Arthur Jones, the inventor of Nautilus and MedX,  said the following during an interview with Stephen Langer, MD on the show Medicine Man :

“…the lifting of weights is so much superior for the purpose of improving the cardiovascular condition of a human being that whatever is in second place is not even in the running, no pun intended. That is to say, running is a very poor, a very dangerous, a very slow, a very inefficient, a very nonproductive method for eventually producing a very limited, low order of cardiovascular benefit.

Any, ANY, result that can be produced by any amount of running can be duplicated and surpassed by the proper use of weight lifting for cardiovascular benefits. Now I realize that here are hundreds of thousands, perhaps millions of people in this country who
don’t understand that, who don’t believe that, who will not admit that. Now these people are simply uninformed. Certainly, it’s possible to run with no benefit, it’s possible to  weight train with no benefit. I’m talking about the proper use of weights and properly applied, weight training will improve your cardiovascular benefit to a degree that is impossible to attain with any amount of running.”

When properly performed, strength training meets all the requirements for cardiovascular conditioning. Assuming that one trains intensely enough and allows no rest between exercises, HR can be elevated to a tremendous degree and maintained throughout the workout. Some of the highest HR’s on record were achieved by subjects performing high intensity strength training during the project: Total Conditioning at West Point Military Academy. Cadet’s maintained HR’s of 205-225 BPM for periods of 35 to 40 minutes during the workouts.

Your heart has no idea what you’re using your muscles for, whether it is running, cycling, swimming, strength training, etc. If the muscles are working harder, the cardiovascular system must also work harder to supply the working muscles with oxygen and remove the metabolic-by products of intense muscular work. Some supposed “experts” claim that for an activity to qualify as “aerobic,” or to be effective for cardiovascular conditioning, it must involve continuous, or “steady-state” work of the muscles in the lower body, such as is the case in running or cycling. This simply is not true.
I can understand how they would come to this conclusion though. Since most
people have much more muscle mass in their legs than in any other part of the
body, it is easy to achieve a significant degree of HR elevation by performing
only moderate intensity activity using those muscles. Most upper body exercises, however, do not involve enough muscle mass to place a significant demand on the cardiovascular system if only performed with a moderate degree of intensity.

Realize that the majority of these so-called “experts” have never properly performed a single set of a high intensity exercise in their lives, much less an entire high intensity
workout. And, if they strength train at all, they do so using such fast movements that meaningful muscular loading is almost entirely non-existent, and probably rest so long between exercises that any degree of HR elevation achieved quickly subsides. These people have no experience with high intensity training, absolutely no idea what truly intense muscular work is, and absolutely no idea what kind of demand proper exercise places on the cardiovascular system.

It is not uncommon for endurance athletes, who typically consider themselves to be in superior cardiovascular condition and who have performed what they believed to be proper strength training in the past, to comment on how much of a demand  high intensity strength training places on their cardiovascular system. Even marathon runners and triathletes, athletes that many consider to be the picture of cardiovascular fitness, have asked to be allowed to pause and rest in the middle of their workouts, claiming they needed to “catch their breath.”

As long as one is working some significant part of their body at a high degree of intensity, there will be a demand on the cardiovascular system, and as long as one does not allow a significant degree of rest between exercises, the HR will remain elevated for
the duration of the workout. Properly performed, strength training does everything aerobics is supposed to do, more safely, more efficiently, and more effectively. Why destroy your musculoskeletal system for the sake of your cardiovascular system doing aerobics, when you can improve both with properly performed high intensity strength training?

Arthur Jones once said: “rather than be remembered as the man who saved America’s
hearts, Cooper [Kenneth Cooper, MD, the "Father of Aerobics"] will more likely be remembered as the man who ruined America’s knees.”

A large percentage of the improvements in physical or athletic performance and physiological changes such as a decrease in resting heart rate (RHR) that many people assume to be caused by improvements in cardiovascular efficiency, are actually due to increases in muscular strength and endurance and improvements in metabolic conditioning.

