We all have a heart and as long as we are alive, it is beating.

But is that all the beating tells us, that we are still alive?

Actually no, it can tell us much more if we pay attention.

At rest it can give us an idea of how hard our heart is working as well as clues about our state of health, stress, and fitness.

During exercise it can help us to understand the intensity of our workout. Here, too, it can also give us important information regarding our health as well as indications of how well we recover within, and between, workouts.

It can alert us if we are not recovered from an illness, if we aren’t hydrated properly, if we aren’t adapted to heat, humidity, or time zone changes.

All pretty cool things if you ask me.

In the past we have discussed the effect of overtraining on heart rate (you can review that here) but today we will look at heart rate as it relates to exercise.

Heart rate and exercise

Usually when we hear about heart rate and exercise the recommendation goes as far as ‘get your heart rate up’ and that is pretty much it.

Is it enough to say ‘get your heart rate up’?

How high is ‘up’?

Should you aim to get it as high as possible?

Should you do that every time you exercise?

Why does any of this even matter?

All great questions which we will answer, but to give you the bigger picture heart rate during exercise helps us to determine our exercise intensity.

The intensity of our exercise will dictate the adaptations that our bodies must make. In a nutshell, exercise intensity determines results.

Often when we discuss exercise and exercise intensity we use the terms Intense Cardio Exercise (ICE) and Low Intensity Activity (LIA). These terms allow us to broadly categorize our exercise- is it intense or not?

Using heart rate to determine exercise intensity allows for more specific exercise prescriptions to be made. This is important when it comes to improving fitness and fat loss as well as returning to exercise after illness or injury.

To determine exercise intensity using heart rate we typically compare an individual’s heart rate during exercise to their maximum heart rate. We then say that they are exercising at a certain percentage of maximum heart rate, or %HRmax.

In order to do this there are a few things we need to consider.

It is critical to know maximum heart rate- the number of times your heart beats per minute during the most intense exercise you can tolerate.

Simple enough, right?

Definitely sounds that way, but the only truly accurate way to determine your maximum heart rate is to measure it directly. This is typically done in a lab setting using a metabolic cart.

Since this isn’t something that everyone has access to formulas have been developed to calculate, and estimate maximum heart rate. One simple formula is to subtract your age from 220.

Keep in mind that this is just an estimate and that it may need to be adjusted. The inherent error in using this formula may leave us with an estimated maximum heart rate that is 12 beats per minute higher or lower than the actual maximum heart rate.

From there we need to know what intensity of exercise we want to perform.

As an example let’s say I wanted to exercise at 60% of my max heart rate.

If my maximum heart rate is 178 BPM then exercising at 60% of my HRmax would be at a heart rate of 106 beats per minute.

Target heart rate= 178 x .60

As I mentioned using the 220-age formula to determine heart rate max has inherent error in it. In order to minimize the error it may be best to take things a step further and include resting heart rate into the equation.

To do that we can use something called the Karvonen method.

The Karvonen method is the preferred method to determine heart rate range during exercise if we do not have a direct measure of max heart rate. (Meaning you did not perform an exercise test in a lab using a metabolic cart to determine HRmax.)

This method utilizes heart rate reserve (HRR)- or the difference between maximum heart rate and resting heart rate- to determine a target heart rate for exercise.

HRR= HRmax- HRrest

Resting heart rate, just like max heart rate cannot be used to indicate cardiorespiratory fitness. In other words, it is important to realize that a higher HRmax, or lower resting heart rate, doesn’t necessarily translate to a more fit person.

How to determine intensity for exercise

Ok, so mathematically we can determine what our heart rate should be when we are exercising at a certain intensity, but how are we to choose the intensity at which we should be exercising?

The American College of Sports Medicine (ACSM) recommends exercising at 40/50% to 85% heart rate reserve, or 55/65%- 90% HRmax, for healthy individuals.

Intensities in the lower range may be useful for improving health measures in sedentary or older individuals while 60-80% of heart rate reserve (or 70-90% HRmax) is prescribed for improving cardio respiratory fitness.

It should be noted that the more fit an individual is, the higher the exercise intensity needs to be in order to continue to produce results.

