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HEART EFFICIENCY - the CFR:  WHAT IT IS and WHAT IT CAN MEAN

Abstract: The CFR identifies the amount of energy the heart can produce per beat as a percent of that of a average sedentary person of the same age and sex.  This useful index of Cardiofitness shows poor fitness for values below 100, and increasingly better values at levels above 100 CFR.  The CFR varies somewhat with usual lifestyle and occupation, and is partly due to genetics. But good values usually require cardiovascular or aerobic type exercise done continuously at moderately-high or high levels of intensity. Most of the overall physical activity calories of life that can contribute to body weight do not contribute very much to Cardiofitness.  As is shown elsewhere, CFR is the key index of exercise that is most sharply related to risk of coronary disease, cancer, and overall risk of premature death.  And a number of methods are provided in Life Ahead for people measure their own level of the CFR.  A more formal research paper on the CFR is included.

Fitness is a Black Hole:  The word fitness is a great buzzword.  It is a presumed goal of everyone that goes to a health facility to exercise.  It refers to exercise via weight training and exercise by running and even yoga.  It has been a subject of hundreds of research studies.  Yet few people including scientists have the slightest idea of what their cardiofitness levels is or means.  Few have even any idea about the fitness they gain from exercise.   The problem - incredibly - is this:   At this writing no consistent measure of fitness has been accepted that is useful to the public.   Fitness is like cholesterol without a blood test.  Or blood pressure with no cuff and listening device. Nearly every involved research study has measured fitness differently and expressed its results differently.

The word fitness can refer to variety of states of the human body. The word cardiovascular fitness refers to a robustness of the cardiovascular system, and word cardiorespiratory fitness presumably refers to a combination capability of the respiratory system and the cardiovascular system needed to bring about an overall physical capability.  Life ahead uses the simpler word Cardiofitness to refer to either of these measures, or what is more specifically, the efficiency of the cardiovascular system.  This is the key measure that can be improved by exercise.  And it is the measure demonstrated via this site that is best related to risks of major disease and death.

The idea of the CFR is not new.  A near identical concept was introduced in 25,000 copies of the Pulse Point Plan published in 1982 by Random House. That fitness measure of the HPI was reviewed and even named by the then top world authority on exercise and heart disease Dr. Samuel Fox of Georgetown University.  Yet no measure that could help the public understand their Cardiofitness and what this means to life has yet been adopted either by physiologists or by our Health Establishment. The fitness measure originally called the HPI was later changed to the HEF and now to the more descriptive name of Cardiofitness Ratio or CFR  

The CFR opens a completely new and fascinating picture about our Cardiofitness, how it develops, and what it means.  It provides a world of opportunity for new areas of research that can help people improve their health and extend their lives. And it provides a new independent measurable risk factor that may be more important than any other major population risk of death now known.

This Life Ahead site identifies what the CFR is and how it varies for different kinds of exercise and physical activity.  It provides a variety of methods for measuring the CFR in exercise facilities or by individuals themselves.  And it shows how improvements in the CFR can produce large reductions in risks of heart disease, stroke, cancer, and in the risk of death from all causes.

What the CFR Is:  The heart is the engine produces the energy needed to fuel our body.  Once it is exercised modestly it acts as a pump that moves the same amount of blood and oxygen each time it beats.  It produces its energy from a product of the energy from each beat times its number of beats per minute.  The total energy output of the heart at maximum heart rate from the maximum output a person can produce on a treadmill or bicycle is called VO2 Max, or the milliliters of oxygen the body consumes per minute per kg of body weight.

The maximum rate at which the heart will beat depends mostly on age, and which individuals can do little about. This decline in maximum heart rate with age reflects diminishing athletic capability as adults age.   But we can improve the efficiency of our heart, or the energy from each beat it produces, by cardiovascular type exercise.  The Cardiofitness Factor or CFR measures this all important capability of our heart. 

As we exercise more and over time become more cardiofit, our heart rate at rest or at a given exercise level becomes slower because a more efficient heart does not need to beat as often to supply its energy.  When exercising to a given heart rate our heart then produces more energy, and our VO2 Max increases.  But overall values of the VO2 Max per se do not provide a useful measure of the efficiency of our heart because they vary so much with both age and sex.  For example, a usual sedentary man has a VO2 Max at age 50 of about 33.  A usual sedentary woman that exercises similarly has a VO2 Max of only about 25.  A young person who is unfit may have a higher VO2 max than will an older person that is quite cardiofit simply because the young person's heart that is less efficient can beat at a faster rate.

