Some casually browse the pages of old magazines, read the latest thriller or chat with friends as they dutifully put in their "forty five minutes" of "slow and steady". They are well-intentioned but clueless. I question the results of their efforts but decide it is unwise to offer unsolicited advice.

One lady, however, is focused and pays attention to what she is doing. She periodically refers to the treadmill's glowing red display and adjusts her pace accordingly. Good for her! She is monitoring her heart rate.

What she knows, that the others don't know, is that your Heart Rate is a dead accurate indicator of just how hard your body is working. This is the best way to make sure that you are exercising vigorously enough to improve your fitness level but not so hard as to overexert yourself.

This is also a great way to lose weight and get really fit in the shortest amount of time. What you have to do is exercise at the correct intensity within an optimal range. This is your Target Heart Rate (THR) which is expressed as a percentage of your Maximum Heart Rate (MHR).

You can calculate your personal Target Heart Rate, but this gets a bit tricky. You have to know your Resting Heart Rate (RHR) and plug it into a couple of formulas: (MHR – RHR X (50% - 80%) + RHR = THR) where (Age – 220 = MHR).

You also have to know how long to exercise, at which point in the optimal range (50% to 80%) and you have to monitor your heart rate while you are working out. There are charts that estimate your THR for you but their accuracy can vary, up or down, by as much as ten percent.

Confused? Don't be. Dump the math and take a low-tech approach. You already have a simple, built-in heart rate monitor that is perfectly calibrated to your body.

And, you already know how to use it because it's as simple as watching your breathing. Your respiration rate is how you monitor the intensity level of your exercise and it relates very closely to your actual Heart Rate. You can use this method with any piece of gym equipment and while walking or jogging outdoors.

WHAT YOU NEED TO REMEMBER is that, as your workout progresses, you may exercise at any one of three levels or zones. I will describe each zone and relate Heart Rate to how hard you will be breathing.

ZONE 1. (50% - 65% OF MHR) Breathing is normal at this level and you can easily carry on a conversation with a workout partner. This is your warm-up and cool-down zone which will do little to get you fit unless you are very overweight, very out of shape or have been ill.

ZONE 2. (65% – 80% OF MHR) Your breathing becomes somewhat to very noticeable. This is your training zone where you will do most of your work, develop cardiovascular fitness and burn calories. At the lower end of the range (65%), you will be able to speak to a partner easily but your speech is somewhat broken as you deliver phrases between breaths. At the top end (80%) you will be breathing very hard. Though conversation is possible, breathing may be your priority.

ZONE 3. (ABOVE 80% OF MHR) Entering zone three, you begin panting and gasping for breath. This level can be hazardous for many of us and is best reserved for competitive athletes.

TO GET FIT IN THE SHORTEST AMOUNT OF TIME, DO THIS:

1. Tell your doctor that you are going to begin exercising at a level where you will be breathing vigorously. Ask if, based on your physical condition, you should limit your effort and if so, to what level.

2. Warm up at a conversational pace and then increase your speed or intensity level to 70% - 75% of MHR (breathing strongly) so that after about five minutes you feel fatigue setting in. Back off and catch your breath at 65% of MHR or below.

3. Now really pick up the pace (fit walkers find a hill) and push to 75% to 80% of MHR (breathing vigorously). Hold it there, from one to three minutes, until your body is asking for a break and then slow down to 60% of MHR, or below, until you recover.

Repeat, gradually increasing the number, duration and intensity of intervals as you are able. If you challenge yourself to work hard your workout should, at most, take no longer than thirty minutes.

Cool down and have a refreshing drink of water. These interval workouts, using your breath to gauge intensity will work very effectively to burn calories and get you in shape.

And always remember "Be Strong…. Be Lean"