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Cardio-Respiratory Fitness and Your Health and Longevity: A Scientific Approach
A number of articles have questioned the theoretical and empirical bases for current cardiovascular exercise prescriptions that emphasize the volume of training as the key stimulus causing adaptations in the cardio-respiratory system.
The questioning of the science behind these prescriptions should not, however, be construed as doubting the value of cardiovascular fitness. Quite the contrary is the case.
Cardiovascular fitness is extremely important but it need not take much time to achieve or maintain nor do you have to train with very high intensity.
More and more excellent research is demonstrating the profound effect that modest levels of cardiovascular fitness can have on your health and longevity. . Indeed, if cardiovascular fitness could be sold in pill form, it would be considered the most powerful preventive medication that anyone could buy.
Some New Studies
A new study demonstrates that cardiovascular fitness as measured by a standard treadmill test protocol is health protective for men even in the face of not just overweight but obesity (1).
In this large prospective study, men were tested at one point and then followed up for an average of eight years with records kept of death from all-causes and cardiovascular disease. Men who are fit are at considerably less risk for all-cause and cardiovascular disease mortality then men who are not fit, but more surprisingly - men who are fit but obese are at no greater risk than men who are lean and fit.
In fact, men who are obese but fit are at lower risk then men who are lean but unfit.
One approach for men who are overweight and have difficulty losing weight is to focus more on fitness training and perhaps worry less about dietary restraint.
A greater risk of diabetes has long been associated with both being overweight and leading a sedentary life style. The usual prescription both to prevent and treat diabetes has been weight management and increased activity (and the use of insulin for Type 1 diabetes) with less specific emphasis on fitness.
New data from another prospective study with men using a six year follow-up showed a strong inverse association between fitness again as measured on a standard treadmill protocol and impaired fasting glucose and Type 2 diabetes (non-insulin-dependent; 2). Thus, if you are more fit, you are less likely to get diabetes. Fitness was health protective in the face of other risk factors for diabetes including parental history.
The Nurse's Health Study is a very large epidemiological study that has monitored the activity and dietary practices of almost 73,000 women over an extended period of time and examined the associations between these practices and deaths from all-causes and cardiovascular disease.
Women who are at least not sedentary and modestly active are at appreciably lower risk than their sedentary counterparts. Moreover, there is a gradient of risk reduction that nicely follows the pace that women reported walking. Pace is a proxy measure of intensity. The quicker a woman's usual walking pace, the lower the risk. Brisk walking appeared to confer as much risk reduction as vigorous exercise.
The last point is the key. It appears that there is appreciable risk reduction for men and women when they reach a modest threshold of fitness. There is some increased benefit and protection beyond this modest level, but apparently not much.
Fitness for health should not be confused with fitness for high level performance. If you're not interested in high level performance in this arena, do not do very high intensity aerobic training.
Clarification
Perhaps, Master Trainer has confused some readers about this point. We've emphasized high intensity interval training as a way to markedly improve cardio-respiratory fitness in a very minimal time. If it's very high level fitness you are after, that's one method to efficiently achieve it.
But, you do not have to go to that level of intensity to markedly improve your health and reduce risk. In fact, it may be that some simple, safe, and easy to do variations of these interval protocols (see the February, 1999 issue) can confer the necessary fitness in very brief training sessions.
For example, Ralph Carpinelli has devised a Graded Exercise Protocol (GXP) involving a very brief graded warm-up of several minutes, a two to three minute work period at a designated level (e.g., 70 - 85% of maximum heart rate), and a several minute cool down. The entire GXP takes about 10 minutes and is built around the assumption (not yet empirically supported) that the stimulus causing an adaptation in the cardiovascular system involves simply passing a threshold of intensity and is not dependent upon long duration.
But, even that level of work and structure may not be required to achieve an important, albeit minimal, protective level of fitness. Walking briskly two to three times per week so that for at least two to three minutes your heart rate is sufficiently elevated should work just as well. Thus, you could walk quickly around your neighborhood, or, warm-up and then climb 10 flights of stairs, or find some hills to put in your walking route. Walking hills makes a tremendous difference in the value of your walking.
Here's the caveat. Based on the energy costs of exercise and the threshold for risk reduction, strolling or even conventional brisk walking may not be quite enough of a stimulus for most people for risk reduction. If you can't get to the point where you can walk miles in 15 minutes or less, then walking stairs or hills is the answer.
Remember, it appears that you only need to do a modestly challenging segment on hills or stairs lasting perhaps as little as three minutes after a graded several minute warm-up. For safety, you need to do a cool down that generally involves doing the same activity for several minutes but at a reduced level of intensity.
Prescription
As studies accumulate, we may be able to precisely prescribe levels of aerobic capacity that are associated with different degrees of risk reduction. To look at specific prescriptions, we need to understand how aerobic capacity is measured.
Aerobic capacity can be described in METs. A MET is a multiple of the resting metabolic rate of oxygen consumed per kilogram of body mass per minute (~3.5 ml.kg-1.min-1). Fitness revolves around your ability to consume oxygen.
Based on existing data, I've taken some of the first steps toward developing these prescriptions.
