Kettlebells deliver xtreme all around fitness.
Voropayev (1983) observed two groups of subjects over a period of a few years and tested them with a standard battery of armed forces PT tests: pullups, a standing broad jump, a 100m sprint, and a 1k run. The control group followed a typical university physical education program that emphasized the above. The experimental group just lifted kettlebells. In spite of the lack of practice on the tested exercises, the kettlebell group showed better scores in every one of them!
Researchers at the Lesgaft Physical Culture Institute in Leningrad (Vinogradov & Lukyanov, 1986) found a very high correlation between the results posted in a kettlebell lifting competition and a great range of dissimilar tests: strength, measured with the three powerlifts and grip strength; strength endurance, measured with pullups and parallel bar dips; general endurance, determined by a 1000 meter run; and work capacity and balance, measured with special tests!
Shevtsova (1993) discovered that kettlebell training lowers the heart rate and the blood pressure. « Gomonov (1998) concluded that "Exercises with kettlebells enable one to quickly build strength, endurance, achieve a balanced development of all muscle groups, fix particular deficiencies of build, and they also promote health." Most methods that claim 'all around fitness' deliver no more than compromises. Accept no compromises!