If you are already fitness-minded, you probably know there are several different ways to monitor your heart rate (HR, ie., the number of times your heart beats per minute) during your fitness activity of choice.

A lot of people are using HR monitors that strap around your chest and send the results to your smartphone or your watch. Watches such as Apple, Garmin, Fitbit or Polar can track HR by themselves. With the right model, you can encapsulate a specific workout and see your HR graph for that workout. That’s pretty cool!

These are all fine ways to capture HR. But before you do this, you need to know what a safe exercise target zone is for your age.

There are quite a few ways to find out. (Some require you to do MATH, for goodness’ sake.) Here’s a look at four methods:

1. THE AGE FORMULA

The tried-and-true method from the stone ages is the "age-predicted maximal heart rate" formula. You start by subtracting your age from 220 to get your maximum heart rate (HR Max). The idea is that HR Max declines with age.

Then you take a percentage of that to decide Target Heart Rate (THR). Our YMCA uses 60-85 percent to make this determination.

Depending on what type of training you are doing, that percentage can go up or down. For endurance training, it should be more towards the 60-70 percent range. For anaerobic training such as high intensity intervals, it should be more toward the 85-90 percent range.

For our purposes, we will talk about aerobic training. Here is an example. If you are 50 years old, subtract 50 from 220. Then multiply that times 60-85 percent.

220 - 50 = 170

170 x .60 = 102

170 x .85 = 145

So your THR is between 102-145. But wait! That assumes that everyone who is 50 years old should stay within these parameters. Not so fast.

Should a 50-year-old Ironman athlete and a 50-year-old couch potato be the same? Nope. Not even. Which leads us to ...

2. THE KARVONEN METHOD

Way back when, a Finnish scientist named Karvonen came up with a better idea. What if you put your resting heart rate (RHR) into the formula? That way, you can take into consideration what kind of shape your heart is already in. The lower your RHR, the less your heart has to work. So the Karvonen formula was born, also called the Heart Rate Reserve method.

To determine your true resting heart rate, take your pulse for a full minute before you get out of bed in the morning.

Using our example from earlier, let’s add in that our 50-year-old has a resting heart rate of 60 beats per minute.

220 - 50 = 170

170 - 60 (RHR) = 110

110 x .60 = 66

110 x .85 = 94

66 + 60 (RHR) = 126

94 + 60 (RHR) = 154

Now the THR increases to 126-154.

When a person’s RHR is considered, the zone in which they should exercise changes and is more accurate based on what kind of shape they are already in.

3. THE BORG SCALE

OK, all that is fine and dandy but slightly a pain to figure up. As time went on, we developed better and more efficient ways to determine what our HR should be while exercising.

Another choice widely used today is the Borg Scale, or the Rate of Perceived Exertion (RPE). Created by Dr. Gunnar Borg, the RPE chart goes from 6-20, with 6 being sitting and reading a book, and 20 being a very, very hard burst of activity that would be hard to maintain.

How do you feel while exercising? The goal is to feel like you are exercising in the 12-14 or 12-16 range, depending on the individual.

This scale is widely used in gyms. You may also see this scale as 0-10 instead of 6-20. If so, exercise within the 4-6 area of the 10-point chart.

This is a much better tool to use especially if you are on any medications that may slow down your heart rate, such as beta blockers that are prescribed for coronary heart disease.

4. THE TALK TEST

Even easier than all of that is something I use in my classes all the time: the Talk Test. If you cannot carry on a conversation while working out, then your HR may be too high. You should never be gasping for breath. You should be able to string a few words together before your next breath. This is a super simple way to tell how hard you are exercising.

So with all these options, you can decide. If you are into all the latest tech gadgets, a Fitbit, Garmin, Apple or Polar watch may be your chosen way to monitor HR. Is it accurate though? I have a Fitbit Charge HR and while I love it for steps and class competitions, the jury is still out about how accurate the mileage and HR are. Study up and read the reviews.

If you are not a tech person, just use the talk test or RPE, or get your calculator out and do the math. Either way, your target heart rate is something you should know as you take your fitness journey.

Ann Angell is a certified instructor and personal trainer and manager of the Oxford YMCA. She’s over 50. "Fitness over 50" is published the third Sunday of each month.