A motorized machine for passively applying a tapping force to the bottoms of a user's feet, the machine comprising: a housing; an axis-defining mechanism coupled to the housing, the axis-defining mechanism configured to define a rocking axis; at least one pedal (10, 12) positioned to receive a foot of the user and mounted on the rocking axis for rocking movement of the at least one pedal; a motor arranged within the housing, the motor configured to generate rotational motion to an output shaft of the motor; a pedal rocking mechanism coupled to the output shaft and driven by the motor, the pedal rocking mechanism being configured to translate the rotational motion generated by the motor to reciprocating rocking up and down motion of the at least one pedal about the rocking axis; and at least one bumper, height-adjustably coupled to the housing, located under and apart from a bottom portion of the at least one pedal, the pedal rocking mechanism comprising a camshaft coupled to the output shaft of the motor, a cam eccentrically coupled to an end of the camshaft, and a pedal coupling member coupled to an underside of the pedal, the pedal coupling member including a channel, the cam being arranged in the channel to convert rotational motion of the cam to reciprocating motion of the pedal coupling member so as to provide a positive application of force for driving the bottom portion of the pedal up and down towards and away from the at least one bumper, wherein the motor, the pedal rocking mechanism, the at least one pedal (10, 12) and the at least one bumper are configured so as to cooperate to, during operation of the motor, cause the bottom portion of the at least one pedal to tap against the at least one bumper at a bottom of a downward stroke of the pedal so as to provide pulsatile acceleration to the bottom of the user's foot, wherein the height of the bumper is adjustable to allow for tapping that provides pulsatile acceleration of about 0.1 g to 0.5 g, thus being sufficient to increase pulsatile shear stress to the endothelium, of sufficient magnitude to cause the release of beneficial mediators. a housing; an axis-defining mechanism coupled to the housing, the axis-defining mechanism configured to define a rocking axis; at least one pedal (10, 12) positioned to receive a foot of the user and mounted on the rocking axis for rocking movement of the at least one pedal; a motor arranged within the housing, the motor configured to generate rotational motion to an output shaft of the motor; a pedal rocking mechanism coupled to the output shaft and driven by the motor, the pedal rocking mechanism being configured to translate the rotational motion generated by the motor to reciprocating rocking up and down motion of the at least one pedal about the rocking axis; and at least one bumper, height-adjustably coupled to the housing, located under and apart from a bottom portion of the at least one pedal, the pedal rocking mechanism comprising a camshaft coupled to the output shaft of the motor, a cam eccentrically coupled to an end of the camshaft, and a pedal coupling member coupled to an underside of the pedal, the pedal coupling member including a channel, the cam being arranged in the channel to convert rotational motion of the cam to reciprocating motion of the pedal coupling member so as to provide a positive application of force for driving the bottom portion of the pedal up and down towards and away from the at least one bumper, wherein the motor, the pedal rocking mechanism, the at least one pedal (10, 12) and the at least one bumper are configured so as to cooperate to, during operation of the motor, cause the bottom portion of the at least one pedal to tap against the at least one bumper at a bottom of a downward stroke of the pedal so as to provide pulsatile acceleration to the bottom of the user's foot, wherein the height of the bumper is adjustable to allow for tapping that provides pulsatile acceleration of about 0.1 g to 0.5 g, thus being sufficient to increase pulsatile shear stress to the endothelium, of sufficient magnitude to cause the release of beneficial mediators.