OUTLINE

• Modern Disease
• Research Methods
• Definition of Physical Activity
• Exercise and All-Cause Mortality
• The Exercise Dose
  • Fitness vs. Physical Activity
  • Accumulation vs. Continuous Activity
• Comment
• Policies on Physical Activity and Disease

In the past, you were either sick or healthy. Modern chronic diseases are different. Modern chronic disease is on a continuum from health or wellness to disease, where a person can be moving from varying stages of wellness to various stages of disease.

Modern chronic disease is characterized by a malfunction in a physiological process. For example, in diabetes, the insulin does not function properly.

The majority of modern chronic diseases are incurable. The Centers for Disease Control have identified over 2600 diseases in this world, in which only about 500 have a cure.

Although these diseases are incurable, they are controllable. Modern medicine controls disease by pharmacological management, surgical management, and/or by lifestyle management. Because physical inactivity plays a significant role in the etiology of disease, physical activity plays a similar role in the prevention and rehabilitation of these diseases.

The etiology of modern chronic disease cannot be attributed to one single factor. The interaction of genetics and lifestyle appears to contribute to most to the etiology of modern chronic disease. Lifestyle accounts 51% of disease, whereas genetics accounts for 49%. For most of these diseases, one must first have the genetic predisposition for the disease. Subsequently, the way one lives their own lifestyle determines whether the disease manifests early or later in the life span. What are these lifestyle factors? They include:

• Nutrition
• Diet
• Smoking
• Stress
• Physical Inactivity

Nutrition is the kind or quality of the food eaten whereas diet is the approach to consuming the food. For example, a nutritionally balanced intake includes foods from all of the food groups, in proper amounts. The diet, or approach to eating, can be either nutritionally balanced or not. Diets can be modified by not only the consumption of too few to too many calories, but by the distribution of the calories. For example, all the food can be eaten in one meal a day or spread it out into six meals a day. The healthy approach to eating is to eat an isocaloric, nutritionally balanced diet in three or more meals a day.

Smoking cessation can have the largest impact on the health improvement of the world. Twenty percent of the deaths in the US can be attributed to tobacco use. Smoking is associated with cancer, heart disease, gastric ulcers, chronic bronchitis, emphysema, and cerebrovascular disease. Smoking accounts for at least 30% of all cancer death. In addition to being responsible for 87% of lung cancers, smoking is also associated with cancers of the mouth, pharynx, larynx, esophagus, pancreas, uterine cervix, kidney, and bladder. Smoking is also a major cause of cardiovascular disease.

Physical inactivity, only recently, has been identified as a leading factor in the etiology of modern chronic disease. Hence, role of physical activity in the prevention of disease is the topic of this page.

Research methods, definitions of physical activity, and the measurement of physical activity must be included a discussion to understand the role of physical activity in disease prevention. The research methods are simple. However, the definition of physical activity and the methods to measure physical activity are not.

RESEARCH METHODS

Research methods include case studies, epidemiology, and clinical trials. Case studies are usually how research in a medical arena begins. For heart disease, the first case study to support exercise rehabilitation was presented in the 1960s, by Dr. Herman Hellerstein, who sent one of his patients to the YMCA to exercise after a myocardial infarction. The patient made a remarkable recovery. In sharing the course of treatment for this one cardiac patient through a case study presentation, the modern cardiac rehabilitation movement began. More case studies followed which justified bigger population based studies.

Epidemiology is the study of the interaction between a disease and the disease causing factors in large populations. In epidemiologic studies, the relationship between the host (patient), agent (cause of disease) and environment are investigated in two different ways. In Incidence Studies, the occurrence of a disease is associated with a prior event, whereas in Prevalence Studies, the number of cases of a disease is measured at a given time. Prevalence studies are more cross-sectional in nature whereas the incidence studies may take years to make the associations with "prior events" (i.e. life-style factors at a younger age). Incidence studies would be found more than prevalence studies in exercise research. In these studies, an attempt would be made to develop a link between physical activity or inactivity (at a prior time) and subsequent disease (current time). Epidemiology research usually has hundreds to thousands of subjects.

