The Relationship Between Muscular, Cardiovascular, and Metabolic Adaptations: An Opinion
by M. Doug McGuff, M.D.
Every month Dr. Richard Winett sends me a copy of his publication Master Trainer. I always enjoy reading his newsletter, it usually has a lot of valuable information and even when the information is not valuable, it challenges my beliefs and forces me to examine the underpinnings of those beliefs. The Master Trainer places a lot of stock in peer-reviewed literature, so it usually contains references to recent articles that allow me to assess how close the scientific community is coming to understanding what has been known by a small minority of people for decades. Not to sound cocky or disrespectful, but if I waited for the peer-reviewed literature to catch up this minority, I would probably be long dead. If I applied only what the peer-reviewed literature said was true about exercise, I probably would have spent my time running marathons back in the 1970's and would now be too crippled to do any form of exercise. Thank goodness I was instead reading Arthur's training bulletins and getting a healthy dose of skepticism in regard to peer-reviewed literature.
Don't get me wrong. I have immense respect for the peer-review process. If it enforces the scientific process, it can give us certainty in regard to our logical inductions or point out how we were wrong. Many times the peer-reviewed literature can provide astounding information whose significance is missed by even those doing the research. I will give an example of this later. The August 2000 issue of Master Trainer has an article entitled "Strength Training Takes Center Stage". Dr. Winett points out the numerous articles in the recent literature that tout the health benefits of strength training. He notes how in the past, the scientific community touted endurance training and discounted strength training as a means to health... "Anaerobic exercise such as strength training was seen at best as unnecessary and more than likely dangerous for health and safety". I can attest that this was always what I was told. Not only was I not doing exercise for my heart, I was doing a form of exercise that was putting a strain on my heart and was clogging my arteries. Dr. Winett continues... "But many of us, again myself included, may have rationalized our strength training by saying: 'But, I also do things for my health such as my aerobic training". Dr. Winett goes on to offer the current scientific evidence for why we don't have to make that rationalization anymore. That now, aerobic training can be seen as something that is an add-on to the more fundamental exercise that is strength-training. In Ultimate Exercise Bulletin 1 I make the case for why this rationalization need never occur.
How Did Aerobics Get Mistaken As The Best Form of Exercise?
The actual history of this question is actually quite convoluted and involves things such as Kenneth Cooper, MD, as well as sport and the fashion of the time. However, there are some fundamental factors that contributed. The first factor is confusing association and causation. Improved physical conditioning is associated with better health to a large extent because intrinsically unhealthy people can't or won't exercise. When you study the effects of exercise you require large numbers of subjects who will exercise. You automatically weed out the unhealthy which skews your data. Improved functional ability also improves overall well-being and has positive effects on many markers of health. I do believe that proper exercise improves health and longevity but to a lesser degree than the data would suggest and that longevity is actually improved through better functional ability rather than improved intrinsic health. The second contributing factor is reliance on testing tools. An old saying describes it best: "when your only tool is a hammer, the whole world becomes a nail". The main testing tool available was the V02max test, which is a test geared towards lower intensity forms of exertion. In order to draw a correlation between exercise and health, you have to have a measuring tool that can produce tangible results that can be compared against health outcomes. In essence, the question was framed to fit the existing test, rather than trying to find a test to fit the question. Current definitions of fitness still are tied to what test is currently the rage. The last contributing factor is that the favored test (V02max) performed poorly at high levels of exertion (in my opinion). When the really hard work began (as in resistance training) V02max appeared to fall off, so it was assumed that since V02max correlated with cardiac output that resistance training decreased cardiac output and was thus a poor form of cardiovascular conditioning. The fundamental problem here is mistaking a metabolic adaptation for a cardiovascular adaptation. Improved cardiac condition can have many different specific metabolic adaptations linked to it, with improved V02max being only one of many specific metabolic adaptations. You can have great cardiac condition linked to largely anaerobic metabolic adaptations (for example Carl Louis or Ben Johnson as sprinters) versus cardiac conditioning linked to aerobic adaptations (such as Tour de France Winner Lance Armstrong).
Resistance Training: The Best Cardiovascular Workout Possible.
Ken Hutchins has stated it more clearly than anyone: "The only way you can get at the cardiac or vascular system is by performing mechanical work with muscle. The higher the quality of muscular work, the better the cardiovascular stimulus". However, V02max has been noted to fall during high intensity resistance training, and since V02max is supposed to track cardiac output, then resistance training must cause cardiac output (CO) to decrease, right? Well, you would not believe the explanations that have been invented to explain this phenomenon. Rather than assuming something might be flawed with the test at high levels of exertion, there was a rush to explain why weight training caused CO to decrease. Here are a list of examples I have been told.