The CFR solves this problem by a very simple method. The CFR identifies approximately the amount of energy the heart can produce per beat as a percent of that of a average sedentary person of the same age and sex.  This is the key factor that can be improved by exercise.  A given value an CFR has a near similar meaning for men and women of all ages.  An CFR value of 100 at age 50 means 100% of average sedentary that is mediocre level of Cardiofitness.  The CFR provides a simple and easy to understand measure. It is not an absolute  measure of our overall heart capability - this is what the VO2 Max number measures.  But the CFR is proportional to VO2 Max and thus retains the integrity of that basic measure. 

How the CFR Develops over Time:  The heart is a muscle, and Cardiofitness measures in part a capability of that muscle.  As for any other muscle, its effectiveness develops gradually over time in response to exercise.  An increase in exercise as for example the starting of quite brisk 2 hours per week of walking by a person with an CFR of 100 will not produce an immediate improvement in Cardiofitness.  Rather Cardiofitness will improve gradually at perhaps 2 % or 2 CFR per month, and reach a new level and plateau of perhaps 110 there after about 6 months. It then will increase no further unless exercise is increased further.  If exercise is stopped the CFR will revert back gradually to the previous 100 level.  A person's CFR is not constant, but can move up or down in response to any changes in regular lifestyle.  As a general rule, consider at least 6 months for a change in regular exercise to produce most of its potential change in Cardiofitness

How the CFR Varies with Exercise: The Cardiofitness level for average men and women of age 50 varies from a low value of about 70 CFR for those confined for weeks to bed rest to a high of about 180 CFR for an athlete in top condition. Those that do little more than sit and drive on most days  may develop Cardiofitness of only 85 or 90 CFR.  At this poor fitness you will puff going up just one flight of stairs too quickly, and a mile walk will seem like a tiring and unwelcome effort.

If you have a sedentary CFR of 100 you are fairly capable, but will probably will not move swiftly up a flight of stairs and will puff going up two flights. A regular fairly brisk walking program will move your up to 110 CFR and make you feel more capable on stairs. At 110 CFR a mile walk will be an easy effort.

Achieving a 120 CFR probably will require a very brisk or fast walking program, or some running and jogging or brisk lap swimming.  If you do regular serious aerobic type exercise, your CFR probably can increase to 130 or even to 140 or higher.  Your heart then will be 30% to 40% more efficient and capable than that of a similar person that has a more usual sedentary CFR of 100.  You can run up two flights of stairs easily and a fast mile walk will seem like a trivial effort.

How Cardiofitness in CFR Varies with Occupation:  Years ago researchers assumed most physical activity of individuals depended on their occupations. Average calories of physical activity for men then differed from 800 to more than 3000 calories per day for those engaged in different occupations.  Surprisingly, it was found from measurements of actual VO2 Max that despite these large differences in calories of physical activity, Cardiofitness was not produced effectively from occupational activity.  Allard (Canad Med Ass J 96:879) found an average of 99 CFR for those at "Light" physical activity and only 103 CFR for those at "Heavy" physical activity.  Gyntelberg (Danish Med Bull 20:105) found similar results of 98 CFR for light and 103 CFR for "Heavy" work.  A study in Norway found 125 CFR for lumberjacks, perhaps a most active of occupations. But office workers there at the same time in this very active society had an average CFR of 115. (Cumming, Canad Med Ass J 96:868). 

There are exceptions.  Farmers and sharecroppers that worked many hours per day in the fields probably developed good Cardiofitness.  Postman that walk many hours each day probably develop advantages of 10-15 CFR over average persons, and waiters in restaurants that walk much and fairly swiftly probably develop better than usual Cardiofitness.  Housewives with young children probably become more cardiofit than their computer watching husbands.  But today nearly all of the major physical activity of the past has been replaced by machinery.  Farmers ride tractors, earth is moved by bulldozers, and merchandise is moved by mechanical means.  Much more research is now needed on the Cardiofitness of people doing various types of work in today's occupation.

Life Ahead now recognizes a first and very rough estimate of the CFR based on a usual lifestyle.  With zero exercise entered the lowest suggested Cardiofitness from only sitting and driving is about 83.  This is assumed to move up stepwise for successively more active lifestyles to near 110 CFR for the most active usual lifestyle listed.  The contribution of exercise is added to these base values for usual lifestyle.

How Cardiofitness varies with Age:  Values of the CFR now used in Life Ahead for an average sedentary persons range from 111 at age 20 to 100 at age 50 to about 90 at age 70.  This reflects in part the fact that most people tend to be more physically active when young, and less active when older. But it also reflects in part that there probable also is a very small decline in basic efficiency of the heart with age.  It is surprising that this decline in basic cardio efficiency with age is so small.  Older people that exercise similarly have nearly the same heart rates at a given exercise load in treadmill tests as do those of younger people.

