A method and apparatus are provided for implementing automatic congestion avoidance for differentiated service flows in a communications network. To exercise, the user grasps one or two units, imitates the motions of swinging a conventional jump rope, and jumps up and down, but there is no risk to the user of tripping over a rope as with a conventional jump rope. The invention also describes a lighting assembly comprising a semiconductor light source arranged on a substrate ; a collimator realized to enclose the semiconductor light source ; and an actuator for moving a hinged side wall of the collimator over at least part of its range of motion to adjust the light exit opening of the collimator. The clips are spring biased to grip the second conductor at a plurality of locations and hold the second conductor in electrical interengagement with the contact component. Determination that the defibrillation pathway is shorted may be made by conventional low current measurements or delivery of high current extremely short test pulses.