I admit—when I first saw a trainer at my gym using a kettlebell with his clients several years ago I thought he was crazy. It looked as outdated as his clothes and seemed like something that time had forgotten. Well, fast forward to 2013, and I am now a huge advocate of kettlebell training. There is nothing more empowering than swinging around a heavy cast-iron ball. Not only do you gain enormous strength, but you get quite the cardiovascular workout from using them.

My gym is now well stocked with kettlebells and, as a result, I use them all the time—on my own, with clients and in my classes. Everyone is amazed on how effective they are, how strong they feel and how much of a workout they get from them as their heart rates go up on every swing and lift. Doing a circuit of kettlebell exercises is one of the toughest workouts they have ever had—and they all love it.

If you ever wondered what to do with those heavy, handled iron balls, here is a great kettlebell circuit that will surely leave you out of breath, but in great shape:

Two-arm swings: Grasp the kettlebell by its handle, get into a squat position and swing the kettlebell from between and behind your legs up to chest level. Be sure that your arms are straight, your back is flat, you bend your knees and that the power comes from the lower body. All the momentum comes from your lower body so do not think of it as a front raise. As you swing the kettlebell up, push your hips forward and lock your knees—and do not forget to squeeze those glutes as well. Let the kettlebell fall back down, but always keep it under your control.

Goblet squat and press: Hold the kettlebell in front of your chest with your hands on the outside of the handle rather than inside of it. Position your legs hip-width apart and lower into a deep squat. Your elbows should be lower than your knees or at least touching them. As you come up from the squat, press the kettlebell over your head.

One-arm swing: Similar to the two-arm swing, but now you will only be swinging with one arm. The same rules apply, however—straight arms, flat back, bent knees and momentum from the lower body. Do a set on one arm and then switch to the other.

Reverse lunge with a pass through: Put the kettlebell in your right hand and do a reverse lunge with your right leg. As you lunge back, pass the kettlebell under your left leg and into your left hand. Return your right leg back and then lunge back on the left leg while passing the kettlebell under your right leg to your right hand. Be sure your upper body is tall and not hunched over and your abs are tight.

Alternating one-arm swings: Here is one that will require some focus and coordination. Instead of performing all the swings on one arm at a time, you are going to alternate arms after each swing. As you swing the kettlebell up from a right-arm swing, grab it with your left arm and lower it back down. Now do a swing with your left arm and grab it with your right arm as you swing it to chest level. Keep alternating until you complete all of your reps.

Around the world: Here is one exercise for your core that you cannot do with regular weights. Grab the kettlebell with your right hand. Pass it in front of you to your left hand with your arms fairly straight and then take it behind and around your body passing it back into the right hand. You are swinging it completely around your body. The hand off will be both in front of your body and in the back. Keep your torso tight and straight without hunching or leaning back. Continue in one direction for your desired reps and then reverse the direction for the same amount of reps.

One-legged deadlifts: Hold the kettlebell in your right hand and lift your left leg off the floor. Keep a slight bend in your right leg and lower the kettlebell towards your right foot going as low as you can. At the same time, make sure your left leg is also going up as you lower your torso down so your body should be in one straight line where everything moves at once. Return to your starting position and then continue. Switch to the other side when you completed your set.

Sumo deadlift high-pulls: Stand with your legs further than hip width and hold the kettlebell with both hands down in front of you. Lower the kettlebell to the floor while doing a sumo squat with your butt back, weight in your heels and abs braced. As you come back up, perform an upright row with the kettlebell. The movement should be explosive yet fluid. Continue squatting and rowing making sure your back is flat when you lower the kettlebell and that your elbows are even with your shoulders (and not shrugging) on the row.

If you do this workout circuit-style—performing 15-20 reps for each exercise or doing them each for a set amount of time—you will definitely feel yourself getting stronger. You will also realize there is no need for any cardiovascular work once you are done. This workout takes care of that as well. There are many other great kettlebell exercises like Turkish get-ups, halos and windmills. You can incorporate these into your circuit as well or swap out some of the others for these. No matter which exercises you choose, the kettlebell will not disappoint!