How Cardiofitness Varies Among Populations: The following table illustrates how the CFR of individuals in various populations probably varied.  The values were derived from plots of percents of the populations measured above various levels of CFR using the probability function for population percentages.  There can be some bias in the level of computed VO2 Max values developed and CFR values derived from the VO2 max because each Cardiofitness measurement was done via a different method.   But the participants in the Cooper Institute study of Blair were much more cardiofit than average probably because of the association of participants there with a very sophisticated exercise facility.

Percentages of those at CFR levels below about 85 CFR and above 140 CFR represent extrapolations rather than measured values.  But if these lower values are correct they suggest that some individuals suffer a genetic deficiency in Cardiofitness, as values of fitness below about 80 CFR are unlikely to obtained from usual lifestyles of low physical activity.  The Slattery population was railway workers that were more physically active than a usual population. More about these studies and references are cited elsewhere.   

               Percentages of Populations at Levels of Cardiofitness in CFR

Cardiofitness is Partly a Result of Genetics:  In addition to its development from exercise,  Cardiofitness is endowed in part by genetics.  The Cooper Institute developed questionnaires about the usual exercise of 13,000 men and 4,000 women that were measured for actual Cardiofitness.  A paper by Stofan (Am J Pub Hlth 88:1807) showed that 20% of men and women in the high fitness group claimed "No exercise".  And a very few that claimed good exercise remained in the low fitness group.   Dr. Samuel Fox who tested the Cardiofitness of many patients noted to me that an occasional robust appearing individual who did little claimed exercise could achieve a good treadmill measured result.  Nearly everybody should be able to achieve good fitness.  But some will need more exercise than others.

Life Ahead Provides a Genetic Factor for Cardiofitness:  Life Ahead now develops estimates of both activity calories and Cardiofitness in CFR from a detailed questionnaire about specific exercises and their intensity.  In absence of a measured value this estimate from exercise is used as a value for Cardiofitness.  If a measured value is entered, a ratio of measured to estimated value is developed.  If this ratio is above or below a minimal difference, a Cardiofitness genetic factor is developed and provided to program users.  A Cardiofitness genetic factor below 100 as for example 90 indicates that a user may have a poorer genetic Cardiofitness than average, and thus may need more exercise than usual to reach a desired Cardiofitness goals.  Keep in mind this:  It is the actual Cardiofitness that produces health benefits.  Some will have to exercise more and some less than average to reach a given goal.

Much more and better research is now needed on the genetic Cardiofitness of individuals.  Unfortunately present questionnaires on exercise are designed to determine only gross calories of exercise, and do not value adequately how exercise contributes to Cardiofitness.  The present questionnaire in Life Ahead attempts to value the effect of exercise that produces Cardiofitness and this can be a useful tool.  But better methods are potential.  More on how exercise contributes to Cardiofitness is included in the section on Pulse Points.

How Calories of Exercise Contribute Differently to Cardiofitness:  Heart disease researchers usually find that the health value of exercise is related to Physical Activity Calories.  This really is just a crude statistical association because groups of people that are more generally active also usually exert more of the selective type of Activity Calories that produce Cardiofitness. As shown elsewhere in the Global analyses of Life Ahead the health value of exercise is related much more accurately to Cardiofitness than it is to Activity Calories of exercise.  And as noted in the paragraphs above, most Activity Calories generated during life probably contribute little to Cardiofitness. 

Researchers long have recognized that only exercise at an intensity above about 7.5 Mets or about 600 calories per hour for an average man contributes effectively to Cardiofitness.  They also have recognized that steady aerobic exercise contributes more effectively to Cardiofitness than does intermittent exercise.  An average man today expends about 950 calories per day or 6700 calories per week of mostly low intensity calories to raise his CFR from the bed rest level of 70 CFR to a sedentary level of 100.   This usual low level and intermittent physical activity of most lifestyles requires 223 physical activity calories to produce a Cardiofitness improvement of each 1 in CFR.   Blair found that only 1390 estimated exercise calories per week of presumably good exercise produced an accurately measured increase of 48 CFR in his high fitness vs low fitness group. This required only 29 activity calories per unit increase in CFR.  Thus specific and presumably serious exercise produced fitness from 8 times fewer calories than did the usual Activity Calories of lifestyle.

Now Measure your Own Cardiofitness:  The above should give you a general idea of what a value a Cardiofitness value in CFR means.  Life Ahead provides a wide range of methods for estimating and measuring the CFR.  The exercise entry pages will provide an average person estimate from the actual usual exercise you enter.  But if you have access to a adequate quality treadmill you can get an estimate by yourself.  Or you can obtain an estimate of your CFR from a variety of fitness measurements now provided in exercise facilities.  See more about measuring your own Cardiofitness.