I don't train with anything other than kettlebells and I get this question a lot: how are kettlebells different to dumbbells? And this is usually followed by: are kettlebells better than dumbbells?
I'll start by answering the second question:
Are Kettlebells Better Than Dumbbells?
There are many, many fitness tools out there, some more effective than others and most have their place (except perhaps the Ab-Doer). The question "are kettlebells better than dumbbells?" is best answered with a question: "what do you want to get out of your training?"
If the answer is hypertrophy, then you're better off sticking with the dumbbells (although hypertrophy can be achieved with kettlebells, dumbbells are more suited for it).
If the answer is all round fitness, weight loss, enhanced sports performance, mobility, strength endurance, power endurance, cardiovasular fitness, improved posture or coordination then kettlebells are the superior tool. There's a good reason kettlebells are the tool of choice for GPP (General Physical Preparedness) in the Russian military!
This then brings me back to the first question, as the differences between the two explains why kettlebells usually come out on top:
How Are Kettlebells Different From Dumbbells?
The kettlebell has a displaced centre of mass – that is the centre of mass sits away from the handle rather than the weight being evenly evenly dispersed on either side of the handle.
The displaced centre of mass, and the kettlebell’s unique shape, set it apart from dumbbells for the following reasons:
Functionality - The displaced centre of mass makes the kettlebell behave more like the objects we come into contact with in everyday life, therefore kettlebell training has much better transference to everyday functionality and to sport than dumbbell training.
Joint Health & Stability - The displaced centre of mass makes the kettlebell more unwieldy than a dumbbell, therefore the body has to work harder to control it. This means that the kettlebell is better at switching on core and other stabilising muscles and key postural muscles.
Energy Use - because the kettlebell generally turns on more muscles than a dumbbell, the kettlebell works the body harder, greater calorie burn for the same amount of time spent training.
Ballistics -The displaced centre of mass and unique shape make the kettlebell ideal for ballistic lifts such as swings, cleans and snatches. The ballistic lifts are great for power generation, for targeting the all important posterior chain of muscles (hamstrings, glutes, lower back and upper back) and simultaneously getting a cardio and resistance workout. The posterior chain activation is great for postural health and it is the posterior chain that drives most movements in sports, such as running, kicking, striking and jumping, so kettlebell ballistics are great for sports performance.
Variety - The unique shape of the kettlebell means it can be held in a number of different ways: bottoms up (so that the body of the bell is above the handle) or it can be held so that the body of the bell sits on the hand. The kettlebell can also be passed easily from hand to hand and even juggled, making it much more versatile (and more fun) than a dumbbell. Incidentally, kettlebell juggling is a very good way to build super-strong connective tissue.