I don't know if I will do this cardio or the 42-minute one I'm so fond of but I cam across a good plan of attack for cardio. Again, it's with intervals (yes, I am enamored with the concept), and it needs to be done at a gym preferably so you can keep track of your heart rate.
Basically, you do this: warm-up for 4-5 minutes on any machine - treadmill, elliptical, bike, stairmaster - and then hit it hard. Go for 90 percent of your level, that is run an 8.5 sprint or go up to level 14 on the elliptical or as high as the stairmaster can go. Do that for two minutes, then rest for one minute. "Rest" can be a complete rest, that is get off the machine and stand around, or you can walk or do something easy. I'd probably walk on the 'mill or go to a gentle pace on the elliptical (I probably won't try this out on the other two). Then, go back for another 2-minute 90-percent session, followed by another minute-long rest session. In total, you want to do five rounds for a total of 15 minutes.
By doing this three times a week, you can greatly improve the amount of oxygen you can consume, which is apparently an important aspect of cardiovascular fitness. Also, you can increase your overall fitness level and increase the time it takes you to get exhausted.
Probably the most appealing part of this to me is the time element involved. 20-25 minutes is not a long time, and this is potentially even shorter. In 15 minutes of actual cardio time plus a few minutes warm-up on either side, you can accomplish great things.
I definitely want to try this. I went running this morning and I tried to run portions of my time in sprints but it was difficult to gauge just how fast I was running, how long I was running for and my heart rate. I have wanted to invest in a heart-rate monitor for some time now but until then I will use the gym machines for this.
The most difficult part, of course, is exerting yourself. Even if it's just two minutes, this sort of workout is challenging. Two minutes can seem like an eternity, especially if you are already exhausted and need to hit high gear. And I've been there many, many times, when I'm on the last leg of my intervals and I need to give it maximum effort and it's about the last thing I want to do. But it's in those times when you burn an enormous amount of calories and really make strides in your overall fitness.
To me, that's the most appealing part of interval training.