All the time, I hear fitness professionals tell their clients not to exercise above a certain heart rate, as if it were bad for people to run or bike fast. Target heart rate has become a buzz phrase, with many cardio machines display a “fat-burning zone” on their panels, encouraging people to exercise in a specific heart rate range. Have you ever wondered if your clients really have to exercise in a specific heart rate zone to lose fat? And what happens if they venture out of that zone?

Understanding the best way to burn fat starts with some basic facts about how your body gets its energy: 

The body primarily uses fat and carbs for fuel. A small amount of protein is used during exercise, but it's mainly used to repair the muscles after exercise. 

The ratio of these fuels will shift depending on the activity you're doing. 

For higher intensity exercise, such as fast-paced running, the body will rely more on carbs for fuel than fat. That's because the metabolic pathways available to break down carbs for energy are more efficient than the pathways available for fat breakdown. 

For long, slower exercise, fat is used more for energy than carbs. 

When it comes to weight loss, it doesn't matter what type of fuel you use. What matters is how many calories you burn as opposed to how many calories you take in.

This is a very simplified look at energy with a solid take-home message. When it comes to weight loss, what matters is burning more calories, not necessarily using more fat for energy.

It may seem like a no-brainer that regular exercise can help you burn fat and lose weight. But, it's not just about the calories you're burning, it is also about the adaptations your body makes when you exercise on a regular basis. Many of those adaptations lead directly to your ability to burn more fat without even trying. When you exercise regularly, your body becomes more efficient at delivering and extracting oxygen -- Simply put, this helps your cells burn fat more efficiently; it also delivers  better circulation which allows the fatty acids to move more efficiently through the blood and into the muscle. That means fat is more readily available for fueling the body.

Adding more muscle by lifting weights can also help with burning fat, especially if you're also dieting.  Lifting weights keeps your metabolism going and helps you burn extra calories -- If you lift weights at a higher intensity, you can actually increase the calories you burn after your workout.

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