Risk is usually established in epidemiological studies; although it can be determined from clinical trials too. Risk can be expressed as:

• Relative Risk (RR)
• Risk Ratio
• Odds Ratio

Relative risk is the ratio (also called Risk Ratio) of the probability of a disease developing relative to the exposure. That is, the ratio of the disease for non-active vs. active individuals.

RR= Probability of non-active individuals
        Probability of active individuals

RR = a/(a+b)
         c/(c+d)

Odds Ratio is ratio of the outcome in the two groups; the odds of disease in one group vs the odds in the second group. Odds ratio is can also be considered a measure of effect size.

OR = ad
         bc

Epidemiologic studies can help to identify an association between physical inactivity and disease, but it does not necessarily mean that physical inactivity causes the disease. This dilemma with epidemiologic studies is called "Selection vs. Protection". The question becomes, does the exercise truly prevent the disease (i.e. protection) or are the healthy people just healthy enough to do the exercise (i.e. selection)? Clinical trials, then, are the next step in answering these questions.

Clinical trials or Intervention Studies are experimental designs, which attempt to isolate cause and effect. Clinical trials would be found in rehabilitation or disease treatment studies whereas interventions studies would found more in prevention studies. Exercise or physical activity "treatment" groups and control groups are an integral part of clinical trials and intervention studies. Randomization into treatment and control groups is essential in clinical trials. In the case of exercise studies, the control group would not exercise and the treatment group would. Then, after a period of time, the incidence of disease would be observed in both groups. If the disease occurred in the control group and not the treatment group, then prevention of the disease could be attributed to exercise.

DEFINITION OF PHYSICAL ACTIVITY

What is exercise? What is physical activity?

Physical activity is any bodily movement produced by skeletal muscle contraction that results in increased energy expenditure. Gardening, house cleaning, occupational activities, and recreational activities are all included within the realm of physical activity.

Exercise is planned, structured and repetitive bodily movement done to improve or maintain one or more component of fitness. The components of fitness are cardiorespiratory endurance, flexibility, muscle strength, and muscle endurance.

Yes, by these definitions, exercise can be considered to be physical activity. So, when we refer to physical activity, we need to agree that we are defining the low intensity activities that cannot contribute to improved physical fitness.

MEASURING PHYSICAL ACTIVITY

Defining physical activity and exercise is much simpler than trying to measure them. Exercise is not a simple variable.

It is not a dichotomous "yes" or "no" variable like smoking.

It is not a continuous variable like cholesterol or blood pressure, where the values range from low to high and any value in between.

Exercise is a multidimensional variable that can be described by mode, frequency, duration and intensity.

There appears to be as many ways to measure exercise, as there are ways to exercise.

• LaPorte, RE, et al. Assessment of physical activity in epidemiological research: problems and prospects. Public Health 100:131-146, 1985.
• ACSM: A collection of physical activity questionnaires fo health-related research. Medicine and Science of Sports and Exercise 29: Supplement 6, 1997.
• ACSM: Objective monitoring of Physical Activity. Medicine and Science in Sports and Exercise 37: Supplement 11, 2005.

Tables 1 & 2

EXERCISE AND ALL CAUSE MORTALITY

All-cause mortality is the documentation of any and all causes of death. The top ten causes of death in the US is illustrated to the right. Cardiovascular disease leads the list. Cancer is a close second. Pulmonary disease and diabetes also top the list. A common underlying disease for all of these diseases is obesity. Morbidity is the incidence of the disease whereas mortality is death from the disease.

Epidemiologic research in physical activity and heart disease began in the late 1940's. A significant inverse relationship was found between physical activity and risk of coronary heart disease and the associated risk factors. These findings were consistent and strong. Recently, the epidemiologic research has been expanded to observe more modern chronic disease.

• Powell, K.E., P.D. Thompson, C.J. Caspersen and J.S. Kendrick. Physical activity and the incidence of coronary heart disease. Ann Rev Public Health, 8:253-287, 1987.

If the relationship between risk and activity were graphed for these epidemiological studies, the relationships would be similar to those plotted to the left. That is, the largest change in risk is found between the sedentary to some activity.

