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EXERCISE, CARDIOFITNESS and CARDIOVASCULAR DISEASE

Abstract:  Risks of cardiovascular (CV) disease are related at highest significance to the Cardiovascular Fitness of individuals as measured by the CFR.  This fact is confirmed independently both by the review of all research published before about 1980, and by major research published since then.  There is only a rough and much poorer association of disease risks with overall activity calories estimated from questionnaires, probably because the Calorie measure does not identify adequately the key casual factor of exercise intensity.  Risk of CV disease is reduced 5.4% for each improvement of 1 in CFR or 1% in cardiofitness.  

Background:  The first and now classic study relating exercise and physical activity to heart disease was published by Morris in 1953.  We now have a half century of research on this most important subject.  A first and only previously published Global Analysis of this research was described in the Pulse Point Plan (Random House, NY,1982, Forrest H. Blanding, reviewed by top authority Samuel M. Fox, MD).  Thus rather than attempt to review the entire half century of research it seems more useful to first review what was learned during the first half of this period, and then bring the record up to date with the new research published since. (See also the separate analyses of CFR as a measure exercise and Cardiofitness;  Exercise and Cancer;  Exercise and death from all causes;  and Exercise, a summary of its benefits.  More formal research papers  Cardiofitness and Disease and the CFR also are included. 

A long prevailing theory of why exercise protects against heart disease has been that exercise of the body requires more energy to be delivered by the heart.  Thus as the body is exercised more the heart and its accompanying cardiovascular system in turn become exercised more.  Any muscle that is exercised more tends to become more fit.  Thus exercise - and the right kind of exercise - causes the heart to become more fit.  And a more fit and robust heart is one that is more resistant to a heart attack or failure.  Exercise of the heart also effectively exercises the entire CV system.  Exercise of the crucially important coronary arteries helps keep them more open and resistant to clogging.

As the heart becomes more cardiofit it produces more energy per beat and becomes more efficient. Thus to supply a given amount of required energy it needs to beat fewer times per minute.  Cardiofitness - or the efficiency of the heart and cardiovascular system - can be measured in two different ways.  A first is to actually measure the amount of oxygen a person can consume when exercising to absolute maximum possible.  This is measured by a value of VO2 Max, or the ml of oxygen a person can consume per kg of body weight per minute.  But the VO2 Max test is difficult, demanding, expensive, and entails some if minor risk. An approximation of cardiofitness can be obtained easily by measuring heart rate at a given measured load on a treadmill or exercise bicycle. (cardiofitness is used in Life Ahead to identify approximately what in research reports is called cardiorespitory fitness or cardiovascular fitness)

A vast amount of research has shown how different kinds and amounts of exercise produce cardiofitness.  Intensive continuous aerobic exercise that requires high heart rates will produce higher cardiofitness than does exercise at low heart rates. Thus exercise experts  and the American Heart Association have recommended exercising at maximum heart rates possible that are still considered safe.  But maximum heart rates are not required to produce good cardiofitness.  Generally, exercise at a level of about 7.5 calories per minute - that of a very vigorous walk or slow jog - will produce cardiofitness quite efficiently.   And exercise at much lower levels still can improve cardiofitness usefully.  The Pulse Point method described elsewhere herein identifies how various amounts of heart exercise usually will produce cardiofitness.

An alternate theory is that benefits of exercise are related simply to activity calories of exercise. Unlike cardiofitness, Calories of exercise are not usually measured, but must be estimated from questionnaires provided by participants. Gross calories of physical activity usually reported do not identify exercise intensity.  The same calories of exercise are produced from 1 hour of exercise at say 3 calories per minute intensity as from 20 minutes of exercise at 9 calories per minute intensity.  But the low level exercise will produce little if any improvement in cardiofitness whereas the higher intensity exercise done each day will produce very useful gains in cardiofitness.  A sedentary man generates about 900 activity calories per day of physical activity and still usually will be sedentary or low in cardiofitness.  But just 100 more activity calories per day of reasonably intensive exercise can produce a very substantial improvement in his cardiofitness.  Thus most Physical activity calories of our population produces little useful cardiofitness.

