The principle of specificity of exercise states that exercise must be specific for a certain purpose. In simple terms, if you want to build muscle and get stronger, you use a progressive resistance style of training, with the most efficient being weight training.If cardiovascular conditioning or increased endurance is the goal, then aerobic or endurance exercise is best. For flexibility, various stretching movements are in order. There is some overlap with these various forms of exercise. For example, when engaged in weight training, you can begin every repetition with a pre-stretch, which involves an extended range of movement at the start of the movement. When you do this, you line up muscle fibers in such a way that the result is stronger muscle contraction. Training in this manner also boosts levels of intramuscular insulin-like growth factor-1 (IGF-1), a major anabolic hormone produced in the muscle. But just the fact that you are including a stretching motion in concert with lifting a weight provides a stretching component that does boost muscle flexibility. In effect, you are doing two types of exercise simultaneously. Indeed, recent research shows that using this inter-exercise type of stretching not only provides the necessary flexibility component of fitness but also is superior to doing a separate stretching session prior to a weight workout. Doing that reduces muscle strength by as much as 23%, and relates to the importance of tighter connective tissue contributing to a more potent muscular contraction during an exercise.
What about combining both endurance and strength components in one workout? This doesn't refer to concurrent training, where an aerobic session is done either before or after a workout (that was covered in a recent issue of Applied Metabolics), but rather lifting weights in a style that would work both the muscles and the cardiovascular system simultaneously. The style of training used for this purpose is known as circuit training. Circuit training involves doing a series of weight exercises with no pause between exercises. Other than the lack of rest between exercises, training is done in the normal style. Another term for this type of training is giant sets, a reference to the fact that you are doing several exercises, but counting them as one set. The question is: How efficient is this combination training for both developing cardiovascular fitness, as well as helping to oxidize or "burn" excess body fat? Aerobic exercise is considered superior for purposes of increased fat oxidation because it involves a higher intake of oxygen. Since fat can only be efficiently oxidized in the presence of oxygen, it's obvious that the type of exercise with the highest use of oxygen would be the best "fat-burning" exercise. While aerobics . . .