It's a familiar scenario: you're spending every morning at the gym, and resisting sweet treats — but you still can't shake those stubborn extra pounds. 

An increasing body of research suggests you may be making one crucial mistake, which can be easily rectified using your fitness tracker. 

Fitness experts say one key way to optimize your calorie burn is to ensure you reach a specific heart beat range while you workout.  

This fat-burning window differs depending on multiple factors, including your age, stress levels, medication you're on and how much coffee you've drunk.

Below, a DailyMail.com chart reveals the range you should aim for in your next workout for faster weight loss.  

The ideal average resting heart rate is between 60 and 100 beats per minute, though several factors can cause it to increase, including exercise.

The maximum heart rate is the highest number of times a person's heart can beat per minute without causing stress on the organ. 

This is based on age and tends to decrease over time.

The main way to determine your maximum heart rate is to subtract your age from 220. For example, a 50-year-old would have a maximum heart rate of 170. 

Exercising uses energy, with more intense exercise burning more energy and increasing heart rate. 

As intensity increases, your body has to use fat stores for energy instead of sugars and carbohydrates. Doing this consistently helps burn fat and lead to weight loss. 

This is known as your fat-burning heart rate, which is roughly 70 percent of your maximum heart rate. 

So that same 50-year-old would want to keep their intensity to around 119 beats per minute while exercising to burn fat. 

Similar to maxiumum heart rate, fat-burning heart rate decreases with age. 

So while an 18-year-old would need to stay around 140 beats per minute, a 75-year-old would only need to get up to 101 beats per minute. 

However, certain medications can increase or lower your heart rate. Beta blockers, for instance, lower heart rate by blocking the effects of hormones like adrenaline. 

These are typically prescribed for unexplained tachycardia - resting heart rate over 100 BPM - and high blood pressure.

Additionally, some antibiotics, corticosteroids, and over-the-counter decongestants can increase your heart rate.

In order to avoid stressing the heart too much, it's crucial to consult a doctor about the ideal heart rate to aim for if you are on one of these medications.  

If you want to make sure you're staying in the fat-burning zone, there are several ways to track your heart rate. 

The traditional method involves using your fingers to track your pulse on your neck, wrist, or chest. 

However, wrist monitors like the Apple Watch are much more common and can keep track of heart rate throughout an entire workout and during rest. 

According to the federal Physical Activity Guidelines for Americans, adults need about 150 minutes of moderate physical activity every week or 75 minutes of vigorous exercise. 

The Department of Health and Human Services also suggests US adults get at least two days of muscle-strengthening exercise, such as weightlifting, every week.