Thus it is of importance to know if the benefits of physical activity in reducing risk of heart disease are related just to activity calories, or to levels of cardiofitness, the more explicit measure of the efficiency and robustness of the heart.  A correct answer to this is a key need for identifying the kinds and amounts of exercise we need to do.  Further, if cardiofitness is the key, we have a potential measurement of our body that can identify risk that is not available from analyses of activity calories. Thus a key question is “Does the risk of heart disease relate better to cardiofitness than it does to just overall amounts of activity calories?”   Each individual research study provides only a statistical association of risk of disease vs. some measured parameter.  Thus it is not feasible to obtain an answer to this question from any past or new individual research study.  The answer must be the basis that best quantitatively explains the results of ALL available research in the Global data set.

The First Global Analysis:  44 different pre-1980 comparisons of the risk of individuals having differing amounts of exercise or physical activity were available for this first analysis provided in the above reference.  22 were for groups of occupations that involved different amounts of physical activity, 11 were for groups if differing amounts of leisure exercise, and another 11 were for groups have differences in both occupation and leisure.  The key objective of this analysis was to determine what amount of benefit could be obtained from differing kinds and amounts of leisure exercise, and how could a person obtain most acceptable and best protection from disease via exercise.  This objective continues to the same today.  Because occupational physical activity of our population has become increasingly less and is largely non-actionable, actionable health actions must focus on leisure exercise.

As of 1980 no published research had actually measured the effect of cardiofitness levels on risk of disease. But a large body of research on how different occupations and types of exercise produced cardiofitness was available.  Thus it was possible then to develop a global analysis of this question by estimating from this second source of research the approximate cardiofitness levels probably obtained by the various groups studied for heart disease.  Although this posed the problem of using estimated rather than determined values, values of activity calories also had to be estimated similarly from such secondary research via questionnaires and these involved substantial inaccuracies.  The measure of cardiofitness used now called the CFR is an index of the popular physiological measure called “VO2-Max”. CFR approximates the ratio of VO2 Max to the average VO2-Max at age for sedentary men and women expressed as a percent.  Thus a value of CFR of 100 for a man or woman of any age identifies an average or sedentary level of cardiofitness.  Values above 100 identify increasingly better cardiofitness, values below 100 indicate poorer than average cardiofitness.  For reference, actual levels of VO2-Max are 0.33 times the CFR for men and 0.25 times the CFR for women at age 50, the approximate age of most research. See much more on the CFR.

Risk Relates Best to Higher Intensity Exercise and Cardiofitness:  The tabulated results of all then published research in the above book show near obviously that the risk of heart disease was related much more accurately to the higher intensity levels of exercise that produced cardiofitness than to overall amounts of activity calories.  Railroad section men and longshoremen that consumed up to 7,000 activity calories per week obtained no more benefit to heart disease than did a number of groups that exercised 700-1500 per week in their leisure.  The average values from all studies published showed that leisure time exercise produced the same reduction in heart disease as did a three times higher number of calories of occupational type exercise. Occupational activity usually takes place at lower intensities of physical activity than occurs in leisure exercise.

More rigorous tests via statistical methods confirmed objectively that risks of cardiovascular diseases related much more closely to cardiofitness than to activity calories. Correlation coefficients of risks of all Coronary Disease, Coronary Death, and Death from All Causes vs the CFR or VO2 Max from the 44 available pre-1980 sets of actual research data were very high values of 0.931, 0.951, and 0.976 respectively.  Risks also were associated with activity calories, but at lower levels from 0.738 to a best of 0.871.  More importantly, the standard deviations of risks of heart disease from formula averaged nearly twice higher using activity calories than using cardiofitness.  The specific formulas for these relationships from all pre-1980 research are appended following Table 2

