Intervals.

A curious word, that: the OED defines "interval" as "The period of time between two events, actions, etc., or between two parts of an action, performance, or sitting, two sessions of Parliament, etc.; a period of cessation; a pause."

Runners define "intervals" as "speed-work:" after warming up, you run very quickly for a certain time or set distance, then slow down briefly, then repeat as many times as required and/or possible before you expel your last pre-run meal everywhere. Funny how the actual word refers to the miniature breaks one gets between bursts, rather than to the bursts themselves-- though most runners seem to think of it as being the other way around (running between intervals of slowness, perhaps?).

Either way, the running version is challenging, to say the least. The plan I'm following called for a warmup, then three 1600-metre bursts of speed at a specific pace, with one minute's easier running in between. Much as I generally dislike running on a treadmill, the 'mill does at least have the virtue of consistency in pace: when you crank it, it stays cranked until you tell it to slow down. So unless I wanted to do a comic dismount of amusing but potentially injurious proportions in front of all the other gym-goers this morning, I had to keep up. I managed to do it, thankfully, but I certainly knew I'd been running when I was done. (Note to self: Time to put together a speed-training workout playlist for the iPod to keep me properly distracted on Wednesdays.)

I must admit, the feeling of accomplishment when I got off the treadmill after a cool-down was delightful, even if my legs were demanding, "What on earth was that for??" I told them to get used to it, and proceeded to my new strength-training and core routines to underscore the point. They quit complaining. (Tomorrow, however, may be another story: Revenge of the Quads, coming soon to an early morning near you.)