well, circuit training alone is designed to incorporate either endurance or stamina training, or a compbination of the two. what determines whether or not its focus will be endurance or stamina is mainly the amount of weight (load). the lighter the load and higher the reps to failure/fatigue, the more predominate the red slow twitch fibers will be during the training session. here's a post that i commented on with a breakdown of the various muscle fiber types and their composition http://www.eroids.com/forum/training-nutrition-diet/workout-exercise/lit....

in this training approach, you'll be focusing primarily on the red fast twitch fibers. as a result, your metabolism will be closer to the anaerobic/aerobic threshold. you can still notice some increases in size and strength, as well as reduction in body fat due to the increased heartrate. this will mostly be stamina focused. killer workout btw