Risk of heart disease from this first quarter of a century of research was found to decrease about 6.8% for each additional CFR of cardiofitness.  This identified a risk factor of about 0.50 for a 10 increase in CFR, and of about 0.25 or only 1/4th of average for 20 added CFR.  The highest likely difference in cardiofitness then found among the populations then researched for heart disease was probably about 20 CFR.  The impressive correlations developed and published in 1982 follow for each category of heart disease and for death from all causes.  Keep in mind that each point in these graphs represents results from a study usually of several thousand different individuals.  All relationships must originate at zero effect for zero difference in CFR.  Thus the charts present results of all useful research published to this date. The index then called the HPI was more recently changed to the more descriptive cardiofitness Ratio, or CFR

(Please click on 'x' to bring up chart)

 Relationship of the HPI and CFR to Risks of Coronary Heart Disease and Death

Starting about 1970 researchers realized the physiological significance of a more efficient and robust heart that develops from good cardiofitness as the probable protector from heart disease.  Research showed that cardiofitness was obtained most effectively from exercise at very high heart rates approaching 85% or even 90% of maximum possible heart rate. Thus recommendations were forthcoming that people should exercise this way to become ‘Cardiofit’.  These recommendations of the American Heart Association supported by a sea of books on how to exercise this way undoubtedly were constructive and probably helped prolong millions of lives.  But unfortunately they were misleading because they focused attention away from much of the exercise that can contribute to both cardiofitness and health.  Many and perhaps most people do not find high heart rate exercise acceptable.  High heart rate exercise IS the most efficient exercise that produces cardiofitness.  But both the first Life Ahead 1980 analysis and all later studies of cardiofitness show that most people can obtain important benefit from much lower intensity exercise than identified via high percent of maximum heart rate targets. 

Essentially every one of the millions of people included in the research both before 1980 and most of those included in studies published since did most of their exercise at far more moderate levels than "90% of maximum heart rate".  The reduction in risk of disease associated with probable levels of cardiofitness in the above first 44 studies shown in the above plots was obtained mostly by people who performed very usual and practical levels of exercise.

The all too common conception that “cardiofitness means high target heart rate aerobic exercise” is incorrect.   Although many researchers  now realize this, some have moved much too far in the reverse by ignoring the reality and importance of cardiofitness, by ignoring the key importance of monitored heart rate exercise, and by deprecating higher heart rate exercise and claiming that "Only moderate exercise is useful in protecting health."   Even today our population has not been provided with a widely accepted and easily understandable measure of cardiofitness such as the CFR.  Millions today exercise without learning what their cardiofitness either is or means, and what they accomplish from their exercise.

As will be shown later, major contributions of the CFR cardiofitness measure are (1) its identification of the extraordinary risk that accompanies very LOW levels of cardiofitness, (2) its far sharper identification of the exercise the produces benefit and (3)  As cited previously, it provides a valuation of an individual’s cardiovascular risk not previously available that may be the most important of all known major risk factors.  Although brisk steady walking and moderate exercise can be quite beneficial, higher levels of cardiofitness from more vigorous exercise can provide can develop better and even outstanding levels of health protection.  And it is unlikely that any amount of leisurely or intermittent walking will produce much benefit in reducing risk of major disease.  

The More Recent Research:   Research published since 1980 provides some highly significant new contributions to that from earlier research.  Most important were 28 comparisons from 11 published studies described following that show the risks of heart and cardiovascular disease related to MEASURED values of cardiofitness.  Also important were the specific studies of the risks reductions obtained from walking, the cardiofitness exercise that most people are willing to do.  And certain other studies provided perspective and confirmation of the probably casual role of cardiofitness..

