Most studies that have examined what happens when you combine aerobics and weight training show that it defeats the purpose of lifting. Doing aerobics promotes changes that increase oxygen use and the use of fat as fuel. Weight training promotes increased muscle protein synthesis. Doing aerobics ups the body’s production of such substances as AMPK, which leads to greater fat use at the expense of muscle protein synthesis.
Does that mean aerobics is taboo for anyone interested in building muscle? No: There are simple ways to overcome the incompatibility. Do your aerobics at a different time—or on a different day.
The most effective approach is to use interval training, a type of aerobics that includes some anaerobic work. You alternate moderate and high levels of intensity in one training session. The net effect is that you can get all of the considerable cardiovascular benefits of traditional steady-state aerobic training with increased fat oxidation—and in less training time than with traditional aerobics.
The effectiveness of interval aerobic training is evident in the results of a recently published study that featured eight women, including moderately fit women, sedentary women who did no exercise and an active soccer player. All in their 20s, they trained every other day for two weeks, using a high-intensity interval workout done on stationary bikes: 10 sets of four-minute high-intensity bursts, using a level of intensity equal to 90 percent of their maximum oxygen intake, alternated with two-minute rest intervals between sets, in which they cycled at low intensity.
The starting point of fitness made no difference in the results. The women showed an average increase of 36 percent more fat burned at the end of the study. Their cardiovascular fitness also rose by an impressive 13 percent.
How to explain such rapid results? It turns out that interval training is particularly effective at boosting activity in the portion of cells where fat is burned and oxygen is used, the mitochondria. The study authors noted that the women showed signs of increased mitochondrial volume, as evidenced by a rise in enzymes associated with fat oxidation and oxygen use.
The training also increased the activity of a protein that transports fatty acids into the cell, where the fat is oxidized. Even more impressive was that there was no significant loss of muscle glycogen, pointing to an almost exclusive use of fat as fuel during the exercise. The fat used during the exercise was likely derived from free fatty acids circulating in the blood, since levels of fat stored in muscle didn’t change. The authors suggest, however, that tapping into intramuscular fat may involve long-term adaptations that didn’t occur in the short-term study.
Other studies of interval training have found an increase in enzymes required for fat oxidation of 10 to 35 percent after only two weeks. Studies that have compared interval to conventional long, slow moderate-intensity aerobics show interval training produces similar beneficial effects but with 90 percent less training volume. One study showed similar improvements with 2.5 hours a week of interval work compared with 10.5 hours a week of conventional aerobics.
Unlike conventional aerobics, which increases resting metabolic rate only during actual exercise, interval training leads to a sustained rise in resting metabolic rate. That means you wind up burning more calories at rest, typically calories derived from fat stores. The only other type of exercise known to do that is weight training. The fact that weight training works mainly type 2, or fast-twitch, muscle fibers explains the rise in metabolism, since the repair of damaged fibers induced by weight training leads to biochemical changes that result in a higher resting metabolic rate. Intervals also tap into type 2 fibers during the high-intensity phase, explaining why that style of aerobics—unlike traditional aerobics—also results in a more sustained rise in resting metabolic rate. The slow phase of intervals shifts the focus to type 1, or slow-twitch, muscle fibers, which preferentially burn more fat than type 2 fibers.
Add it all up, and it’s evident that interval training is ideal for bodybuilders. You get all the fat-burning and cardiovascular benefits associated with traditional steady-state aerobics without overtraining and muscle loss. Perhaps the best feature is that you get all the benefits in far less training time.
Want more evidence-based information on exercise science, nutrition and food supplements, fat-loss, ergogenic aids, and anti-aging research? Check out Applied Metabolics Newsletter at www.appliedmetabolics.com.
©,2012, Jerry Brainum.Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
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