We are always looking for a big bang for our exercise buck. We want to burn fat, increase muscle, improve our cardiovascular system, and do it all in the shortest time possible. After all, we can't spend our precious hours in the gym - we have a million other things to do! One of the most efficient ways to train that incorporates all of these requirements is interval training. Part One of this series will teach you the basic principles of interval training and how to modify your cardiovascular workouts into interval training workouts. Make sure that you pick up the next issue of Muscle and Fitness Hers for Part Two, which instructs you how to turn your weight-training workout into an interval-training workout. You don't need to go postal by spending hours running or biking to get the body you want; go interval and realize that the road to your best shape may take less time than you thought!

What is Interval Training?
Interval training involves sets of repetitions (intervals) that are performed at variable exercise-to-rest ratios [1] or work-to-recovery ratios (WRR). An exercise interval is a continuous multiple sequence or whole body activity of supramaximal intensity. Because intervals are so intense, they can only be performed for a short period of time. Beginners should start their intervals at 10-15 seconds and can progress up to 30-90 second intervals, but not exceed more than 120 seconds per interval. If you can go that long, you're probably not exercising hard enough! That means you have to get your butt in gear girls, and move quickly and intensely during an interval workout. One benefit of interval training is that you will practically cut your exercise time in half - but it will seem like you doing even more work because of the speed and intensity of the workout.

Why Should I Go Interval?
We used to think that exercising at a low intensity for a long period of time would burn the most fat. I'm even willing to bet that most women still think that 45-50 minutes of stair stepping at a moderate pace is the ideal way to lose body fat. But it's time to step into the 21st century, ladies, and read the research on the wall. Many studies are now proving that as exercise intensity increases, total energy expenditure is increased [2]. And get this: with higher intensity exercise, there is a stimulation of fat stores. Other studies proved that although an endurance training program burned more calories, a high-intensity interval training program burned more fat [3, 4]. In fact, in these studies, the interval training group lost fat at a rate that was nine times that of the endurance group! In addition, the studies showed that not only did the interval group gain lean body tissue (muscle) while losing fat, but they also did it in less time per exercise session (30 minutes compared to 45 minutes) and in less weeks (15 weeks compared to 20 weeks). With the increase in lean body tissue and the extra postexercise oxygen consumption needed from the additional energy expenditure, metabolic rate throughout the day will also be elevated. Think of it as quality versus quantity. You can spend 45 minutes of your valuable time on the stair machine at Level 4 and burn some calories while you are stepping away, or you can invest 20 minutes doing stair intervals at Levels 4 and 7 and burn some calories during the exercise, and then burn even more throughout the day. But the real goal in exercising to lose body fat should concentrate on that fact - burning body fat - and not the amount of calories burned. It makes perfect sense, right? Then why do we consider all of the long, slow "cardiovascular" exercise we do to be fat burning, when it actually is just calorie burning? As Conrad Earnest, PhD,CSCS, Exercise Physiologist at the Cooper Institute explains, "Long, slow distance exercise is often recommended because it is simple, safe, and the proportion of fat used to fuel the exercise is greater than during high intensity exercise. But, don't let that fool you. Assuming all safety related issues as a given, it isn't the proportion of fat burned that is important for weight loss, it is the quantity of fat!" Unfortunately, long, slow endurance exercise is also muscle burning, too. Why do we work so hard lifting weights to increase our muscle just to eat it up during a long, slow cardiovascular session? And when you lose muscle, girlfriend, you decrease your body's resting metabolic rate (RMR). This means that you must decrease your calories even more to maintain or lose weight. Who needs that? We are depriving ourselves of food already!

How Do I Go Interval?
The key to changing your cardiovascular-endurance workout into an interval session relies on the intensity of the work and the work-to-recovery ratios (WWR). It is always a good idea to consult a physician before beginning any new exercise program, especially one as intense as interval training. According to Dr. Earnest, interval training more than three days a week will likely lead to overtraining and injury. Remember the motto with interval training: quality not quantity. Apply the motto to the length of your interval session, also. A five-minute warm-up, 5-minute cool-down, and 20-30 minutes of intervals is really all that you need. The fun of interval training comes in designing your interval program. Since there are no hard and fast rules, you can vary the WRRs to accommodate your level of fitness and your personal preferences. It is easy to incorporate variety and eliminate boredom when you are speeding up and slowing down at different time intervals. For instance, you can choose a WRR of 1:1 where you are exercising at a high intensity for a certain amount of seconds (let's say 10 seconds) and recovering for the same amount of time - 10 seconds. If the WRR is 1:2, you would be exercising intensely for 10 seconds and recovering for 20 seconds. The longer your work interval is and/or the more intensely you perform it, the longer your recovery needs to be. So, if your work interval is up to 120 seconds (2 minutes), you may need a recovery interval of 600 seconds (10 minutes). That's a WRR of 1:5. When your fitness level increases, progression can occur with decreasing WRRs. So even if you are exercising intensely for 30 seconds, you may only need 30 seconds to recover. It's nice to have a good aerobic base for interval training, but actually, resistance training may be even more important to prepare the muscles for the high power production necessary [1].