Table 1 summarizes the studies that separated groups researched by differences in cardiofitness using an actual fitness test.  Studies 2, 4-7 and 9 measured cardiofitness directly on the groups.  These tests that included use of the Balke treadmill test and various bicycle ergonometric tests provided data on the researched populations that could be translated to probable values of the important cardiofitness measure of VO2 Max. Although these translations were not provided in the reports of most of the studies, they were developed for use in the results that follow and for use in Life Ahead. The values in Table 1 provide the cardiofitness levels in CFR derived from these translated VO2 Max values.  Cardiofitness values for the other studies were derived from the usual population distribution values of cardiofitness as described separately.

A problem in most of this research was that cardiofitness was measured only at study start, but disease was recorded for periods ranging from three to seventeen years thereafter.  Cardiofitness is well verified to depend mostly on exercise performed during a past 3 to 6 months.  Exercise habits of groups of people do not maintain the same over very long periods of years. Thus the actual differences in cardiofitness of groups researched must have been much different at the time heart disease was recorded than those measured at study start, 

But fortunately, an approximate answer to this problem can be developed.  A review of results of several studies showed that differences in exercise and cardiofitness of groups usually decline at a rate of about 16% per year. People of poorest fitness tend to exercise more, and those of highest fitness often start exercising less.  This rate of change in cardiofitness of groups with time was quite similar in studies of Leon, Morris, the Cooper Institute, Erikssen and Schnohr.  Paffenbarger found similarly that only about 10% of those classed as “High activity” were still in this group 13 years later. This also confirms an average decline of 16% per year in the differences in exercise obtained by groups.  Thus we have the reality that the true differences in both amounts of exercise and cardiofitness between groups must have been much less when heart disease struck than when measured many years earlier at start of the studies.

Another confirmation of this comes from results for study #9 of Hein.  He found a risk ratio for heart disease of 0.47 for the entire 17 year term of the study for a most active group. Risks at earlier years derived from the provided survival curves indicate risk ratios increasing from a far lower 0.17 as of year 3 to 0.30 as of study year 7.  This again implied clearly that actual average differences in cardiofitness of groups in the long term studies probably were only a fraction of those at study start.  Or that the true risk benefit for cardiofitness of the most active group really was much closer to a very low 0.17 (or about 6 times) than to the overall study value of 0.47 (about two times).  Values in Table 1 thus include both measured values of cardiofitness at study start and probable values of an average CFR level over the life of the studies assuming an average regression in exercise differences of 16% per year.

The results in Table 1 are of major potential importance to the future health of our population because they identify a health risk factor that has been largely overlooked.  Note that nine different confirming risk ratios from the different studies in the range of 0.12 to 0.25 accompany highest measured levels of cardiofitness.  These multiple results reveal risks for good cardiofitness 4 to 8 times lower than those for low cardiofitness.  These are far greater benefits than found in any study of differences in activity calories.  In fact they are larger than obtained from usual differences in nearly every other coronary risk factor.  Table 1 includes some risk levels for overall cardiovascular disease that are similar to those for heart disease. Risks of disease also correlated at high significance with differences in CFR at study start, but are more accurately correlated with estimated average CFR differences during the term of the studies.

Another objective answer to the question "Which measure fits actual results of all of the available research best:  Physical activity calories or cardiofitness?" now becomes possible. (Recall that a first answer was derived independently from the pre-1980 research.)   The correlation coefficient of the relationship of cardiovascular risk to measured difference in average cardiofitness in CFR for study comparisons in Table 1 is a very high 0. 939, about the same as 0.931 and 0.951 values found from above earlier research wherein CFR values had to be estimated.  As for the pre-1980 research, the correlation of of risk vs. cardiofitness was far better than that for risk and activity calories.  The actual coefficient of the CFR from measured cardiofitness values was 0.0555 (5-95% limits 0.048-0.063) vs that of about 0.068 derived from earlier studies using estimates of  cardiofitness.  This suggests that the earlier estimates of differences in population cardiofitness were about 25% too low.  But more importantly, the effects of cardiofitness on disease are verified similarly at extremely high significance from the research done in both the pre-1980 and post 1980 eras.  The ‘t’ values of the coefficients were of 13.7 from the pre 1980 and 15.5 from the post 1980 research.  These values are many times the ‘t’ value of 2 needed for the usual 95% level of significance, and at a significance level in the billions to one. Thus we now have a half century of research results confirming a very large effect of cardiofitness on heart disease at highest significance. 

