In the past I’ve described a number of studies that have examined which type of aerobic training is best for losing bodyfat’and each study appears to contradict the one preceding it. One shows that interval training, characterized by alternate periods of high and low intensity based on heart rate, works best, while the next shows that low-intensity, continuous aerobics is better.
Here we go again: A study published in 2001 compared interval, or discontinuous, training with continuous aerobic exercise to see which resulted in the greater loss of bodyfat.1 Fourteen untrained male volunteers were divided into two groups that trained three days a week for 10 weeks on either an interval or continuous aerobics program. The interval group did 25 bouts per session of low-intensity aerobics for 80 seconds alternated with higher-intensity periods of 40 seconds. The continuous group exercised for 50 minutes at a moderate intensity level’50 percent of maximal oxygen intake.
Higher-intensity exercise produces a greater release of epinephrine, which promotes lipolysis, or fat breakdown, during exercise. So you’d expect higher exercise intensity to result in a greater fat loss. The problem is that higher-intensity exercise leads to lower levels of fat in the blood for various reasons, including increased lactate levels, which turn off fat release. The idea behind interval aerobics is that by dropping to a lower intensities, you open the gates of fat-cell release. By alternating higher and lower intensity, you deplete energy substrates to the point where your body is forced to use additional fat following the exercise. Add it all up, and interval training should promote the greater fat loss.
In this study, however, neither mode of exercise proved superior for fat loss; the authors think the two exercise formats were too similar in intensity. Because the subjects were untrained men, both exercises were designed to make it easier for them to complete the workouts, which led to their requiring similar intensity levels despite the intensity spikes in the interval group.
The use of untrained subjects was a major flaw of the study. They were not merely untrained’they hadn’t exercised at all prior to the study. Nevertheless, most other studies show that beginners are better off using low-intensity aerobics to condition their cardiovascular system and build up the oxidative enzymes muscles need for efficient fat oxidation during exercise. Actually proving whether interval or continuous aerobic training is superior for fat loss would require using more experienced trainees, evenly matched in body composition and fitness levels, as subjects.
1 Mader, U., et al. (2001). Influence of continuous and discontinuous training protocols on subcutaneous adipose tissue and plasma substrates. Int J Sports Med. 22:344-349.