Realize that there is no correlation between resting heart rate (RHR) and physical fitness. RHR alone is not an indication of one’s level of physical fitness. It is simply a clinical measurement, and must be considered within the context of various other
factors. While a RHR in the low 40′s is often considered to be a sign of superior physical condition, within the context of other symptoms such as sweating, chills, abnormally low body temperature and a pale complexion it would be an indication of a serious medical emergency. However, a change in one’s average RHR may be an indication of an improvement or decrease in one’s level of fitness. A decrease in one’s RHR is usually attributed to an improvement in cardiovascular fitness, and is assumed to be an indication of an increase in stroke volume and ejection fraction. However, a decrease in RHR is more likely the result of an improvement in metabolic conditioning. It is so much a matter of an increase in cardiac output as it is an improvement in the muscles’ ability to utilize what’s being sent to them, which decreases the demand placed on the heart, both at rest and during intense physical activity.
Not to mention the degree to which cardiac output can be increased is very limited, and very quickly achieved by proper training. Past a certain point, increases in the size of myocardia would begin to actually decrease the volume of the left ventricle and obstruct outflow through the aorta, which would decrease cardiac output. This is common in athletes who abuse cocaine.

Improvements in metabolic condition probably contribute much more to decreases in RHR and in HR elevation during intense physical activity than increases in cardiac output. Such metabolic conditioning can be achieved through proper strength training. It’s the muscles ability to use what’s being sent to them, more than the heart’s ability to send it that’s important.

What amazes me is that despite the fact that the Surgeon General has basically stated that any activity slightly more demanding than watching TV when performed regularly will help improve and maintain cardiovascular fitness, there are people who will say that high intensity strength training, which is the most brutally demanding form of
physical activity ever devised, will do nothing for the heart. That this is nonsense should go without saying. And, if all that is necessary for cardiovascular fitness is going for a short walk or working in the yard, or performing some other light activity for a few minutes every day, then why do hundreds of thousands of people insist on destroying their joints and spines by jogging?
Because they believe it will help them lose fat? More nonsense.

Aerobics does not burn enough calories to be worth performing for that purpose. If a person does something for the sole purpose of burning calories, their time is not worth much. A 150-pound man running at a 7mph pace will burn, at most, about 8 kcals per
minute, or 480 calories per hour. He would probably burn about 100 of those kcals if he sat and did nothing for an hour, so the actual extra kcals expended as a result of the activity would amount to only 400 or so. If he did this every night for a week, he wouldn’t burn enough calories to equal the amount stored in one pound of fat. Such a high volume and frequency of running probably would cause a significant loss of muscle though. Since a muscle yields only 600 kcals, compared to the 3,500 kcals in a pound of fat, it would be possible to lose over 4 pounds of week in such a manner if one was losing muscle weight. Note that most habitual joggers, marathon and ultra-distance
runners, and other obsessive/compulsive aerobics addicts often have the sickly skeletal appearance of Nazi death-camp refugees and AIDS victims. This is hardly a healthy appearance.

The only effective way to create a negative net-calorie balance is to follow a reduced calorie diet. It’s much easier and far more time efficient to simply eat less, than to spend hours a day, several days a week pounding your joints on the pavement or slaving away
on some oversized hamster-wheel. And when you’re not wasting hours a week on
the stepper or treadmill, you’re going to get much better results from your strength training. If one truly desires to increase their caloric expenditure, then it is strength training they should focus on.

Aerobics only burns calories while you’re doing it, and damn few at that. Some people will point out that the metabolism is also elevated for several hours afterwards, but this increase is negligible, and hardly worth it. Aerobics can cause you to burn fewer calories
the rest of the time though, since when taken too far it can cause a loss of muscle, and can prevent your body from producing the increases in muscular strength and size stimulated during strength training.

Strength training, on the other hand, increases the amount of calories your body burns all the time, 24 hours a day, 7 days a week. Research from Tufts has indicated that every pound of muscle added to the body of an adult human increases caloric expenditure by an average of 50 calories per day. If one gains 5 pounds of muscle, which most  previously untrained subjects can achieve in a matter of weeks, one’s average daily caloric expenditure is increased by 250, for an increase in weekly caloric expenditure of 1750, the amount of calories in half a pound of body fat.

More importantly though, is that proper strength training is absolutely necessary to ensure discriminate weight loss while dieting. If one diets, or does aerobics, or both, but does no strength training, the weight lost will come from a combination of fat, muscle,
and organ tissue. Muscle is a very highly metabolically active tissue, and when your body perceives a reduction in caloric intake, it’s going to try to adapt by reducing its caloric expenditure. One of the most effective means of accomplishing this is to decrease the amount of metabolically expensive tissue, one of the most expensive being muscle. Strength training is necessary to ensure that the body maintains, and hopefully increases muscle mass while fat is lost.

And no, combining aerobics and strength training won’t produce better results. Adding aerobics will make things worse. It will prevent much of the improvements stimulated by the strength training workouts, and keep you chronically fatigued and hungry.
Research by Westcott and Darden have demonstrated that strength training and diet produce greater improvements in body composition when not performed in conjunction with aerobics.