This updated and quite accurate valuation from more than 20 research comparisons of actually measured cardiofitness shows that each increase of 1 in CFR reduces risk of heart disease by 5.4%.  (memo:  later analysis of all data derive a 6.4% risk per CFR)  Most studies of heart disease included groups of so-called "Active" and "Inactive" people that had probable differences in their true cardiofitness of about 10 CFR.   The risk ratio of heart disease for this difference in cardiofitness is an expected 0.57.  Attempts to separate "fit" and "unfit" people using estimated numbers of Physical activity calories from questionnaires probably identified groups differing in cardiofitness only by about 10 CFR..

An increase of 30 CFR obtainable only from a higher level cardio type exercise program should produce a risk of 0.19 or a risk of about 1/5th of that for those not exercising.  Life Ahead now accepts only the risk from a maximum CFR difference of 30 CFR as well verified by actual research results.  But it seems likely that larger improvements in  cardiofitness could produce still lower coronary disease risks to one tenth or lower than those for “Inactive” people.  Improvements in the cardiofitness of some groups of individuals higher than 50 CFR were actually measured at the start of some research studies.  

Correlations of risk ratio benefits with activity calories are significant both at base line or adjusted for average during study term, but with a much higher average standard deviation from correlation than when using the CFR or cardiofitness basis. This probably is due to the fact that a largest portion of usually measured activity calories does not contribute usefully to cardiofitness.

A Half Century of Research on the Risk of CV Disease Death and Exercise and Cardiofitness:  The plot in Figure 2  displays the Global results of the pre-1980 research shown in Figure 1 via the open circles relating differences in risk of CVD death and differences in cardiofitness.  Included as solid circles are the results of most post-1980 research on the same factors.  Note that the post 1980 research that included many results based on actually measured differences in cardiofitness developed a near similar confirming trend of risk vs. cardiofitness to that of the pre-1980 research.  The post 1980 research extended the relationship to much higher values of cardiofitness. Keep in mind that each point in this Global relationship represents results of an entire study comparison, usually derived from a thousand or more and in some cases on more than 40,000 individuals.  The HPI used in the 1980 analysis and CFR used now have closely similar values.  Figure 2 effectively presents results on millions of individuals.  

                                                           Figure 2

Walking, Cardiofitness and Risk of Heart and Cardiovascular Disease:   Table 2 provides results of research on walking that was found useful for the Global Analysis.  Two facts become immediately evident.  First, walking did reduce risk of cardiovascular disease.  But second, except for one risk ratio at high error margin, the maximum reductions in risk measured from walking are to a risk factor of about 0.50.  Thus although walking does produce a quite useful reduction in risk, it does not accomplish the 4-8 fold reductions in risk from higher levels of cardiofitness verified independently by nine of the data sets in Table 1.     

Very little useful information was found in Medline indexed research on the cardiofitness improvements from walking programs.  Thus the estimates of cardiofitness listed in Table 2 were obtained from the Life Ahead exercise module that derives cardiofitness from the separately described Pulse Point method.  Using these estimates, the effect of CFR produced from walking is 0.0514 (5-95% limits 0.037-0.066).  This identifies a 5% reduction in cardiovascular disease for each improvement of 1 in CFR from walking that is statistically consistent with the 5.4% per CFR effect of cardiofitness obtained from all types of exercise as shown in Table 1.

Thus the simple measure of cardiofitness called the CFR explains the risks found in nearly every pertinent research result on exercise and heart and cardiovascular disease within their 5%-95% margins of error published during the past half century.  The measure explains not only the quite large reductions in risk accompanying high levels of  cardiofitness but the lower but still useful reductions in risk obtained from walking programs.  As shown separately, cardiofitness also is related at high significance to cancer to and to overall risk of death.  