1. The high degree of muscular tension traps venous blood and results in decreased venous return to the heart. In my opinion this is makes no sense. The venous system is a passive blood holding system. The major way blood is moved back to the heart is through the massaging action of the contracting muscles. Increased muscular tension produces more force on the wall of the veins and increases venous return. Increased venous return to the heart increases myocardial stretch and thus myocardial contractility which increases cardiac output.
2. The high degree of muscular tension exerts pressure on the arterial system which increases afterload (the resistance the heart must pump against) and thus decreases CO. The pump that occurs with weight training further constricts these vessels which contributes to the above mechanism. It has been my opinion that the pump exists because of the increased cardiac output and increased blood flow into the working muscles.
3. The severity of high intensity resistance training causes an outpouring of catecholamines (adrenaline-like substances) which stimulate a flight or fight response. These catecholamines causes increased arterial tone and blood pressure which increases afterload and thus decreases CO. It has been my contention that resistance training does result in an outpouring of catecholamines, but the effect of this is the exact opposite of what is stated above. There are different types of receptors that catecholamines bind to. In the heart, Beta-1 receptors bind catecholamines and result in increased heart rate and contractility which increases cardiac output. In the lungs and vessels supplying working muscles there is a predominance of Beta-2 receptors. Catecholamines that bind here cause smooth muscle relaxation. This results in bronchial dilation (so you can increase ventilation) and dilation of arteries in the working muscle which decreases peripheral resistance or afterload which also results in increased cardiac output. Alpha receptors predominate in the blood vessels supplying the gut. This causes vasoconstriction which shunts blood from the gut to the working muscles. This is why your mom said not to swim until an hour after you eat. It seems good old mom may have understood more about the relation of muscular work to blood flow than the exercise physiologists trying to explain away the deficiencies of V02max.
A quote from Dr. Winett in the October 1997 issue of Master Trainer "More on Resistance Training and Cardiovascular System Impacts" encompasses all of these arguments.
"It appears that the nature of strength training, relatively slower repititions, very high muscular tension, results in limited venous return of blood to the heart, i.e. limited 'preload', which limits stroke volume. These conditions elevate heart rate. Movements with high muscular tension also create increased 'afterload', which is impedance to ventricular emptying. Increased afterload results in an increased workload for the heart, thus having a negative influence on the heart's performance. During strength training, as supported by the blood samples in this study, there was a great stimulation of the heart by the catecholamines and increased afterload from intramuscular pressure which produces occlusion of circulation in the muscles that are being exercised."
The above statement, while an eloquent argument, went in complete contradiction to everything I learned about human physiology. This flew in the face of logic. The physiology of catecholamine receptors aside, what sense would it make for blood flow to decrease to a working muscle? Even if the work is anaerobic, the need for blood flow does not just rest on oxygen delivery. C02, lactic acid and other waste products must be removed. Arguing from logic does not prove adequate nowadays so I have been on the lookout for an article that might address the question. To answer the question, you would actually have to directly measure hemodynamic changes during resistance training.
Well, after 3 years of searching, I finally found an article that uses central catheter monitoring during resistance training so that we can see directly what is going on during a resistance training workout. The article is entitled Hemodynamic responses during leg press exercise in patients with chronic congestive heart failure. Am J Cardiol 1999 Jun 1;83(11):1537-43. This study showed a significant increase in heart rate and mean arterial blood pressure (this was expected). It also showed an increase in diastolic pulmonary artery pressure (this is a measure of venous return to the heart and is the opposite of what had been argued to me and supports my contention of increased venous return). Most importantly, there was a decrease in systemic vascular resistance, and increased cardiac index (cardiac output per unit of body size) and increased left ventricular stroke work index suggesting enhanced left ventricular functioning. These findings are in complete opposition to the arguments above as to why strength training is a poor cardiovascular stimulus. The problem is the measuring tool of V02max is worthless for detecting cardiovascular changes at high levels of exertion. This data is highly significant. I do not know if the researchers themselves know how significant this is in light of the exercise physiology community's attitude toward resistance training. In my opinion, this is very powerful evidence that resistance training provides an excellent cardiovascular stimulus, better than other forms of exercise, with many other benefits attached that cannot be had with any other form of exercise.
