What is wrong with Aerobic training depends on the rationale of its use. In terms of training for endurance activities it is part of sound training. But those people in the Physique world & General Fitness think they are employing aerobic activity for other reasons. If trainees think they are doing “aerobic training” to raise metabolism they are wrong. Not only does it not raise metabolism, it causes it to down regulate overtime. Look at the physiques of sprinters and gymnasts. Neither group does any sustained aerobic work. Why? Because it has huge costs to strength and power. Does their lean body mass suffer? No! It is enhanced by avoiding aerobic work and focusing on strength and power.
So all these Figure girls, bodybuilders, bikini girls and the general public doing all this aerobic volume are actually programming their bodies to not only use less fat, but to store it better. You become more “fuel efficient” by doing aerobic activity which means you burn less fat, not more fat.
The National Institute of Health did a study that uses a room calorimeter, that can measure oxygen uptake and respiration rates of people over a 24 hour period. When testing ultra marathon and tri-athletes performers, we’re talking about the best of the best, against average couch potatoes there was no difference in metabolism in a 24 hour period, when vital stats were controlled. In other words, even endurance athletes at the very high end of the scale, who do the most volume of work, do not get a metabolic pay off for doing so. Other than the calories burned during activity there is no up-regulation benefits of metabolism from aerobic activity, even over years!