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Please re-read my post and you will no doubt see that I made mention to weight training in the "off" week. It is my opinion that the most successful weight loss programs incorporate strength training in addition to aerobic workouts. This is the rationale of circuit training; combining endurance with progressive resistance has shown greater benefit that either cardio or weight training alone. However, attention has recently been placed on whether or not alternating days (one day weight training, the next day cardio) will allow for full muscle recuperation. My first post is one of the attempts to counter this phenomena and provide for a more effective weight loss program. However, doing cardio alone and just alternating weeks will not be as effective as continually scheduled cardio workouts. That is something I think we can agree on.
However, I think you have mistakenly confused physiological adaptation with muscle neurology adaptation. It takes increased demands on muscle tissue in order to increase the workload of that muscle as well as it's capacity for work. But increasing muscular adaptation is not the way to go as far as fat loss is concerned, nor is it the way to go insofar as muscle strength or muscle building is concerned. In these regards, the more the muscle adapts, the less work it is performing as a whole. This results in loss of muscle mass. Wouldn't you want to lose fat weight rather than sacrifice muscle tone?
The greater the amount of cardiovascular exercise that is done (with respect to degree) the higher the likelihood of muscle loss. As AML has effectively pointed out, loss of muscle mass can actually increase the amount of fatty tissue in the long run. Muscle mass loss caused by doing only cardio is a direct result of applied laws of physics; a larger body doing the same amount of exercise as a smaller body will have greater resistance to the movement. So the adaptation that occurs is physiological in the sense that the body will reduce it's mass in order to accomodate to the extended workload. In doing so, it selects non-essential tissue (in other words, tissue that is not an organ and not required for minute-to-minute life sustainment) and decreases the size (mass) of this tissue with respect how rapidly that tissue can both regenerate and adapt. Muscles can gain or lose size rather rapidly due to their adaptation capability and the fact that muscles have extensive blood supply. Increased oxygen demand, pH changes, and metabolic needs, if occuring as a result of endurance exercise will result in decreased muscle mass. The muscles then are primed to do endurance work and tend to not have a high resting metabolic need. Therefore, these muscles truly burn fat almost exclusively while doing cardio, but not when the person it at rest. If this were not the case then professional powerlifters and bodybuilders would benefit like the rest of the population from extended cardio. However, that is not the case. The longer a person performs cardiovascular exercise (duration and frequency), the greater the demands of the muscle to adapt to this workload. Thus the muscles lose size since the body will attempt to lose weight and reduce extra work. However, alternating exercises to include both cardio and strength training is preventing muscle accomodation to endurance exercise by way of limiting it's ability to adapt. Increasing muscle tone by weight training will increase the muscle tone through forcing a movement without allowing for sufficient adaptation as long as intensity and variation are incorporated.
Here is why an endurance muscle (from only cardio) is not optimal for fat loss: If adaptation occurs within a given muscle, then that muscle will recruit less of the muscle fibers to perform the work...the end result being accomodation to decreased intensity. This is called selective myoneural synapse inhibition. It is caused by doing a repetitive endurance exercise increasing the frequency or intensity either naturally or progressively rather than performing short bursts of muscular contraction with a target percentage of maximal work done. This will happen regardless of whether we are talking about weightlifting or doing cardio. You HAVE to change the variation in order to increase metabolic demands. This is precisely why there are overweight people in GREAT shape who are teaching aerobics very good cardiovascular shape but unable to lose the problem fat. Remember that the body will drop weight in order to allow for physiological adaptation to accomodate for the work being done, but it can only do that to tissue that has an adequate blood supply! Problem fat areas on both men and women respectively are primarily composed of white fat...called "white" because it visually appears nearly devoid of blood vessels. This is why problem areas are tough to reduce...they do not have much blood supply so therefore the tissues are not very metabolically active. Therefore increasing cardiovascular endurance is not likely to decrease the amount of problem areas as well as was previously thought. Yes, over a very long period of time, this can help reduce fat, however, as I mentioned before, there are overweight people who are in excellent cardiovascular health teaching aerobics classes, and so for these people, cardio has NOT been their best answer. I would suspect that a very significant percent of the population has the same problem...inadequate blood oxygen carrying capacity. So for these people as well, cardio alone is not effective in the long run. Increasing the endurance demands of muscle tissue is not the best way to go IF there is no weight training to supplement. A muscle primed to achieve short high-intensity work in the way of strength training is primed to burn more calories than a slender endurance muscle. This is because the larger strength-oriented muscle will have a greater metabolic need than a slender muscle primed to do endurance work.