This verification opens up a bridge between the large body of research about how cardiofitness develops from different kinds of exercise and the research on how cardiofitness determines risk of major diseases. The CFR discussed separately in detail links the population research on disease with the physiological research on cardiofitness.  By integrating the two families of research on physiology and on risk of disease it becomes possible to forecast the probable benefit of almost any conceivable type of exercise on risk of major disease by identifying its effect on cardiofitness.

Other Studies of Exercise and Cardiovascular Disease:  Much of the research published since 1980 included more and more studies of exercise based on differences vs. activity calories vs risk without any accompanying information on exercise intensity or cardiofitness.  Such studies nearly all showed the same result:  “More exercise calories reduces risk of heart disease nearly in half.”  Because high level exercise calories can produce a many times higher benefit than do low intensity calories, a measure just of the effect of total activity calories on risk does not contribute to the design of effective exercise programs.  But some of these more recent studies did contribute usefully.

First, we do have some very useful research on the health benefits of walking.  This is included herein separately.  This shows with high accuracy the risk benefits to heart disease for walking various hours per week at different levels of pace in miles perhour..  It reveals sharply that the pace of walking can be far more important than the hours walked.  And once again that calories of walking  do not explain its benefits. .

Morris (Br Heart J, 1990, 63:325) who published the classic original research on physical activity and heart disease showed from a large study in England that benefits of exercise in reducing risk of heart disease were highly consistent with the way that exercise is known to produce cardiofitness.  Very extensive walking at modest intensity levels produced little or no benefit.  Fast walking produced very substantial benefit.  He concluded that only regular and at least fairly intensive exercise done year around and NOT seasonal produced benefit.  Exercise that was not moderately vigorous produced no benefit.  Magnus (Am J Epidemiol 110:724) also found no benefit for exercise such as gardening that was interrupted seasonally, and Mensink (Epidemiol 7:391) found the low risk factor of 0.26 for CVD mortality only for “intense activity”. 

There has been publicity claiming the "Gardening will lower your risk of heart disease."  Thus conjecture probably develops from rather high values listed in some tables of activity calories that really were derived for  "Digging in the Garden.".  Benefits from usual gardening such as weeding, watering, fertilizing etc. that are done only seasonally probably are miniscule.  

An interesting study of Arraiz,  (#8 in Table 1 following) on a Canadian population of about 33,000 provided a direct demonstration of the much larger effect on the same population of actually measured cardiofitness vs attempts to classify exercise by estimates of physical activity from questionnaires.  About 2300 individuals took a simple fitness step test. Those that did not pass the test had a 4.6 to 7.8 times higher adjusted rate of CV death than those that passed the test. The risk of the more fit group was about 0.19 of that of the less fit group.  Yet those that had lowest estimated physical activity calories had a maximum advantage of only 1.5 times, for a risk factor advantage of only about 0.67.  This was a direct confirmation of the failure of estimates of physical activity calories of exercise to identify most probable differences in probable cardiofitness and CVD risk on a similar population.

Tanasescu (JAMA 2002,288:1994) highlighted from the Health Professionals Study the major importance of exercise intensity on risk of heart disease.  Large differences in amounts of walking reduced coronary heart disease by 26% (only 10% adjusted) whereas differences in walking intensity pace presumably at some similar time of walking reduced risk by 55% (49% adjusted).  This clearly reveals that miles of walking can be of little value per se in assessing risk unless walking is done at an adequate pace, and that pace, and not miles, hours or overall activity calories is the key to benefit.  A somewhat similar result was found for all measured differences in activity calories. Unfortunately, most information in this study was presented via statistical parameters that could not be translated usefully to use in Life Ahead or to peoples’ actual exercise. 