Here's how I've measured protection (risk reduction) and corresponding MET levels.
I looked at prospective studies from the Institute for Aerobics Research with men and women that examined fitness as measured by time on the Balke treadmill protocol and then looked at the association of that time years later with death from heart disease, cancers, and all-causes. I then took the time that corresponded to the group just above the least fit people, a level that affords some protection, and then the time for the most fit men and women.
I then reviewed data that showed the estimated VO2max and MET values for those times on the treadmill protocol. Thus, I have empirically derived estimates of MET values that need to be achieved to afford minimum and maximum protection.
For men the data suggest that perhaps the ability to reach a MET level of nine
(31.5 ml.kg-1.min-1) at the point of maximum oxygen consumption confers some protection. It also appears that protection may start to asymptote at perhaps 13 to 14 METs (45.5 to 49 ml.kg-1.min-1).
For women, the minimal level of protection may be 7 METs (24.5 ml.kg-1.min-1) and the top level may be about 11.5 METs (40.3 ml.kg-1.min-1)
This may mean that if you are a man and you are interested in some minimal protection, you would only need to train to the point where for two to three minutes you can sustain a level of about 80% of the nine MET level (7 METs), at 80 - 85% of your estimated maximum heart rate. If you could not safely train at 7 METs, you would simply start at an easier point and work you way up during the course of a series of workouts.
If you are a man and wanted maximum protection, you would have to train to the point where for two to three minutes you could sustain a level that is about 80% (11 METs) of the 13 to 14 MET level at 80 - 85% of your estimated maximum heart rate. The same process of working toward that goal can be used.
Women can pick the corresponding levels. For achieving minimal protection, women need to train at a level of about 5.5. METs for two to three minutes at 80 - 85% of your estimated maximum hear rate and for achieving maximum protection, training at a little over 9 METs for two to three minutes at 80 - 85% of your estimated maximum heart rate is the prescription.
What Do These Levels Mean?
Nine METs corresponds to about level three on an Air Dyne and 13 to 14 METs is slightly more than level 5. About 80% of these levels is 2.5 and 4. Level 3 expends about 12 calories per minute and slightly more than level 5 expends about 18 calories per minute.
Correspondingly, level 2.5 is about 7 METs and expends 10 calories per minute and 11.5 METs is about level 4.25 on the Air Dyne and expends about 14 calories per minute.
Certainly, the minimum level of protection that frankly brings the biggest bang for the buck (the biggest benefit is going from unfit to modestly fit) is reachable by the vast majority of people without much effort.
This means as a man that even if I was interested in absolutely maximizing protection - 15 METs capacity, about level 6 on the Air Dyne - I would only have to train to the point where after a warm-up I could ride my Air Dyne at about 85% maximum heart rate and at about level 5.0 (about 85% of this top level) for three minutes. I would then cool down.
That would be the extent of my workout on the Air Dyne and correspondingly on other cardiovascular pieces. I would only need to train to this level two or three times per week.
There's little data to support more frequent training.
Here's another example. Running a mile expends about 100 calories. So, it appears that you could be sufficiently fit from running if for as little as three minutes you can manage an 8 - 10 minute-mile pace at about 80% of your maximum heart rate.
Heart Rate, Inc., the company that makes the Versa Climber, also has data showing relationships between work levels, caloric expenditure, and oxygen consumption.
To reach a level that would afford me maximum protection, it appears that I would need to get to the point of doing a climbing pace of 150 feet per minute for about three minutes.
But, I could obtain minimal but important risk reduction benefits if I could reach a pace of only about 100 feet per minute.
Here are some more data about walking, the most common activity that is recommended and many people do.
As you'll see, you may want to separate walking to socialize or for simply getting some activity and expending some calories from walking to increase or maintain fitness. Walking at any pace can satisfy the first goals and take you out of the "completely sedentary" category but that won't do for meeting fitness goals.
Up to about a 4 mile per hour pace on a flat surface, the MET equivalent for walking is about equal to it's pace, i.e., 3.5 miles per hour equals about 3.5 METs.
As you walk more quickly, walking becomes less biomechanically efficient so the energy cost increases.
Walking at a 4.5 mile per hour pace (13:20 minute miles) on a flat surface is equal to about 5.7 METs and walking at a 5.0 mile per hour pace (12:00 minute miles) is equal to about 6.9 METs.
However, walking at a 3.5 mile per hour pace but up a 5% grade is equal to about 5.9 MET's, the same pace at a 10% grade is about 8.3 METs, and a 15% grade is 10.7 METs. If you can't find hills to walk, the best suggestion is to warm-up and then walk up stairs for about three minutes.
For most people, there really are no more excuses about time and the problem of getting to a gym. If you work in a large office building or live in a large apartment house, you have a built in aerobic training facility.
Simply warm-up by walking around the halls and then climb the steps for three minutes, and finally do some easy walking for a cool down. You can progress in your stair walking by slightly increasing your pace over a series of workouts.
While the MET equivalents I've given are accurate for the different exercises, the efficacy of the specific short GXP's that would involve these exercises at different levels needs to be further researched.
