Some people will get SS's, tri sets, giant sets, ect confused with circuit training. There are many versions of circuit training and some newer gyms trends, designed for women (Curves, etc), will only give classes using machines rather than free weights. Basic concept is going from one exercise to another without any rest at all with a set amount of exercises.This can be from 3 to 8 exercises or more. After the last exercise is done than you return to doing the first exercise again (no rest) and start all over again.You can also call this loop training. Usually the exercise picked are differnt body part, going from one to the other. Legs,BP,abs,lats,calves,delts,biceps is an example.Doing five to 10 cycles in all. You want to keep the blood moving from one body part to another, usually a opposite muscle group. That was, as far as I know, the original concept. The PHA system is a prime example and can be very effective in giving outstanding stamina (endurence & strength). I've used the PHA (Perpetual Heat Action) getting ready for football season with great resutls. Athletics do different versions of Circuit train in their preformance training. You can hold the muscle size, increase strength somewhat and lose body fat fairly fast.
Many take the PHA system (or other forms of Circuit training) beyond the one unit of 5 to 10 exercises. Adding two or more units in a single workout are really normal workouts. Some athletics I know say that they can take marathorn runners and have them gasping for breath after 10-15 minutes or so on the PHA ( or workouts like it) system. That's there story anyway, but because marathorn runners do not train with weight bearing (the time under stress), different exercises and have a very short range of leg extensions/push off (short running steps) there may be some truth to this. PHA will call into action both the red and white fiber of a muscle. An oxygen debt ,in a somewhat short period of time, can occur if not familar with this type of training. Good Luck.