Manson, (N Engl J Med 2002, 347:716) showed further via the Nurses study, also # W4 in Table 2 following, that for a given energy expenditure in activity calories or Mets that the more vigorous exercise produced substantially more benefit. activity calories without a quite substantial accompanying parameter for exercise intensity again is shown to be inadequate.  This again points to cardiofitness and not gross activity calories as the primary factor of benefit.

LaCroix and Hakim, (Studies W2 and W3 in Table 2) showed the striking effect of exercise and walking on the reduction in risk of those in the above 65 year old group, and many in this group continued to their 80’s. There is no diminution in the risk benefit of cardiofitness with age as occurs for the reduced risks with age for cholesterol and smoking.  Hakim also showed impressively the benefit effect of exercise in reducing the overall death rates of these much older than usual people.

There may be a limit to benefit from moderate level exercise:  There was a tendency for actual results for many miles of walking to be lower than that expected from the formulas.  Morris found minimal benefit for 7 hours or about 18 miles per week of “usual” walking.  London Postal Workers (Lancet 265:1052) obtained a risk reduction of only 29% for what probably was at least several hours and several hours of walking each day.  US postal workers obtained a higher 64% benefit for this large amount of walking, but this is still short of what would be expected.  Thus there may be a limit to the cardiofitness and reduction in risk of disease that can be produced from any amount of walking if it is not adequately brisk.

Little Useful Information shows benefits of specific exercises:  Except for the research on walking, the only useful study found for other types of exercise is that of Schnohr (Ugeskr Laeger 2001, 163:2633) showing a risk reduction to 0.37 ((0.19-0.71) for jogging. Attempts to identify benefits of different exercises via statistical regression such as in Tanasescu above did not produce credible results for exercises other than walking.  Statistical regression cannot separate out the effects of inter-correlated variables, and exercise habits are multiple and much too deeply inter-correlated to be identified correctly using this method.  (See more on regression).  Direct comparisons of those doing specified amounts of and intensity of jogging done both currently and for at least a last 6-12 months with those doing no exercise whatsoever are needed for useful results. Because running and jogging have been and are the most prevalent higher intensity exercises, and because these are the only widespread types of exercise that can produce the 30 to 50 improvements CFR obtained in the research of Table 1, it seems likely that jogging and running produced much of the larger reductions in risk found from research on cardiofitness to date. 

There is no assurance that any exercise will provide complete protection from heart or other major disease.  Quite a few serious runners have died of heart attacks during their exercise. A noted example was Jim Fixx who wrote the recommendation on the cover of my 1982 book,  Jim was author of the best selling Book of Running.  Fixx and some others were found to have had near or completely clogged coronary arteries, and also had serious family history and/or other high risks of disease. An analysis of the risks of runners in Rhode Island (P. Thompson, JAMA May 14, 1982) showed that when analyzed per minute of actual activity, joggers were at higher risk during those running minutes than were average men at home or elsewhere.  This hardly is surprising, as high level exercise would be expected to trigger an impending attack that probably would have happened later.   But when analyzed in terms of more meaningful death rates, the joggers had only one twentieth of the death rates experienced by average men of the same ages in that state.  Nevertheless everyone - including those that exercise the most - should be making regular visits to their doctor.  Jim Fixx had not done this.

Exercise, Cardiofitness and Risk of Stroke:  Table 2 provides the more important studies found published relating risk of stroke the exercise. Essentially every study confirms that physical activity and exercise can substantially reduce the risk of stroke, and that moderate exercise can reduce risk of stroke in half.  Most studies suggested that the key benefit of exercise was for ischemic stroke, but some studies showed benefit for all types of stroke.  The values in Table 2 refer to risks of all stroke or death from stroke.

No available study found here related stroke to measured values of cardiofitness.  Table 2 includes the approximate estimates of activity calories included in the different studies and the now estimated CFR differences on the populations studied.   The best correlation again was for the risk of stroke vs. estimated average CFR during the studies.  This showed a coefficient of 0.0578 (5-95% limits 0.046-0.070) that is near identical to the 0.0555 value for coronary and all cardiovascular diseases.  Life Ahead now uses the 0.0555 value to compute benefit of cardiofitness on risk of all forms of cardiovascular diseases.  The results on stroke are provided together with other formulas relating risk of disease to cardiofitness detailed following Table 2.

