The Science of Circuit Training
So, what do we know about the science of circuit training? As I mentioned circuit training is as old as I am! Research studies on circuit training go back to the 1970s. Several studies at that time and since have shown improvements in muscular strength and endurance and aerobic fitness following circuit training. In fact, a leading researcher during this early phase of research concluded that “programs of running combined with circuit weight training or circuit weight training alone are very effective and equal in the improvements observed for aerobic fitness, strength and body composition.”
However, not all studies show such improvements. Why not? It could be due to the research subjects or many of the variables that go into program design, like frequency, intensity, recovery, number of exercises, or duration of the training session or duration of the study.
Another potential reason for the null results could also be due to something called the “The Interference Effect”. The interference effect does just want it says–it interferes or alters the physiological adaptations that normally occur as a result of specific endurance training or specific strength training when there is concurrent training of both endurance and strength. The muscles are basically being subjected to different physiological demands at the same time. Maybe it’s a 30-minute cardio bout on the exercise bike followed by a 45-minute heavy strength training session. When this type of training occurs, some studies show that the gains in muscle strength, power and hypertrophy are lessened compared to if the subjects were only doing strength training.
Another consideration is improving aerobic fitness in already highly aerobically fit individuals. One study showed that resistance circuit training may not be sufficient to improve aerobic fitness in this group.
One group that certainly sees benefits in resistance circuit training are the untrained. Obviously, any significant amount of physical activity will improve the health and fitness of this group, but again with circuit training both aerobic fitness and muscular fitness can be improved within a single training session. And, for many of these individuals “not enough time” may have been a primary excuse for not exercising.