Target HR= [%exercise intensity x (HR max-HR rest)] + HR rest

So, if my resting heart rate is 57 bpm (beats per minute) and my max heart rate as calculated using 220- age is 178 bpm I can use these to calculate my target heart rate.

For a lower intensity of 50% heart rate reserve the calculation would look like this:

Target HR= [.50 x 121] +57
Target HR =118

This would be considered low intensity activity (LIA).

If we utilize this same formula and calculate a heart rate range for 70-85% of heart rate reserve we would have a range from 142 BPM to 160 BPM.

This would be considered an appropriate range for intense cardio exercise (ICE).

Maximum heart rate is not something that can be improved with training. In fact it changes very little.

What we can change is the percentage of our max heart rate that we can maintain for extended periods of time. Being able to function at a higher percent of HR max for longer followed by faster recovery is a sign of improved fitness.

An indicator of fitness is the percentage of HRmax that can be maintained for extended periods of time.

The only way to achieve this improvement in fitness is to exercise at an intensity that stresses the cardiorespiratory system; in other words- at the right intensity.

In healthy individuals low intensity activities will not improve fitness. Low intensity activities such as leisurely walking, gardening, or cleaning the house can have a positive impact on health but will not improve fitness and will likely do very little to improve fat loss.

A heart rate monitor is the best way to monitor intensity during exercise. Models vary so be sure that yours can be programmed with your specific information; age, gender, weight, height, HRmax, HRrest are all important parameters and should be included.

Without a heart rate monitor, is there any way to know how hard you are exercising?

No heart rate monitor, no problem. Well, sort of. This is where you need to be really honest with yourself and those around you. How hard do you feel like you are working?

Adapted from Brooks, Fahey, Baldwin 2005.

We can use intensity ratings (IR) to give us an idea of our exercise intensity. The Metabolic Precision IR scale parallels the modified Borg scale.

The major challenge here is realizing how hard you are capable of working. Too often people underestimate their ability and end up falling short in the intensity department hindering improvements in fitness and fat loss.

Should you always aim to be at your maximum?

No, not always. Remember, we talked about ranges of intensity. A portion of your exercise session may be spent at a lower (relative) intensity. Not a low intensity, but lower than your heart rate max.

Intense Cardio Exercise (ICE) will have points during which your heart rate nears its maximum. These periods may last from 10 seconds to maybe one minute. Anything longer than that and you aren’t at your maximum.

Using this type of work- rest interval training means that you can successfully complete more work, and more work at a higher intensity than you could if you removed the ‘rest’ interval.

The American College of Sports Medicine released updated exercise guidelines in 2008. In these guidelines they specifically note that exercising at higher intensities decreases the amount of time necessary to notice health and fitness benefits.

Many studies highlight the importance and effectiveness of high intensity training.

One study found that 15 minutes of intense exercise gave the same all-cause mortality risk reduction as 60 minutes of moderate intensity exercise [3].

Yet another showed that completing one high intensity session per week resulted in the same or even higher all-cause mortality risk reduction compared to several hours of moderate intensity exercise [4].

What does this mean for you?

1. Maximum heart rate (or resting heart rate) is not in and of itself an indicator of fitness

2. Using formulas to calculate maximum heart rate may result in a heart rate 12 BPM higher or lower than actual. Testing in a lab setting is always preferred.

3. Exercising at specific intensities yields specific results (ie improvement in fitness). When planning an exercise session the goal isn’t just ‘max out’ with regard to heart rate.

4. The ability to exercise for prolonged periods at a high percentage of maximum heart rate is an indicator of fitness.

5. Exercising at or near maximum heart rate in every training session may lead to injury. This is often due to lack of adequate recovery.

6. Elevated resting heart rate may be indicative of inadequate adaptation, inadequate recovery, or illness.

7. Some medications may elevate heart rate while others may keep heart rate from rising. If you are on any medications please discuss their potential heart rate effects with your doctor.

Without a clear definition and clarification the word ‘intense’ can be confusing or even scary. Read this great article here to gauge and define your intensity to ensure your cardio become a potent fat loss weapon.

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