Cardiofitness and Well-Days of Healthy Life:  A typical study of exercise (or any other factor) will find that a largest number of disease events are prevented by a first improvement in risk.  For example, if a hundred heart disease events are noted for an inactive group, an increase of 12 CFR will reduce risk in half, as rr = 0.50;  and an increase of 24 CFR will reduce risk to 0.25, rr = 0.25; and an increase of 36 CFR will reduce risk to 0.125.  But disease events will be reduced in half or by 50 for the first 12 CFR, to 0.75 for 25 more events for the 24 CFR improvement, and to 0.875 for only 12-13 more for the third improvement.  This leads to the impression that the BIG improvement is obtained for the first 12 CFR, or moderate exercise, and much lesser amounts are contributed by higher exercise.  This implies a conclusion that is incorrect for an individual.  

When these risks are translated longitudinally into likelihood of disease and life for an individual or group, we find that successive reductions in risk produce a similar extension in health and life.  Consider for example a man with initial risk of say 1.0 of age 30 with a usual risk of heart attack increasing at 8% per year that is destined to have a disease attack at age 40 when his risk becomes a value of 1.08^10 or about 2.16. If he reduces just before then his risk in half, to 4% per year he will obtain 20 more years before the risk reaches the same or trigger level of 2.16. Or for a reduction in risk to 1/4th or to 2% per year he will get 40 more years to the attack.

Life Ahead computes all diseases by their lifecycle rates of progress based on NIH statistics by disease and their modified risks by factor and their interactions for each year of life.  The program confirms as above that each increase in cardiofitness in percent or each increase in CFR will produce a near similar increase in Well-Days of life.  A 10 CFR improvement from say walking will for a man of age 50 increase Well-Days by about 3.5 years.  A increase in CFR of 20 from somewhat higher level exercise will increase Well-Days by more than 6 years.  And an increase in CFR of 30 from a really good cardio program (the maximum now accepted by the program) will increase Well-Days by about 9 years.  This assumes certain base values of age and risk and that cardiofitness is the only health change for an average US man or woman.  If other health improvements were made simultaneously, the further contributions of such improvements in cardiofitness from so-called collapsing risks would become lower.  Thus  it is not true that the first reduction in risk accomplishes the major reduction in Well-Days of life.

Mechanism for Reduced risk of Heart and Cardiovascular Disease from Cardiofitness:  It long has been hypothesized that the exercise that produces cardiofitness produces a more robust and efficient heart less vulnerable to attack.  This hypothesis may be substantially correct, but the mechanisms via which cardiofitness reduces risk of coronary heart and other diseases probably differ.  The possible mechanisms are discussed in the accompanying Summary of exercise and major disease.

The use of cardiofitness as a risk provides an major advantage over the use of estimated activity calories or other measures of exercise.  First and as above, it provides a far sharper identification of risk of cardiovascular diseases. As shown elsewhere herein cardiofitness identifies best both the risk of cancer and the overall risk of death.  Second, it is a state of the body that can be directly measured via a variety of methods including some simple exercise tests as will be shown here in Life Ahead.  And third, cardiofitness is in part genetically endowed.  Thus measured values of cardiofitness can identify a previously unidentified genetic risk in addition to valuing better the benefits of exercise.  More on this is included in the above Summary.

A low cardiofitness can identify a very high health risk that today is largely  unknown not only to our population but is not recognized by most of today's health professionals. Some individuals that do claim to exercise still can have dangerously low levels of cardiofitness.  With a recognition of this key risk together with more concise quantification of other known risks Life Ahead may be able to forecast many of those now unexpected heart attacks that kill at untimely early ages - and show how they can be avoided.