Metabolic Conditioning is Very Specific
Cardiovascular conditioning is achieved by performing mechanical work with muscle. Different forms of mechanical work will result in different metabolic adaptations. The cardiovascular conditioning will always occur relative to the quality of muscular work, but different metabolic adaptations occur based on the exercise protocol at hand. The problem occurs when we think that only a particular metabolic adaptation correlates with cardiovascular condition. This has been the problem with V02max and other forms of fitness testing. Only that specific metabolic adaptation is accepted as a marker of cardiovascular health, when in fact any number of metabolic adaptations could have been attached to the cardiovascular improvements. You could have the largely anaerobic improvements of the puke-on-the carpet HIT enthusiast. You could have the metabolic changes that come from a specific interval protocol such as the Tabata Protocol, or it could be a more steady state activity. Whatever you arbitrarily decide is "good" and track relative to health outcomes will prove to be what is good.
In the October, 1997 issue of Master Trainer Dr. Winett writes: "According to Tabata et al. articles and personal communications (July 1997), this protocol works so well because it maximizes oxygen consumption. The rapid movement with high intensity in cardiovascular exercise is simply different form high intensity resistance training probably because the preload is not attenuated and muscle tension is not high...In addition, the very short rest period between bursts , assures oxygen uptake increases throughout the protocol, reaching the highest level at the end of the protocol...This fits the bill for effective training; a high percentage of V02max produces the biggest gains in V02max".
In the August, 2000 issue Dr. Winett writes about his experience with a new aerobics protocol called GXP which is modeled after another fitness test called the GXT (I assume the graded exercise test). After years of interval protocols such as the Tabata protocol and daily walking Dr. Winett is upset to learn that his performance on the GXP is substandard. "When I did the GXP correctly, it was apparent that my fitness level was good but not all that exceptional... So, why with all my years of prior interval training and then doing the super Tabata protocol was I not all that fit?". Dr. Winett then speculates.. "More than likely with the Tabata protocol, heart rate may not track oxygen consumption. Basically, the protocol entails anaerobic bursts. A high heart rate with that protocol as with weight training may simply show a rather extreme response to a physical stressor".
Reading these two quotes is an interesting exercise. First the Tabata protocol is the best thing since sliced bread for improving oxygen uptake and thus cardiovascular health. Then later, with the Tabata protocol perhaps heart rate doesn't track oxygen consumption. I would suggest that the reason his fitness appeared mediocre when trying the GXP is that he changed his test that defined what good cardiovascular fitness is. I would bet that after a few months of GXP his fitness as defined by the Tabata protocol would be mediocre at best. I have come to appreciate that muscular conditioning is fairly general and cardiovascular conditioning is fairly general. However, metabolic conditioning is highly specific. I will offer a couple of examples from my personal experience.
When I was in the Air Force, we had to pass a yearly cycle ergometer test that was supposed to confirm our aerobic fitness. We had several very fat deconditioned officers in my unit who learned how to subvert the test. About 4 weeks before the test they would practice on the same type of ergometer using the exact 10 minute protocol used for testing, this was done 2-3 times per week. These officers, who by any standard of fitness were in horrible shape, passed with some of the highest scores. At the same time we had several highly competitive 10K runners. Being confident about their level of fitness, they continued to run and simply showed up on test day. Most passed with marginal marks and a few even failed. They did not fail because they were out of shape, they failed because the did not prepare their metabolism for a specific test. Road runners who train on a treadmill in the winter noted that they seem in horrible condition when they return to road running. This is because slightly different body mechanics result in specific metabolic adaptations.
A more recent example drove this home to me. I recently returned to my sport of BMX. It is a form a off-road bicycle sprint racing that lasts about 45 seconds per race. When I first started racing I had been doing nothing but HIT/SuperSlow. At that time I noted some initial trouble with my "wind" as I would be breathing quite hard at the end of a race. Within 2-3 weeks, I was doing much better. Then, I started to question if some form of metabolic or aerobic conditioning was necessary for my sport. I then gave a trial of doing the Tabata Protocol (20 seconds maximum sprint-10 second respite for 6-8 bouts). What I found was shocking. My "wind" became much worse. It seemed that I started to breath like a fish on the dock about halfway through the race. It seems that I was becoming conditioned to needing that 10 second respite after 20 seconds of hard work. I then changed my bike work to something specific to the requirements of my sport. I included full laps on my practice sessions, or if I couldn't get to the track I would do 45 second intervals. Remarkably, my metabolic condition is now fine-tuned to my sport.
Metabolic Adaptations Up and Down-Regulate Quickly
I have found that strength adaptations are very well preserved and deteriorate slowly. Strength in my more established clients persists despite several weeks of layoff. Metabolic adaptations deteriorate quickly. If you go to Denver, you will note shortness of breath with exertion, but within a couple of days you will adjust. If you go back to sea-level for a few days and return, you will be back to square-one. This makes economic sense, metabolic adaptations involve less raw materials than muscular adaptations and are easier to assemble/disassemble as needed. Further, adaptations can be made to very specific degrees depending on the situation.
