Warming up before high intensity work is something I get a lot of questions about, but which I'm hesitant to offer too much advice regarding, other than to say 'warm up as needed'.

Personally, I spend very little time doing what most people would consider warming up. For many of my workouts, particularly interval ones where the rest interval comes first (some programs on machines are automatically structured this way), there is a bit of a built in 'warm up'. For others, however--tabata style intervals on the treadmill for example, or one mile time trials, there isn't. Here I usually do some sort of dynamic leg shakes, maybe a few knee ups, etc before starting. And although I'll certainly start out with a quick pace on such an effort, it won't be a 100 meter dash type pace and so physically (in terms of force of muscular contractions) it is well below the threshold where I worry about injury. But again, you may be different, and if in doubt it is certainly a better idea to err on the side of warming up too much rather than too little.

On this last point however, I need to mention that passive stretching should not be a part of pre-high intensity warm up. Get blood into your muscles with light activity, establish whatever neuromuscular connection you need to in order to ensure the mind-body synchronicity required for the upcoming effort, but DON'T include passive stretching. Sure a light bit of easy dynamic stretching is probably fine, particularly if you workout in the wee hours before your body has had a chance to loosen up naturally, but a full session of 1980's era 30 second at-the-edge-of-comfort-zone stretches will only increase the risk of injury when done preceding high intensity work (or, depending on who you ask, whenever it's done).