If you have ever worked out with kettlebells, you know that a kettlebell workout differs significantly from free weight or dumbbell exercises.  Although kettlebells may be equivalent in weight to dumbbells, they engage different muscles because the center of gravity in a kettlebell exists on a vertical rather than a horizontal plane.

When, for example you initially grip a kettlebell placed on the floor, you hold it by a handle.   As you  begin lifting the kettlebell, you are engaged in a pulling motion.  As you raise the kettlebell, its center of gravity relative to your body begins to shift and at approximately shoulder height, the pull on your bicep, tricep and shoulder muscles becomes a pushing motion.

The effect of this change in the center of gravity in this sample exercise is to engage stabilizing muscles at multiple points in and around your arm and core.  By contrast, a standard biceps curl engages only those stabilizing muscles necessary to support your arm in a single plane of motion.

While kettlebells offer advantages over dumbbells, both are far superior to using exercise machines commonly found in exercise gyms.  This past Thursday, my regular workout partner, Michael, and I conducted an experiment to examine this difference.  The exercise we selected was an overhead triceps curl.  Our regular triceps exercise involves lying on an exercise ball with arms extended overhead, grabbing a 70lb. weight and raising 45 degrees until the weight is directly overhead.  My maximum for this exercise is currently 70 lbs. and Michael's is 75.

We decided to test our capacity on a pulldown machine, which triggers approximately the same muscles.  Each of us was able to comfortably pull down close to 150 lbs.  The reason - the pulldown machine does not engage any stabilizing muscles and requires movement in only one plane.  All muscle energy can be focused on one controlled movement.  This machine might be helpful building bulk, but I suspect that it would not be helpful creating strength.

Our next step is to substitute a kettlebell for the dumbbell in our exercise ball routine.  I would imagine that the center of gravity weight shift will occur at about a 20 degrees angle of lift.