Interval runs are among my favorite workouts. The benefits of interval training are numerous and pretty darn convincing, but for me they basically provide an efficient way to make the most out of my (minimal) time. This high-impact, yet manageable routine takes under 30 minutes and, if you're into that sort of thing, will burn way over 500 calories (not even counting the rest you'll burn afterwards).
After watching top trainers in Los Angeles a few years back do some crazy stuff on the treadmill in their precious few minutes in between clients, I made some friends, asked around, shook some hands, kissed some babies, and finally achieved a minute-by-minute rundown of what the heck they were doing and why they swore by it. Since then, I've changed and adapted it to fit myself. Here's exactly what I do:
Start the treadmill in manual mode. You'll be in charge. Set it to a normal jogging (not fast walking) speed (S). For now, let's say that's 6.5 mph. This is your warmup.
00:00 - 02:30 Warmup jogging as usual at S6.5 (or until you're loose).
02:30 - 03:00 After warming up, stand on the siderails. Transition the treadmill to incline (I) 9 (or higher) & S9 (or higher). These can go up as you get more comfortable or on days you feel better (or even depending on the machine). Some people advise setting the incline high as the treadmills allows. That's awesome. But not necessary.
03:00 - 03:15 Jump on (make sure you've done a few test strokes with one food so you have a good sense of how fast it's going) and sprint as fast as you can for 15 seconds.
03:15 - 04:00 Jump off the belt and back onto the siderails. Breathe. Enjoy the break. That was fast, but you can still easily catch your breath. Do not worry. This will change.
04:00 - 04:15 Complete your second 2nd 15 second sprint.
04:15 - 05:00 The 2nd break.
05:00 -05:15 The 3rd 15 second sprint.
05:15 - 06:00 3rd break.
06:00 - 06:15 4th 15 second sprint.
06:15 - 07:00 4th break.
07:00 - 07:15 5th 15 second sprint.
07:15 - 08:00 5th break.
08:00 - 08:15 6th 15 second sprint.
08:15 - 10:00 Biiig break. You're gonna repeat the 6x short-term intervals you did before, but now with 20 second sprints & 40 second breaks.
10:00 - 10:20 1st 20 second sprint (still at the same #s you had before, I9 & S9— or wherever you've moved this to).
10:20 - 11:00 1st 40 second break (still standing on the siderails).
11:00 - 11:20 2nd 20 second sprint.
11:20 - 12:00 2nd break.
12:00 - 12:20 3rd 20 second sprint.
12:20 - 13:00 3rd break.
13:00 - 13:20 4th 20 second sprint (should be a real challenge to muster up the necessary energy by this point).
13:20 - 14:00 4th break.
14:00 - 14:20 5th 20 second sprint.
14:20 - 15:00 5th break.
15:00 - 15:20 6th (and FINAL!) 20 second sprint.
15:20 -17:00 Biiiig break. Woah. Tough part's over.
17:00 - 17:30 30-second long sprint... but you can't use your arms. Hold the rail in front of you and just pump those legs. Make sure to keep your hips under your chest & control your breathing.
17:30 - 18:30 Rest on the siderails. Breathe a lot.
18:30 - 19:00 2nd 30-second sprint (again, no arms).
19:00 - 20:30 Breathe. Transition the treadmill back down to that jogging pace (S6.5, for example) and then match that with the incline, so I6.5.
20:30 - 22:30 1st 2-minute jog. This should seem way easier, at least relative to what you've been doing. But it's for endurance... and should be tough, but manageable, too.
22:30 - 23:30 Rest.
23:30 - 25:30 2nd 2-minute jog.
25:30 - 26:30 Rest.
26:30 - 28:30 3rd 2-minute jog.
28:30 - 30:00 (or whenever) Walk it off. I usually put the treadmill down to I0 and S4 and walk as long as I feel like it.
And you're done. 30 minutes. You never have the time to get bored (or do anything else, really, but watch that timer). I also think it's an awful lot of fun. The real key? Ignore everyone else. You should be huffing and puffing, stopping and starting, and basically running as fast as you possibly can for short bursts... which looks kind of silly compared to, oh, everyone else in the gym who's jogging at a steady pace. Don't worry. They're impressed. They didn't even know someone could run that fast!
*The speed and incline numbers are flexible. Choose what works best for you and then slowly work up. I started at S8 & I8 and am now, depending on how I feel that day, hovering around S10 & I10. To make it easier, increase the rest times (or, to make it harder, decrease them). But intervals are all about pushing yourself as hard as you can knowing there's a break right around the corner.
*Also, some treadmills are set to stop 20+ seconds after they've realized there's nobody on. Don't worry. Just hit the button it suggests you press and/or pump one leg on it every 20 seconds or so and the treadmill will remember you're on there (and killing it).
*This can also be applied to nearly any other cardio exercise, from the elliptical to the bike. This routine was built for the treadmill, but find whatever you like doing best and stick with it!