That should depend on your client or patient you are working with. Everyone has the number “3” engrained as for how many sets. However, research has shown that 1 set verses 3 sets produced no significant benefit. (Chris Haus from UF). However, that does not mean I just perform one set of a particular exercise. Although it is good to keep in mind considering it is difficult enough getting clients to train, let alone for in a desired time frame.
The current ACSM Guideline for Muscular Strength and Endurance programming is 2-4 sets for each major muscle group.
Program your circuit class based on the type of participant, age, goals, etc. They is no one golden rule for circuit.
To slow down boredom, I do different formats.
*8-10 stations, 2 sets
*20 stations, 1 set.
*8-10 stations, 1 set followed by another type of 8-10 station, 1 set
With circuit training, I think it’s more important to look at overall volume and making sure that all muscle groups are worked equally.
I like many formats, but my personal favorite is to switch between 3 minutes of weight training (random exercises) and 3 minutes of cardiovascular conditioning. For example:
45 seconds Seated Row
45 seconds Leg Press
45 seconds Shoulder Press
45 seconds Abdominal crunches
45 seconds 5.0 mph (treadmill)
45 seconds 5.5 mph
45 seconds 6.0 mph
45 seconds 6.5 mph.
Works great for large classes without a lot of equipment. For personal training sessions, I’d replace the treadmill work with some calisthenics or metabolic conditioning where I can provide a bit more personal feedback to a client.