Circuit training is a high-intensity aerobic and anaerobic workout that involves circuiting through a series of different strength-training exercises with little or no rest in between sets. There are no rules on what exercises to include in the workout, making it an effective option for people exercising at home or in the gym, no matter their fitness level. Although, results will vary, you may begin to notice improvements in your aerobic endurance, muscular strength, energy levels and weight loss within a few weeks.
Improved aerobic endurance will be one of the first benefits your will notice from regular circuit training. Although, this is contingent upon the amount of time you exercise weekly and your current fitness level. A sedentary person just beginning circuit training that exercises three to four days a week at a moderate-intensity should begin to notice some initial improvement in aerobic endurance within one to three weeks, according to the American College of Sports Medicine.
Initial improvements in muscular strength should occur as early as two weeks after beginning a circuit training program. In order to continue to see improvements in muscular strength, it is necessary to change your routine as often as every four to six weeks, either by performing different exercises or increasing the load or number of repetitions and sets you are performing.
Energy levels should improve almost immediately after beginning a circuit training program. Exercise increases blood flow throughout the body. When this occurs you will first experience an immediate improvement in energy after you have exercised. Within one or two weeks of exercising three or four times a week, your body will start to adapt to the increased activity levels, and as a result, you will feel more energetic throughout the day, and may even notice improved sleep.
While fat loss is what many people want to notice first, it may take a three to four weeks before beginning to notice improvements primarily because a major part of fat loss has to do with diet. However, with regular aerobic and muscular strength training, you become much more efficient at using fat as an energy source for exercise, according to Jack H. Wilmore and David L. Costill, authors of "Physiology of Sport and Exercise."