One of the more classic series of studies was carried out by Blair and associates from the Cooper Institute in Dallas Texas, USA. The first study was reported in 1989. Blair and colleagues observed the relationship between physical fitness, measured by time on a treadmill test, and all-cause mortality in a group of 10,244 men and 3,120 women who visited the Cooper Clinic for fitness evaluations. They followed these people over an eight-year period and found the causes of death for 240 men and 43 women who died during the eight-year period.

• Blair, S.N. et al, Physical fitness and all-cause mortality: A prospective study of healthy men and women. JAMA 626:2395-2401, 1989

These relationships were plotted in three dimensional graphs, as illustrated on the right. The X axisof the graphs is the fitness categories from one to five. However, they were condensed into three fitness categories, 1, 2-3, and 4-5. The Y axis is the relative risk. The higher the risk, the more likely the disease manifests. The Z axis is the lifestyle variable, the yellow being the lowest, the pink being the borderline, and the blue being the highest.

The findings were consistent for each lifestyle variable. As expected, the risk of death increased for each lifestyle variable as it progressed from normal to borderline to high (looking back, parallel to the Z axis). However, the risk within each lifestyle variable decreased as physical fitness increased (looking across, parallel to the X axis). The lowest risk being in the highest fitness category for the "normal" lifestyle group and the highest risk being in the lowest fitness category for the "high" lifestyle group.

Thus, low fitness appears to be associated with increased mortality and morbidity. As it turns out, the low fitness category was just as strong as the other lifestyle factors that had previously been associated with all cause mortality.

That is, physical inactivity appeared to be just as strong as high cholesterol, high blood pressure, smoking, family history, blood glucose, and body mass index, in all cause mortality.

The most significant decrease in risk of disease was found between fitness quintiles one and two. This has been interpreted as very little change in physical fitness can make a significant reduction in risk of disease. Many of the public policies on physical activity for the general public have been based on these findings. So, if we can encourage the public to move from fitness quintile #1 to fitness quintile #2 we will make a significant change in the health of this country. This change represents a change in max METS from <6 to >7 METS.

In summary, the important findings were: Physical inactivity is directly related to disease The risk of physical inactivity is just as strong as High Cholesterol High Blood Pressure Smoking Diabetes Family History A small increase in physical activity should make a significant reduction in risk

These findings were consistent with other epidemiologic studies, despite how physical activity was measured. However, the "selection vs protection" argument still can be made with any of these data. Was it just a coincidence that the low risk people were healthy enough to exercise or did physical activity really protect them from disease? To solve the selection vs protection issue, the question becomes,

• What happens to the risk when you increase your fitness?
• Will an increase in fitness result in a reciprocal decrease risk?

In an attempt to answer this question, Blair and colleagues observed the data in a different manor. They found that 9777 men who had been measured twice during the course of five years. These men were divided into four categories:

• Blair, SN, et al. Changes in Physical Fitness and All-Cause Mortality. JAMA 273:1093-1098, 1995

• those who were unfit for both test periods (un-un)
• those who were unfit at the first, but fit at the second (un-fit)
• those who were fit at the first, but unfit at the second (fit-un)
• those who were fit at both test periods (fit-fit)

Needless to say, they found that those who remained unfit still exhibited high risk of disease (Un-Un) those who became fit decreased their risk to 56% of prior risk (Un-Fit) those who became unfit exhibited low risk of 52% of the high-risk group (Fit-Un) those who maintained their fitness, exhibited the lowest risk at 33% of the high-risk group (Fit-Fit)

Paffenbarger and colleagues performed the same type of evaluation with the classic Harvard Alumni and Longshoremen Studies. They classified subjects as Sedentary (Sed) and Active (Act) instead of fit and unfit. They reported similar findings to Blair and colleagues, except for the group that changed from being active to sedentary (Act-Sed). Unlike Blair's group (Fit-Un), this group increased their risk of disease above the group that had remained sedentary (Sed-Sed or Un-Un). Blair and Paffenbarger measured different physical activity variables. Blair measured fitness whereas Paffenbarger measured physical activity.

