Those cast-iron or steel balls which look like small cannonballs with a thick metal looped handle on top can be useful for working on joint flexibility as well as functional-type movements (e.g., deadlifts).  One of the key benefits of working with kettlebells is the possibility to work the entire body for a powerful and efficient workout.  Other benefits include increasing strength (including core strength), power, endurance, flexibility, mobility and cardiovascular capacity.  You can achieve a strenuous workout in less than thirty minutes.  
     Standard kettlebell exercises should incorporate four basic movements:  the press, the pull, the squat, and the deadlift.  Examples include shoulder press, bent-over row, sumo squat, and Romanian deadlift.  Swinging the kettlebell (e.g., single- or double-arm swings) is another example of a pulling movement that makes the kettlebell uniquely beneficial for training purposes.  The end result is the incorporation of more muscle groups, including your core muscles (i.e., abs, lower back, glutes, and hamstrings), being worked.  Studies have shown that using kettlebells can improve coordination and balance in addition to increased muscle strength and endurance.  By swinging one or two kettlebells, you will be able to target your hips, back, glutes, shoulders, and legs.  An additional benefit is increasing grip strength.
     If you minimize the rest periods between sets, you can also get a cardiovascular workout with kettlebells.  Be sure to start out with lighter weights in order to get a feel for the movements and an understanding of how to properly control the weights.  The risk of injury (i.e., torn muscle, tendon, ligament) increases greatly if the kettlebells are too heavy, are swung incorrectly (i.e., away from the sagittal plane) or are swung too strenuously.  Focus on using good form by improving your technique.  Sloppiness is a recipe for injury.  
     The benefits of kettlebell training include:
  • Efficient, quick workout incorporating many fitness components (i.e., strength, endurance, power, flexibility, cardiovascular)
  • Requires minimal space
  • Relatively inexpensive
  • Excellent way to condition your body for sports due to functional movements
  • Ideal tool for gaining core strength
     The drawbacks of kettlebell training include:
  • Limited weight capacity
  • Fixed weights

Bottom line:  Kettlebells can be useful for anybody but should be utilized as a complement to your workout program rather than your exclusive workout program.  Kettlebells should be thought of as a tool in conjunction with dumbbells, barbells, machines, and cables as another means to enable yourself to gain strength, balance, coordination, endurance, and good cardiovascular conditioning.