High intensity interval training is not a new idea, but you would think, with all the sudden attention it has received of late in the media, that someone had just discovered cold fusion. It's the cornerstone of any professional trainer's program, and it's part of the firmware of most modern treadmills and exercise cycles.

But trends will be trends, and how can you not take note of headlines like "1 Minute of All-Out Exercise May Have Benefits of 45 Minutes of Moderate Exertion" (in the New York Times, no less)? So with all the new hype, perhaps it's time to take a look at the actual science behind "HIIT."

First, the premise, in case you're just joining us: HIIT is just alternating periods of low or moderate exercise with more intense or extreme activity. Jog at a comfortable pace for a short time, then sprint all out like a rabid bear is chasing you. Coast down hill comfortably on a bicycle, then switch to Mt. Everest mode. Zumba along with Michael Buble, then try to keep the beat with your favorite speed metal band. You get the idea.

Why is HIIT better than, well, “no interval training.” It comes down to free radicals. When stressed by extreme exertion, certain among the chemical channels in the muscle cells that regulate calcium changes in the cells break down, and are flooded by free radicals. Calcium is critical for cell signaling, and the extreme demands triggered by the exercise prompt the cell to adjust its energy production and become more efficient. This increase in production and efficiency is your muscle cells' way of coping with the sudden duress.

It is worth noting that this spike is optimized for casual (or “non”) athletes. Seasoned athletes will have a much more difficult job of spooking their muscles by increasing their exertions, simply because their muscle cells have already gotten used to and tolerate more easily the “trauma” of HIIT and the body suddenly going gangbusters.

But for the more casual athlete, the benefits of HIIT can be dramatic. Tests have shown that the advantageous changes in muscle cells that adapted to but a single session of HIIT remain in effect 24 hours later. Researchers have concluded that the muscle cells are essentially “battening down the hatches,” changing in order to prepare themselves for further spikes of extreme exercise. They do this in order to “remember” how much energy they need and how quickly they need to produce this fuel in order to sustain themselves through the high—intensity engagements.