Circuit training is without a doubt one of the most effective/efficient forms of training! Circuit training involves taking a group of exercises and performing them one after the other with little to no rest.
Circuit training greatly increases conditioning, cardiovascular health, muscular endurance, strength, and it's amazing for fat loss! Due to the high amount of stress that circuit training places on the body it's best to use lighter weights, body weight movements, and less complex movements in order to reduce the risk of injury and maximize results.
If you're looking to dramatically increase you energy, drop body fat, improve your conditioning, and produce a lean/functional physique than circuit training is your answer! It's also great for producing amazing results in half the time most people spend in the gym. You can get an amazing workout in as little as 25-45 mins depending on your fitness level.
If you're a trainer who offers small group training, then circuit training should be something you're implementing in order to maximize not only income, but results and safety as well! By setting up a circuit that your clients cycle through, you'll be able to watch each of them and correct form with ease. Due to the nature of circuit training, you really don't need a large array of fitness equipment to get a great workout, saving you money on purchasing new equipment. I've even outlined great examples of body weight only circuits for fat loss and conditioning in my ebook "The Body Weight Solution".
So no matter who you are, what your fitness level might be, or what equipment you have access to, if you want to be in the best shape possible then you need to add circuit training to your fitness routine!