A common way to determine how intense your workout is, is to measure your heart rate (HR). The faster it beats, the more intense the workout.

In order to determine how fast you want your heart to beat during exercise for optimal weight loss, you first need to calculate your maximum HR. Your maximum HR is what is the maximum beats per minute your heart should beat during exercise. The formula to calculate your maximum HR is 220 minus your age. So if you’re 35, your maximum HR is 185. Please note that this is a simple formula that doesn’t take into account your fitness level. At the bottom of this page, I’ll write the formula for finding your HR zones using your resting HR (the fitter you are the lower your resting HR is).

Once you know your maximum heart rate, you can calculate your desired target heart rate zone — the level at which your heart is being exercised and conditioned but not overworked.

1. Recovery zone (aerobic): Training at 50%-60% of your maximum HR. In our example, that means 93-111. In this zone, your body will improve its blood flow.
2. Endurance zone (aerobic): Training at 60%-70% of your maximum HR. In our example, that means training 111-130. In this zone, your body will increase its ability to use fats and carbohydrates, and improves your endurance.
3. Stamina zone (aerobic): Training at 70%-80% of your maximum HR. In our example, that means training at  130-148. In this zone, your body’s ability to use oxygen and its muscles strength  will increase.
4. Economy zone (anaerobic): Training at 80%-90% of your maximum HR. In our example, that means training at 148-167. In this zone, your body’s efficiency will improve but it is hard and is recommended only for short period of times.
5. Speed zone (anaerobic): Training at 90%-100% of your maximum HR, should be performed only by experienced athletes and for short bouts.

Important: If you’re taking high blood pressure medication consult with your doctor to find out if you need to use a lower target heart rate.

If you’re only starting out, start slowly, at about 50% of your maximum HR. You need to gradually build up the intensity as your aerobics abilities improve.

So how do you measure your heart rate while exercising? Many treadmills, ellipticals, etc. offer built-in HR monitors. You just need to hold your hands on the metal handles for a few seconds, and your HR shows up on the monitor. I recommend however that you invest in a good heart rate monitor. The more accurate ones have a separate chest strap that you put around your chest. I prefer the Polar brand, they’re very reliable and easy to use. If you look on Amazon, there are so many models to choose from, such as this one. Just look at the different features (and your budget!) and see what features you think you will use most.

Last but not least, as promises need to be kept, this is how to calculate your workout zones taking into account your resting HR:

1. Calculate your maximum HR (220 minus your age). If you’re 35, your max HR is 185.
2. Find out your resting HR: When you wake up in the morning and still in bed, put your index and middle fingers on the artery on your wrist or neck, and count the number of beats in one minute. Alternatively, count how many beats in 10 seconds, and multiply that number by 6.
3. Calculate your Heart Rate Reserve (HHR): Subtract your resting HR from your maximum HR. If you’re 35 and your resting HR is 65, your HHR would be 120 (185-65=120).
4. Calculate your Aerobic Training HR Range: Calculate 50% and 80% of your HHR. In our example, you will get 60 and 96 (120×0.5=60 and 120×0.8=96). Now add these numbers to your resting HR. You get 125 (65+60=125) and 155 (65+96=161). This zone (125-161) will give you the zone in which you will burn the most fat.