In respect to the mentioning of aerobic capacity as the best means of losing fat, I beg to differ for a few reasons. The oxygen carrying capacity of one person is NOT similar to that of all other people. This is a direct result of amount of vasculature and also other individual reasons. If you have more fatty tissue, you have more blood vessels. The more blood vessels a person has, the tougher it is for their lungs to oxygenate their blood effectively to send oxygen to all cells in need. The result is necessary tissue gets the oxygen first (such as brain, heart, muscles, bones, etc. etc. and finally fat tissue at the bottom of the list). So essentially, very little oxygen is available for fatty tissue oxygenation. So the primary concern is that you have to either be doing EXTENSIVE cardio work AND have a very good oxygen carrying capacity of your blood, AND/OR you have to have factors that would increase fat metabolism while NOT performing cardio. The best and only way this can be performed in my opinion is with the inclusion of weight training in addition to cardio...of course, unless you happen to have a high metabolism to start with and also have exceptional oxygen carrying capacity of the blood. It's too much guesswork and expense to try and determine this. Better to just add weight training to a cardio regimen in order to exact the most dramatic and rapid changes.

I'm sorry to be so technical, but I think I was called out rather than questioned specifically. I hope not to write a book next time. :)

[This message has been edited by paper clip (edited 07-16-2001).]
"There is a ton of literature to indicate that an aerobically trained muscle burns more fat at any given muscle load. If you want to burn more fat, increase the mitochondria in your muscle and this is accomplished through aerobic exercise. Exercise physiology 101"--- Of course it does, there is no dispute in that. However, you might consider increase lean body mass index and muscular metabolism. Clinical experience and physiology laboratory data as well as individual experiences have suggested rates are different, slanted in favor of larger lean body mass indices. But yes, you're right, there is no comparison between short bursts of high intensity and extended constant exercise periods in terms of immediate caloric expenditure. And remember, we're talking about general fat burning at all times of the day, not just during exercise exertion.

"As for oxygenation of blood, unless someone has compromised lung function or has anemia or some other blood condition that compromises Hb binding with oxygen, the blood gets oxygenated just fine."---Yes it very well may, but if there is peripheral resistance to proper blood flow to ALL areas of the body, preferentially in persons with high white fat amounts, then cardio efforts are basically doing things the hard way. Rather cardiac muscle itself burns energy as a result of increased peripheral resistance. The trick is to increase muscle size so that the fat burning process takes place on a more continual basis rather than having a slender muscle that would, by physical limitation of matter, not be able to burn fat to the same degree when the person is at rest. This is reiteration...just understand that the capability of lung capillary exchange and oxygenation of blood does not necessarily mean that all tissues will be properly oxygenated...even muscle make this claim is skipping a few physiological steps. The more resistance there is (body size, fat in particular) the less oxygen is provided for ALL tissues...the result is inefficiency and diverted blood pathway. Since an overweight person has more vasculature, there is more blood tied up in other parts of the body, which can result in cardiac increased workload to distribute the oxygenated blood in more of a timely fashion.

"What is a limitation is the heart's ability to get blood to the muscle, but we are talking maximal capacity here, not submaximal conditions."---If this were the case there would be little need in "resting" cardiac examination to evaluate diastolic measurements. Yes, heavy exertion can obviously aggravate hearts susceptible to ischemia and compromised function. But if submaximal exertion did not have a cause and effect with relation to peripheral resistance then there would be no such thing as exercise-induced myocardial infarction. Many of these people who have heart attacks while jogging have them without apparent serious strain. So the effect of submaximal exertion does, in fact, cause physiological cardiac changes.

"There is no literature to date to definitively say that weight lifting combined with aerobic exercise is best for weight loss."---well this kind of depends on what your definition of literature is. NO LITERATURE is incorrect. No literature that convinces you is more accurate, I would believe. No, science has not reported any conclusive LONG TERM studies of the effects of exercise and weight loss of either weight lifting or aerobic activities, but this is likely to be a result of research project limitations. However, we do not HAVE to have conclusive proof of a certain specific when the variables making up that specific are well-grounding in what is well-known. Sort of like we don't have to have scientific proof that the sun will rise, yet it does anyhow. We can use deductive reasoning and have a sufficient measure of comfort.

"Overall, exercise alone has not demonstrated very large results in terms of fat loss."---I'm not following you suddenly. You stated vigorously before that 'exercise alone has not resulted in very large amounts of fat loss' I'm not sure which stance you are ultimately taking, to be honest. If you would, please let me know which you feel is most appropriate to your personal viewpoint. So while there may not be enough data to convince you that weight training is an important part of a weight loss plan, there is apparently data that you are providing that suggests a contradictory opinion to your statements. Very true, exercise alone doesn't seem to cut it. Diet must be taken into account as well as other factors such as genetics and exercise type/quality. People do not seem to want to know the truth that the best way to lose weight is by varied exercise, diet modification and just plain hard work. Such studies are not pursued actively in that this is what is widely regarded as the rule rather than the exception. However, as slim as the data might seem to be, few people will deny that exercise and diet modification are mainstays in the way to lose body fat.