However, what may surprise many people is that reviews of the aerobic exercise training research show lots of evidence for the importance of intensity and frequency of training, but very little evidence that any specific duration of training is required.
Rather it appears that simply passing a designated level of intensity for a short time period is the critical stimulus for causing adaptations in the cardio-respiratory system. Interestingly and quite ironically, this was one of the conclusions of the earliest aerobic training research done more than 30 years ago.
My Personal Approach
It's true that not all the data is in to support the benefits of these short, very prescriptive protocols.
However, since I believe the approach is on the right track and given that my main goal with cardiovascular training is maintaining health, I'm seriously reconsidering how I do this training.
Clearly (and quite ironically), from a health perspective, there's no reason to kill yourself with cardiovascular training if you're after health and not top performance.
This isn't an original thought. Drs. Ken Cooper, Steve Blair, Andrea Dunn, Abby King and others have been saying this all along.
You won't get much if any protection from just strolling or sitting on the exercise bike and peddling with no resistance but you do not have to go very hard or very long to be practicing good preventive medicine.
It's also true that an excessive volume of aerobic training or very high intensity aerobic training can compromise strength training. However, does anyone seriously believe the kind of brief, modest fitness training just described would result in anything but beneficial outcomes?
So, what does this mean for me and perhaps for you?
For the past 30 years, most of my cardiovascular training has been at a very high intensity (you could say crazy pace) that obviously had some compromising effects on strength gains. With great hindsight, I can see that it never made any sense because I wasn't interested in being a competitor in short distance or endurance events.
In addition, training the cardio-respiratory system at such incredible levels of intensity as I always did can have some real health compromising effects.
Suffering a cardiac event is certainly one sadly ironical possibility! Fortunately, even when training at close to 100% maximum heart rate, I never experienced such an event. I've been lucky.
The other more subtle problem is that adding very high intensity cardiovascular training to very hard weight training has to periodically play havoc with your immune system. So, again, in the name of health, I've been increasing my health risk!
I'm certainly curious to see what happens when I adopt this much saner, healthier, and scientifically based approach.
My basic plan is simple. I'll do a graded warm-up of several to five minutes and then either with a three-minute steady state or series of short repetitions and intervals, I'll keep my heart rate at 80 - 85% of maximum using the Karvonen estimate (see below). Then I will do a several minute cool down.
I'll do this basic GXP two to three times per week using the Air Dyne, Versa Climber, and Concept 2 Rower. Occasionally, I'll use a Life Cycle or simply find about 15 flights of stairs to climb.
I'll continue my every day walking because it is pleasurable, provides some activity, expends some calories, and allows me to have more latitude in what I eat.
As a final note, I consider this one of the most important articles I've done for Master Trainer because of its wide health implications for many people. I want to thank Ralph Carpinelli for feedback on drafts of this article.
Training Heart Rate
The Karvonen method for calculating training heart rate more closely matches oxygen consumption at a given percentage. So, 85% Karvonen is about 85% of maximum oxygen consumption. There are, however, some discrepancies at different levels but for figuring training heart rates, those discrepancies aren't critical.
To use the Karvonen method, you need to have good estimates of your maximum heart rate and your resting heart rate. Age predicted maximum heart rate may not be the best estimate of your particular maximum heart rate. You may need to take a MAX test in an appropriate laboratory setting with all the necessary safety measures to determine your maximum heart rate.
With the Karvonen method:
Training Heart Rate = (Max HR - Rest HR) x (%Training Intensity) + Rest HR
If a person had a Max HR of 180, a Rest HR of 60, and wanted to train at 80% intensity, then:
(180 - 60) x (.80) + 60 = 156.
Here's another example for a person with a higher Max HR (190), a lower Rest HR (50) and desiring to train at a higher level of intensity (85%).
(190 - 50) x (.85) + 50 = 169.
Notice that with the Karvonen method, the training heart rate is higher than simply taking a percent of estimated maximum heart rate.
Here is one final point about training heart rate and the effectiveness of the GXP that is already suggested by research.
You need to do your graded warm-up so that at the end of the warm-up you are right at the threshold of your training heart rate. Then you want to be at the training heart rate target for the entire three minutes. If you only reach your target heart rate range at the end of the three minutes, this does not appear to be an effective stimulus for inducing cardio-respiratory fitness.
References
Chong, D.L., Blair, S.N., Jackson, A.S. Cardiorespiratory fitness, body composition, and all-cause and cardiovascular disease mortality in men. Am J Clin. Nutr.1999; 69: 373-380.
Wei, M., Gibbons, L.W., Mitchell, T.L., Kampert, J.B., Chong, D.L., Blair, S.N. The association between cardiorespiratory fitness and impaired fasting glucose and Type 2 diabetes mellitus in men. Ann Intern Med. 1999; 130: 89-96.
Manson, J.E., Hu, F.B., Rich-Edwards, J.W., Colditz, G.A., Stampfer, M.J., Willett, W.C., Speizer, F.E., Hennekens, C.H. A prospective study of walking as compared with vigorous exercise in the prevention of coronary heart disease in women. N Engl. J Med. 1999; 341: 650-658.
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