Knowing to work out within your targeted heart rate zone can help athletes reach their goals quickly. It is however important to know how much one can push to ensure that one does not make exercising unsafe and leads to injury.
Intensity, frequency, and duration are key components to take care of when doing any cardiovascular exercise. Hence, it is important to know your heart rate to judge the intensity of your exercise.

Determine Maximum Heart Rate (MHR)
Every athlete must know their maximum heart rate (MHR). Once this number is determined, athletes can gear their workout to the right intensity levels. MHR varies for each person.
The easiest way to determine MHR is by subtracting your age from 220. For Eg. if you are 30 years old, then your MHR will be 220-30 = 190 bpm.

Determine Target Heart Rate Zones
Exercising in different heart rate zones can lead to different benefits. The heart rate zones are classified based on the percentage ranges of MHR. In each zone the exertion levels are different and the body burns carbohydrates, protein, and fats differently.

Very Light Workout Zone- Under 57% MHR
This is a mostly sedentary or very light activity the person is engaged in. The ability to talk is not all hindered.
For athletes, it is important to train in this zone, if you have finished participating in a very intensive event and are recovering from it.

Light Workout Zone: 57% to 63% of MHR
In this zone, breathing will get slightly heavier, but talking will not be hindered and is considered a comfortable zone to exercise.
Workouts are less intense, without any cardiorespiratory benefits.
In this zone, the body will derive its energy from fats primarily (85%), carbohydrates (10%), and protein (5%).
Walking as an exercise falls in this zone.

Moderate Workout Zone: 64% to 76% of MHR
In this zone, breathing gets heavier, and talk comes down to short sentences. Calories burnt is slightly more than the Light Workout zone. In this zone, the body will derive its energy from fats primarily (85%), carbohydrates (10%), and protein (5%).
Brisk Walking as an exercise falls in this category.

Vigorous Workout Zone: 77% to 95% of MHR
In this zone, breathing is very hard and talking comes down to short phrases. When training for endurance, this is a zone all athletes must aim for. 20 minutes to 60 minutes of workout in this zone can lead to significant improvements in the body's circulatory system, with improvements in heart and lung capacity. As the intensity is higher, the calories burnt will be higher. Significant improvement in the VO2 max can be achieved if training at 84% of MHR or greater. Elite runners, cyclists work out in this zone to go faster.

It is important to note that the body uses carbohydrates more (85%) fat (15%) and protein (less than 1%) when working out at 84% of MHR and higher. Workouts in the higher ranges ( 84% of MHR and higher), should be done in an interval range of 10-20 minutes.

Maximal Workout Zone: 96% to 100% of MHR
In this zone, the person will be gasping for breath and will not be able to speak. Athletes should train in this zone for a few minutes and drop this intensity down for several minutes and then repeat.
In this zone, the body burns carbohydrates (90%), Fats (10%), and Protein (less than 1%).

Monitoring Heart Rate:
Most treadmills and exercise machines will have a grip with pulse sensors built in that indicates the HR on the display of treadmills. Smartwatches coupled with apps can be used to track HR. Heart rate monitors with a chest trap are more accurate in measuring Heart rate.

It is recommended that athletes vary their workouts and allow a recovery day between days of intense workouts, especially when exercising in the higher end of the MHR to maximal MHR.