I am an avid CrossFit athlete and one of our major activities is Kettlebell swings. Normally I am partial to a Russia KB swing, however more recently I have been experimenting with the American style. Is there any difference in form or muscle emphasis in these movements?
The Russian kettlebell swing is direct out and away from you, then you let it fall down and go between the legs again for another rep. The American swing continues on and is raised up above the head, involving the shoulders, whereas with the Russian swings the shoulders are not used to move the weight at all.
So, a quick difference is that the American swing adds more emphasis on the shoulders.
There are several ways to perform the American swing though. In recent years the CF community has changed the American swing to become more efficient and turn into more of a double arm snatch rather than a swing and shoulder raise.
This video shows a good comparison.
Strictly speaking, there is no inherent difference between the two techniques: given enough momentum, the kettlebell will continue in an arc to, and beyond, the overhead position. In practice, however, athletes might tend to engage the shoulder flexors (anterior deltoid, biceps brachii, and clavicular pectoralis major) more with the American swing, due to limitations in the amount of power that they can deliver from the legs, and their ability to adjust their posture to control the centripetal force. This would be particularly true when the mass of the kettlebell is proportionally high relative to the mass of the lifter.
The technical challenges associated with the 180° swing would likely encourage a two-phase lift, in which the legs and hip provide the primary starting power, and the shoulders take over towards the end of the swing to deliver the kettlebell to the overhead position. Of course, there is always scope for significant variation in the performance of any technique. In this case, the force for the movement could theoretically come entirely from the legs and hip, or almost entirely from the shoulders, with the posterior chain acting primarily as a synergist. This distinction is demonstrated well by the two lifters in the video (which was posted, also, by another contributor). The variations demonstrated really represent two functionally distinct exercises.
The key issue I have with the American technique is why? Since the kettlebell finishes overhead, its weight at the point of zero velocity is straight down. This is generally undesirable with a kettlebell (as opposed to, for example, a dumbbell) of any substantial weight because the load is difficult, even hazardous, to control with the relatively weak wrist flexors and extensors. The inherent function of a kettlebell is to provide a dynamic load suitable for swinging. If the point is to muscle the weight up using the shoulders, a dumbbell, barbell, cable, or some other apparatus would likely be more appropriate.