"It is true that under certain conditions, weight training can effectively maintain or increase muscle mass. But, whether this promotes greater fat oxidation or not is unknown."---the scientific research literature may not show this directly, but then again, the same could be said for the discrepancies with so much of physiology. Even professionals disagree on a daily basis. Essentially, nothing is conclusive in that everyone is different and what works for one person may not work for another. Research project failures-to-agree are sometimes the result of protocol factors, not can't watch what everyone eats all the time nor measure how their body will respond to periods of exertion and/or rest. However, greater body weight in relation to lean body mass results in a better O2 uptake as measured by Krogh metabograph than persons with less lean body mass. Therefore, they will LIKELY have a higher resting metabolism. This may not be the proof you want, but it is a sound physiological model.

"During submaximal aerobic exercise, type I fibers are primarily recruited. As these fibers fatigue over time, more and more type II fibers are recruited. Likewise, as the intensity increases, more type II fibers are recruited. But type II fibers are not aerobic muscle and burn little fat you say? True, but by recruiting them, over time they adapt by becoming more aerobic and thus, will burn more fat."---Of course, mitochondrial need will result in degree of metabolism of nutrients, that's a given. However, mitochondrial fatty acid oxidation will be dictated more by activity level in red muscle fibers. Besides, red muscle fiber by nature has a higher ratio of mitochondria. The high concentration of myoglobin as well as high innervation frequency will dictate that this muscle type functions in the way of fat burning primarilly WHILE engaging in endurance exercise. Whereas on the other hand white muscle fiber has a high resting tissue metabolic need on the basis of it being an anaerobic tissue due to low concentrations of myoglobin. So just to "exist" in it's state of increased muscle mass, maintenence metabolism is going to be higher than in a less muscle mass individual. Maybe you are referring (by mention of submaximal contractions) to dynamic endurance training. I do agree that cardio of this type can be beneficial for fat loss, especially when combined with strength training in that the alteration of exercise type itself warrants muscle signal change. Since the body is constantly trying to find a shortcut to workload and find the easy way out, exercise variation in both type, intensity and duration will have ultimately burn more calories due to the fact that the body is having to work harder in trying to adapt. The more it adapts in this case, the more stable it will become in regards to muscle metabolism. However, since we are referring to the individual as a whole rather than on the scale of muscle fibers, I refer back to the physiological model I mentioned above of higher resting metabolism in persons with greater lean body mass.

"When it comes to weight loss, the amount of fat burned during exercise plays a relatively insignificant role."--I couldn't agree more. One hour of the day (or less) in activity does increase caloric expenditure, but with an increased muscle mass the resting metabolism is higher and therefore fat burning tends to take place effectively in the hours and days following the weight lifting. The same cannot be said for typical cardio exercise that does not involve maximal or near maximal burst intensity.

"Rather it is the chronic negative energy balance that will allow fat loss. Becoming aerobically conditioned simply allows one to burn more calories during each exercise session"---Again, I agree, the calorie burning takes place during the exercise. So it would be of great benefit to add strength training to your regimen to allow for greater resting metabolism and in effect, weight loss to take place on a hourly basis throughout the day.

"And if cardio exercise is not effective for weight loss or at least helping to maintain a healthy weight, then why are there so few "overfat" endurance athletes?"---Keep in mind that genetics plays a large role in determining who is competitive as well as who chooses that as a lifestyle or profession (after all, you don't see many skinny men playing offensive line for professional foodball teams, although many wish they could). In all truth, both the muscular (mesomorph) and well-rounded (endomorph) will have to do more work in order to do the same exercise performed by the ectomorph or slender bodied person. Think about it this way, which uses more gas to drive one mile---a honda or a mack truck? The distance is the same, but the energy expenditure is not. The truck burns more gas to do the same job. Larger bodied individuals do not often choose to perform this type of competitive activity since their natural body type is not as accomodating as that of the slender build types. However, for sprints and dashes take a look at these athletes. They possess fantastic physiques with very low bodyfat levels (most of them work out with weights) but many do not even run a mile on a regular basis! I would personally rather have the muscular definition of a sprinter than a narrow-framed and tired looking endurance runner...but that is just my personal choice. :) Back to the nature, less work means less exertion for the same activity for slender persons and therefore full exertion can in these cases result in greater accomplishments (in timed running for instance). Of course, there are exceptions to this rule. But the competitive endurance athletes are typically people who can do "X" amount of work with the least amount of energy expenditure, to answer your question.

It seems like you are on the right track, educationally speaking, in much of what you are saying and I personally think that we have more to agree upon than previously thought. However, there is no shame or anger in simply disagreeing. We can debate all day long and at the end of the day we still have our own theories. Besides, neither of us can post everything we know in one or two messages (or even a thousand messages :) ).

Take care and good luck!

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