It's actually alternate picking;-) You should try playing four notes per string, it's very difficult when you start because of the shapes and banana finger syndrome but you will be amazed at how fast you can play . Also, 4 notes per string is even more economical DUDU DUDU DUDU, as opposed to DUD UDU DUD or more correctly (but more difficult) DUD DUD DUD. Give it a go for the practise excercise 1234, 1234, 1234, 1234 first to see the speed and economy of picking. Once you get the hang of it then try working out the positions for scales. All the really fast shredders use this technique as you can fit a lot more notes in over a six string run in about the same amount of time as three notes per string. Problem is the runs work diagonally up the fretboard, this adds to the difficulty of the shapes. Great practice though!