If you're the type of person who frequently checks your heart rate during exercise to ensure you're in the fat-burning zone, you should stop. In reality, there's no specific fat-burning zone that's the key to achieving a beautiful, balanced body.
1. How effective are exercise and weight loss?
1.1 A burning issue
This has always been a concern for those who want to lose weight. If we look at the gym's wall charts or cardio equipment or listen to many personal trainers, we will understand the “fat-burning zone”. The standard advice for engaging in this zone is to exercise at about 60% of the body's maximum heart rate. That level of exertion is relatively low intensity; most people can speak complete sentences while exercising through the speaking test. It is said that working in this zone will burn more fat and lead to more lasting weight loss than doing the same exercise at a higher intensity.
Our bodies primarily use a combination of stored fat and carbohydrates for energy. The less active a person is at a given time, the greater the proportion of that fuel mix comes from fat. As exercise intensity increases, the contribution of carbohydrates to energy expenditure also increases.
At rest, fat makes up 85% of the calories burned. This proportion decreases to about 70% during light exercise. During moderate jogging, the mix shifts to approximately 50% fat and 50% carbohydrates, shifting more toward carbohydrates as we run faster. So it is true that at some exercise intensities, our bodies will burn a higher proportion of fat than at others.
But that doesn't mean this biological process is the key to weight loss through exercise. Experts explain that those who subscribe to the 'fat-burning zone' theory often overlook the most critical factor in weight loss: caloric intake.
1.2 Dispelling the Fat-Burning Zone Myth
First, while burning a higher proportion of fat during exercise might seem advantageous for weight loss, the impact of exercise intensity on body composition is negligible.
Christopher Breen, a physiologist and online coach in Long Island, explains, "The idea that, once you hit this zone, fat is magically sucked out of your system is simplistic. It completely ignores the fact that weight loss or maintenance is fundamentally a matter of calories in versus calories out."
If maximizing the percentage of fat burned were the primary determinant of weight loss, then remaining sedentary would be optimal, as that's when we burn the highest proportion of fat relative to carbohydrates. However, as Breen points out, the total number of calories burned is what matters, and this leads to the second major issue with the fat-burning zone concept. Christine Brooks, an adjunct lecturer at the University of Florida and the exercise science coordinator for USA Track & Field explains, "If you're exercising at a lower intensity, you're burning fewer calories per minute. A typical person walking for an hour burns only a few hundred calories. In the same amount of time, you could burn twice as many calories running, cycling, or using an elliptical at a moderate intensity.
Let's return to reality: when we schedule workouts, we typically think about time, not calories burned. Therefore, in many cases, even if we exercise 30 or 45 minutes before or after work, we won't burn as many calories if we spend that time in the fat-burning heart rate zone. Brooks states, "I'm always encouraging people to be more aggressive with their workouts, rather than believing in the myth of frequent, low-intensity exercise for creating a greater calorie deficit”.
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