"It don't mean a thing if you ain't got that swing"

The basic swinging movement from which torso (core) strength is developed and from which all other movements are based , requires the use of the physically large back and leg muscles. Each repetition requires activation of tonic (stabilising) muscles as well as phasic (moving) muscles. This contrasts with the situation with weight machines &  benches where part of the body is supported , assisting to negate the effects of gravity – less calories are burned , which is what your average gym owner maybe doesn’t want you to realise. That's why you have to stay there at least an hour!

Put simply , with kettlebells you have to work harder for each rep and indeed a kettlebell "rep" cannot be completed by cheating ; as each unit of “work” requires a corresponding expenditure of “calories” you become leaner more quickly . As you replace excess fat with lean muscle your metabolic rate increases so that even though your weight may remain the same , you utilise calories more efficiently.

Hence kettlebells , used in a free weight environment where the body must work against gravity , enable an highly efficient workout – much more can be achieved in a shorter time frame  as many muscles are activated.

The handle and off-centred weight translate to increased leverage and tremendous development of grip strength and grip endurance – useful in everyday life (luggage , undoing lids , removing champagne corks, undoing bolts & screws, carrying shopping , gardening and landscaping) and in numerous sports e.g. racquet sports, ball sports , rowing , martial arts. Swinging movements develop great muscle control – the muscles are taught to contract/relax appropriately , with a functional pattern and full , useful range of motion.

Strength + flexibility + endurance

Clearly , swinging and pushing weights improves strength. With kettlebells,  the emphasis is moving the joints in a natural & full range of motion , with equal emphasis of extensor & flexor muscles. When practised appropriately , muscle imbalances from side to side and from an extensor/flexor points of view are ironed out. Whilst using a weight machine however , the muscle may well be “isolated” (and is this really a good or beneficial thing?) , but in general the range of motion is greatly diminished. The aim with kettlebells is to develop muscles and joints which can act in the real world through the normal maximal range for the particular muscle/joint.

Though “free weights” are acknowledged as the most effective form of weight training , as a rule and as practised with dumbbells and barbells , these are flexor/extensor movements. All very 2-dimensional The spine and torso and limbs are however , designed to function in all planes of movement , including rotation. It is this rotational element which kettlebells work  Using kettlebells gives you the advantage of weight training (increased resilience through increased strength of muscles , tendons , ligaments, cartilage and bones) with the flexibility advantages of yoga (but without special emphasis on extreme flexibility , which can be detrimental to joints and to athletic performance).

As with yoga , most people find initially they are significantly tested with respect to flexibility and in particular stability/control at the edges of range of motion. Usually many joints are compromised  but with regular kettlebell  practise over a period of months to years , a full , normal , strong & controlled pattern can be regained.