Thumper:
This is a machine that delivers a percussive massage. Almost all automatic massage devices deliver their forces “horizontally”, effectively, taking your skin, and moving it above the deeper tissue. The thumper applies its forces “vertically”, effectively playing a drum roll on your skin, massaging the deeper tissue and musculature. This is generally used to quickly loosen up the musculature before or after an adjustment, or to quickly loosen up severe knots before starting massage by hand.
Possible side-effects include soreness, and minor bruising.