"Position one dumbbell over head with both hands under inner plate or with the bar, comfortable grip as close as you can get without the wrists bending out, keep them straight, elbows straight.. you can sit or stand. With elbows over head, lower forearm behind upper arm by flexing elbows. Flex wrists at bottom to avoid hitting dumbbell on back of neck. Raise dumbbell over head by extending elbows while hyperextending wrists. Return and repeat." - That's not a tricep pushdown, that's an overhead dumbbell press. A lot of power racks come with a pulley system with high and low pulleys allowing you to do pull downs, press downs, rows etc. as opposed to the rack shown in the article above which is just the basic frame.