Originally Posted by
OBoile
Might be best to refrain from using that term unless you're discussing artwork then.
This is false. Aerobic exercise does not significantly increase the amount of lean muscle mass, nor does it signal the body to build/retain muscle to any significant degree.
Also, burning fat and increasing the amount of muscle are two distinct processes. One does not happen as a result of the other.
Also, muscle "density" isn't really a thing. Muscles can grow or shrink. Certain other adaptations within the muscles can occur, some of which are caused by aerobic activity, but that doesn't make them significantly more dense.
Finally, you are constantly burning fat reserves. Constantly. The consumption of fewer calories than what you expend is what causes fat loss. Aerobic exercise will increase caloric expenditure, but it isn't necessary for fat loss. So the "sufficient quantity" is 0.
Strength training. Lifting heavy things, or pushing against a sufficiently difficult resistance. This causes a different adaptation within the body than producing a low amount of force for an extended period of time, as is the case with aerobic exercise. Specifically it sends a strong signal to the body to build/retain as muscle. One look at the bodies of elite strength athletes vs elite endurance athletes should make this quite clear.
Sculpting is a metaphor. If you don't understand metaphors, I can't do anything about that.
As for fat burning occurring "constantly," this is a denial of the nature of fat within the body. Fat is a reserve energy resource that doubles as a reserve water "sponge" (another metaphor).
Constant fat burning ONLY occurs in people experiencing a calorie intake deficit in comparison to the caloric expenditure of energy and body maintenance functions, plus any exercise induced calorie consumption added on top of that by either aerobic or anaerobic workouts.
People who are generally overweight and out of shape may not burn any fat at all as part of their normal metabolism. That is why they have such trouble losing weight. As long as calories in exceeds or equals calories out, the fat burning engine has no need to turn on and the body preserves the fat. The body then stores any newly eaten fat, and converts proteins eaten in excess of need to additional fat. This process arose over the eons as evolving Nature decided what processes worked best for living organisms. The process is known as "homeostasis."
Eating a lot of carbs or drinking alcohol can easily tip the scales from burn to save mode, as alcohol adds calories at the rate of 9 per gram, twice that of carbs, with zero nutritional benefits.
As for an AirDyne not providing a resistance workout, physics is physics whether you are pushing air or iron around. Over the course of one year, I went from 185 lbs. to 211 lbs., while losing two inches from my waist and adding three inches to my chest, four inches to my biceps and three inches to my thighs. During that same period of time, I spent no energy pumping iron, or sitting in a Universal Weight Machine seat.
Muscle is added when the body sees a need and sufficient protein is available in the diet to allow it. It's that simple.