Interval exercise helps to reduce workout time while providing the body the added boost to a workout that it needs to be "overloaded" - which is when it will respond better to your efforts of working out. There is a "Work to Rest" ratio that is followed. Please enjoy the interval options I've provided below:
INTERVAL ONE:
5 min warm-up
5 min: 15 second- max effort; 45 seconds rest
5 min: 30 second max effort; 1:30 seconds rest
5 min: 1 min max effort; 3 min rest
5 min cool down (add in 5 minutes of ab work before you head home)
INTERVAL TWO
2 to 5 minute warm-up
Work Hard 10 seconds; Rest for 30 seconds
Repeat for 15 minutes
Cool down 5 minutes
INTERVAL THREE
Warm Up- 2 to 5 minutes or jump rope or jumping jacks to get the heart pumping and sweat flowing
Start with a moderate pace on your machine (Treadmill - 5mph jogging for example) for 1 minute.
Increase 2 levels of resistance and maintain that increase for 1 minute, increase by two levels 3 more times each holding for one minute, and come back down the same way you came up, repeat the full increase/decrease cycle.
Cool Down 2 to 5 minutes.
INTERVAL FOUR: (provided by K. Sanborn)
This is great for runners who want to work on increasing stamina and pace. For those using elliptical, find a good "difficult" pace that you can maintain for the first 6 minutes, and then increase that difficulty as the interval times get shorter. Work to Rest ratio looks like this (work:rest).
Warm up:
5 to 10 minutes
6:3
5:2
4:2
3:1
2:1
3 min walk
1:1
2:1
3:2
4:2
6: cool down.