I’ve been reading off and on about interval training which, in short, is cardio training with short intervals of intense effort. I was browsing through some magazines at Barnes & Noble and a recent mention in Men’s [Health | Fitness] reinterested me in the technique. I checked online for some more information and found some useful articles at iVillage.
From what I've read, interval training can burn more calories in less time than traditional cardio. And the article “Invigorate with Interval Training” at iVillage has a good overview. As a starting point, they define exertion on a 1-10 scale with 1 being “very easy” and 10 being “very difficult”; and, they offer various interval training suggestions depending on your current fitness level:
For beginners, they recommend a 1:3 ratio of interval (at exertion 4-5) to recovery (at exertion 2-3). So, after a warm at low-middle effort for 5 minutes, you could go to a half-full effort for 2 minutes, return to low-middle effort for 6 minutes, and then repeat with the interval.
And, for intermediate fitness, they recommend a 1:1 radio of interval (at 4-6 exertion) to recovery (at 2-3 exertion). This one does have the advantage of being the easiest to keep track of times ;).
Then, for conditioned folks, their recommendation goes back to a 1:3 interval-to-recovery ratio, but with an interval intensity around 7-10. They point out that these intervals are called “anaerobic, because they are more like sprints and can't be sustained for a great amount of time on the aerobic energy system”.
Much of their examples focus on treadmills, but they add that easily adaptable to other machines such as exercise bikes and elliptical machines. I’ve been aware of interval training intuitively for some time, but I haven’t known the particulars on ratios and exertion. And, as I’ve only heard good things about this technique, I look forward to giving it a try next time I go to the gym.