What is kettlebell training?

In one line

Kettlebell training is strength training done by lifting or swinging a kettlebell, a round iron weight with a handle.

What is kettlebell training?
The exercise where you swing an iron weight with a handle
In a corner of the gym, round iron weights with handles sit in rows by size. You often see people grab one with both hands and swing it forward from between their legs. This post explains what a kettlebell is and which muscles kettlebell exercises use.
In a nutshell
Training with an iron weight that has a handle
A kettlebell is a piece of exercise equipment: a round iron weight with a handle on top. Its shape is often compared to a cannonball with a handle. Kettlebell training is strength training done by lifting or swinging it.
Where it came from
A weight once used for weighing in Russia
In Russia, kettlebells were used from the 1700s as weights for measuring the weight of goods. In Russian they are called 'girya'. In Russia they became a symbol of strength, used everywhere from circus strongmen to army training.
The signature move: the swing
Swing it forward from between your legs
The signature kettlebell exercise is the 'swing'. You hold the kettlebell with both hands, lower it between your legs, then swing it forward and up using the force of straightening your hip joints (where the legs attach to the trunk). Swinging to chest height is called a 'Russian swing'; swinging overhead is an 'American swing'.
Folding, not sitting
The 'hip hinge': folding and opening at the hips
In the Russian swing, which goes to chest height, on the way down you bend your knees only a little, push your hips back and lean your upper body forward. Folding and opening at the hip joint like a door hinge is called a 'hip hinge'. The deadlift, where you lift a barbell off the floor and stand up, uses the same movement.
Muscles the swing uses
Buttocks, back of the thigh, lower back
Measured with EMG (a recording of the weak electrical signal muscles give off when they work), the swing made the gluteus maximus (buttock muscle) and the hamstrings (back-of-thigh muscles) work hard. The erector spinae, the muscles running along the spine at the lower back, also worked.
Beyond the swing
There is even a lifting competition
People also do moves like a squat holding the kettlebell in front of the chest, and the 'snatch', lifting it overhead with one hand in one motion. There is also a competition called 'kettlebell sport', where people compete at lifting kettlebells overhead within a set time.
Effects studies found
Leg strength and jumping improved
In a study where people did kettlebell swing training for 6 weeks, maximum leg strength and standing jump height increased. But in a study comparing it with barbell weightlifting and squat training, maximum strength rose more with the barbell. A review gathering kettlebell studies also found the effects were mostly small.
A common misconception
Is the swing an arm lift?
No. The power of the swing comes mainly from straightening the hip joints. In a study comparing people used to the swing with people just learning it, those used to it moved their hips first on the way up, with the shoulders following. In those just learning, this order was reversed, and they raised their arms higher.
Summary
Swing an iron weight with a handle using hip power
Kettlebell training is strength training done by lifting or swinging a round iron weight with a handle. The signature move, the swing, is driven mainly by straightening the hip joints rather than by the arms, and it works the buttock and back-of-thigh muscles hard. Related terms: deadlift, gluteus maximus, hamstrings.