Let's Get Interval
So are you ready, girls, for what may be the toughest, most efficient workout you've ever had? I know that you are ready to decrease your time in the gym, yet get even better results from your fat-trimming efforts. It's time to base your fat-loss goals on some real research and not from the old wives' tales that slower is better. Kick it up a notch and get intense with interval training. As Dr. Earnest says, "All you have to lose is a little extra fat!"

Sidebar - Interval Training for outdoor steps or stadium bleachers
You can use stadium bleachers found on high school or college campuses, or you can use regular steps or stairs. Choose your work as walking or running up the steps and your recovery as walking or running down the steps. Beginners should start with walking one step at a time with their arms at their sides, then with arms overhead. Progress to running, then taking 2 steps at a time for a more intense work bout. Always begin with a five-minute warm-up and end with a 5-minute cool-down. Gauge your work and recovery ratios by either the heart rate method or RPE method (see sidebar).

Sidebar - Interval Training for indoor bicycle or treadmill
You can simply use an interval program or hill program on the standard computerized bicycles found in most gyms for an interval workout. The tension on the bicycle will increase during the work bout while you try to maintain a high RPM, and decrease during the recovery bout. Of course, you can also do this manually if you prefer to control your WRR. Another way to make the work bout more intense is to crank it up to the highest level of tension and stand up and ride the bike without your bottom touching the seat, but still trying to maintain the same RPMs. Does this sound like one of those indoor cycling classes? It is true that most of these classes incorporate intervals. Some treadmills are also programmable, but most require a manual adjustment. You can choose a walk:jog, walk:run, walk:sprint, or jog:sprint, run:sprint WRR, depending on your level of fitness. The incline on the treadmill is also a nice way to progress the intensity of the work session. See the Methods to Measure Intensity Sidebars.

Sidebar - Methods to Measure Intensity - Heart Rate Maximum
This method is a little difficult and sometimes inaccurate because heart rate doesn't always correlate with effort, but if you wear a heart rate monitor it will simplify things. For safety for beginners, using the age-predicted maximum heart rate formulas and a heart rate monitor to assess your intensity is essential. To determine a percentage of your heart rate to work at for your intense work sessions, calculate your age-predicted maximum heart rate (APMHR) and multiply it by the appropriate percentage. The American College of Sports Medicine recommends staying between 60%-90% of APMHR for work sessions. For a beginner, work ratios should be between 60%-80% of APMHR and then can progress up to 85%-90%. Example for a 30 year-old woman beginner who wants a 70% work bout:
APMHR = 220 - age (220-30) = 190 x .70 = 133
You can also arrange the heart rate percentage to reflect your selected recovery heart rate. Let's say that our beginner wanted to recover at 60% of her APMHR.
APMHR = 220 - age (220 -30) = 190 x .60 = 114
Then she wouldn't begin her next interval work repetition until her heart rate had recovered to 114 beats per minute.

Sidebar - Methods to Measure Intensity - Ratings of Perceived Exertion (RPE)
This method allows you to measure intensity and effort by the way it feels to you and then giving it a number. Some use a 15-point Borg scale with a 6 being no exertion and a 20 being maximal exertion. A Category-Ratio scale can be used with 0 being nothing at all and 12 being absolute maximum. But let's simplify things and rate effort on a 0-10 scale, where 0 is no effort and 10 is maximal effort. We can then correlate these to percentages and say that a 5 is 50% effort and that a 10 is 100% effort - you can't do any more than that. A 5 is where you should be at the end of your warm-up, a 3 at the end of your cool-down, and 9-10 for advanced interval trainers during a work session. For example, a beginner should warm-up at 5, work at 6-7, recover at 5-6, and cool-down at 5-4-3. Intermediates should warm-up at 5, work at 7-8, recover at 6-7, and cool down at 5-4. Advanced trainers can warm-up at 5, work at 8-9-10, recover at 7-8, and cool-down at 5-4.

References
1. Plisk, S.S., Anaerobic Metabolic Conditioning: A Brief Review of Theory, Strategy and Practical Application. Journal of Applied Sport Science Research, 1991. 5(1): p. 22-34.
2. Williford, H.N., M. Scharff-Olson, and D.L. Blessing, Exercise prescription for women. Special considerations. Sports Med, 1993. 15(5): p. 299-311.
3. Tremblay, A., J.A. Simoneau, and C. Bouchard, Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism, 1994. 43(7): p. 814-818.
4. Tremblay, A., et al., Effect of intensity of physical activity on body fatness and fat distribution. Am J Clin Nutr, 1990. 51(2): p. 153-157.