Leon AS, Jacobs DR, DeBacker G, Taylor HL (1981). Relationship of physical characteristics and life habits to treadmill exercise capacity.  American Journal of Epidemiology; 113:
American College of Sports Medicine (2000). ACSM’s guidelines for exercise testing and prescription (6th ed.). Baltimore, MD: Lippincott Williams & Wilkins.

29. Submaximal VO2 and Field Tests
Submaximal VO2 Tests
Practical option for large Epidemiological Studies
Use heart rate (HR) to predict O2 consumption
Linear relationship between HR and exercise workload/intensity
As workload/intensity increases, HR increases
Field Tests
Prediction Equations to estimate VO2 max using:
Distance covered in a predetermined time
Amount of time it took to cover a predetermined distance
In instances where VO2 max testing is not practical, such as with large epidemiological studies, submax VO2 and field tests have been used to estimate VO2 max. Submax VO2 tests use heart rate to predict the oxygen consumption that would have occurred during maximal workloads (VO2 max). Submax VO2 tests are able to predict VO2 max because of the linear relationship that exists between heart rate and exercise workload/intensity (as workland/intensity increases; HR increases) (ACSM, 2000).
Similarly, field tests use either the distance that is covered or the amount of time it took to cover a particular distance to estimate VO2 max using established prediction equations (ACSM, 2000)
Recommended Readings:
American College of Sports Medicine (2000). ACSM’s guidelines for exercise testing and prescription (6th ed.). Baltimore, MD: Lippincott Williams & Wilkins.

30. References
American College of Sports Medicine (2000). ACSM’s guidelines for exercise testing and prescription (6th ed.). Baltimore, MD: Lippincott Williams & Wilkins.
Bouchard C, Boulay MR, Simoneau JA, Lortie G, Perusse L (1988). Heredity and trainability of aerobic and anaerobic performance: an update. Sports Medicine; 5:
Caspersen CJ, Powell KE, Christenson GM (1985). Physical activity, exercise and physical fitness: definitions and distinctions for health-related research. Public Health Reports; 100:
Crouter SE, Schneider PL, Karabulut M, Bassett DR Jr (2003). Validity of 10 electronic pedometers for measuring steps, distance, and energy cost Medicine & Science in Sports & Exercise; 35:

31. References
The Diabetes Prevention Program Research Group (2002). Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin. The New England Journal of Medicine, 346:
The Diabetes Prevention Program Research Group (2002). The Diabetes Prevention Program: Description of the Lifestyle Intervention Program. Diabetes Care; 25:
Friis RH, Sellers TA (1996). Epidemiology for Public Health Practice. Gaithersberg, MD: Aspen Publishers: 271.
Gordis L (2000). Epidemiology (2nd ed.). Philadelphia, PA: W.B. Saunders Company.

32. References
Jacobs DR, Ainsworth BE, Hartman TJ, Leon AS (1993). A simultaneous evaluation of 10 commonly used physical activity questionnaires. Medicine and Science in Sport and Exercise; 25:
Hennekens CH, Buring JE (1987). Epidemiology in medicine. Boston: Little, Brown: 3-15.
Kriska AM and Caspersen CJ (1997). Introduction to the Collection of Physical Activity Questionnaires in A Collection of Physical Activity Questionnaires for Health-Related Research. Centers for Disease Control and Prevention. Medicine and Science in Sports and Exercise, 29 [Supplement].
Kriska AM, FitzGerald SJ, Pereira MA (2001). Physical activity epidemiology. In: S Brown, Introduction to exercise science. Philadelphia, PA: Lippincott Williams & Wilkins:

33. References
Kriska AM., LaPorte RE, Pettitt DJ, Charles MA, Nelson RG, Kuller LH, Bennett PH., Knowler WC (1993). The association of physical activity with obesity, fat distribution and glucose intolerance in Pima Indians. Diabetologia, 36:863-9.
Kriska AM, Saremi A, Hanson RL, Bennett PH, Kobes S, Williams DE, Knowler WC (2003). Physical activity, obesity, and the incidence of type 2 diabetes in a high-risk population. American Journal of Epidemiology; 158:
Kuller LH. Relationship between acute and chronic disease epidemiology. Yale Journal of Biology and Medicine; 60:
Leon AS, Jacobs DR, DeBacker G, Taylor HL (1981). Relationship of physical characteristics and life habits to treadmill exercise capacity. American Journal of Epidemiology; 113:

34. References
Ravussin E and Bogardus C (1992). A brief overview of human energy metabolism and its relationship to essential obesity. American Journal of Clinical Nutrition, 55: S242-S245.
Siconolfi SF, Lasater TM, Snow RCK, Carleton RA (1985). Self-reported physical activity compared with maximal oxygen uptake. American Journal of Epidemiology; 122:
Schneider PL, Crouter SE, Bassett DR (2004). Pedometer measures of free-living physical activity: comparison of 13 models. Medicine & Science in Sports & Exercise; 36 :
Welk GJ (2002). Physical activity assessments for health-related research. Champaign, IL: Human Kinetics.

35. Review Questions (Developed by the Supercourse team)
Is physical activity the same as physical fitness?
How much exercise is needed to reap the benefits of PA?
For what chronic diseases does PA appear to reduce risk?
We would appreciate your help with evaluating the content of this course. Please send completed Evaluation Form to with the subject "chronic disease supercourse evaluation"   
If you have any comments or questions, please send a message to