Thus, changing fitness categories from unfit to fit or moving from sedentary to active, apparently reduces the risk of all-cause mortality. The epidemiological research in physical activity does not appear to reflect the selection vs protection effect.

THE DOSE

The epidemiological research focused on a range of physical activity and exercise. Are both effective in health?

• How much physical activity is enough?
• Is exercise as effective as physical activity for health benefits?

From the epidemiologic work, it appears as though changing from sedentary to the lowest level of physical activity may be enough to prevent modern chronic disease; 150 to 200 calories per day or 1500 to 2000 calories per week.

This translates to an accumulation of 30 minutes of moderate physical activity on most, if not all days of the week.

• Blair, S. N., Y Cheng, and J.S. Holder. Is physical activity or physical fitness more important in defining health benefits? Medicine and Science in Sports and Exercise 33:S379-S399, 2001
• Lee, M.I. and P.J Skerrett. Physical activity and all-cause mortality: what is the dose-response relation? Medicine and Science in Sports and Exercise 33:S459-S471, 2001.
• ACSM: Physical activity and health: dose response. Medicine and Science in Sports and Exercise 33: Supplement 6, 2001.

FITNESS vs. PHYSICAL ACTIVITY

Blair summarized the health outcomes for 49 research articles on physical activity and health, 9 research articles on cardiorespiratory fitness and health, and 9 research articles on physical activity, fitness and health.

There is an inverse dose-response gradient across physical activity There is an inverse dose-response gradient across categories of cardiorespiratory fitness and health outcomes The dose-response gradient for health outcomes is steeper across categories of cardiorespiratory fitness

Probably, however, the upper limit of exercise and disease prevention has not been investigated.

An obvious difference between exercise and physical activity can be found between the physical activity prescription for health and the exercise prescription to improve fitness. The amount of physical activity to produce a health benefit may not produce a fitness benefit.

Rx for Fitness: Mode: Cardiovascular FQ: 3-5/week Dur: 20-60 min Int: >60% intensity

Rx for Health: Mode: Physical activity FQ: most, if not all days of the week Dur: 30 min Int: Moderate (40-60%

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Accumulation vs. Continuous

The recommendations in most of the public policies state the physical activity can be accumulative; it does not need to be a continuous workout. The majority of the research focuses on physical work capacity (VO_2max) as the outcome varialbe. Lipids, body mass, blood pressure, and bone mineral content have been the outcome measure in others.

Only 16 studies were found to compare fitness and health outcomes between continuous and accumulative exercise. These 16 studies are summarized to the left. All 16 focused on VO2max; 9 on body mass; 6 on body fat; 8 on blood pressure; and 7 on lipids. The red bar indicates how many of the studies found no difference between continuous and accumulative; the blue bar indicates how many studies found "better" values for continuous; and the green indicates how many studies found "better" values for accumlative exericse. These studies do illustrate that it doesn't matter if the exericse is continuous or accumlative. It is believed that accumulative exericse may be more "accepting" to the public. Thus, acculative is recommended.

An accumlative session must be at least 10 minutes.

• Murphy, M.H., S.N. Blair and E.M. Murtagh. Accumulated versus continuous exercise for health benefit: A review of empirical studies. Sports Medicine 39:29-43, 2009

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Another of the unknown questions is the kinetics of these health changes. That is, cardiovascular fitness can change in six weeks of training. Do health changes ocurr that fast? Or do they take over shorter or longer periods of time? Blood pressure can reduce in one session of physical activity. On the other hand, how long does it take to reverse atherosclerosis or to lose weight?

• Haskell, WL. Health consequences of physical activity: understanding and challenges regarding dose-response. Medicne and Science in Sports and Exercise 26:649-660, 1994.

One advantage of targeting fitness, which improves health at the same time, is that the individual can experience the fitness benefits faster, which may be more substantial and rewarding in the long run. The perception of any kind of benefit can enhance motivation to continue to exercise. Health benefits are not exhibited as rapidly or as strong as the fitness benefits and may not promote adherence as well.

Modern Disease

Research Methods

Definition of Physical Activity

Exercise and All-Cause Mortality

The Exercise Dose

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