Q: Does the 'fat-burning zone' really exist?
A: If you’ve ever hopped on a piece of cardio equipment intent on getting in a great workout, you’ve likely seen it - the colorful graph covered with numbers correlating heart rate with fat burning. The sweet spot as indicated on the graph is a zone referred to as the 'fat-burning zone'. This leads cardio-enthusiasts to think they need to taper back on intensity and work out solely in the highlighted area to burn the most fat. Backers of high-intensity interval training, however, prefer to perform extremely intense intervals ignoring the heart rate guidelines altogether. Should the heart rate chart and fat-burning zone really dictate your overall effort?
The body does rely on different substrates during exercise according to the exercise intensity. At a lower intensity level, the body relies more on fat as a fuel source as it more time to breakdown fat and convert it to energy (a longer process). During high intensity efforts, the body begins to metabolize carbohydrates instead, preferring their speed of breakdown to fuel higher levels of exertion. This fuel preference is also dictated by the availability of oxygen which is required for fat utilization.
The preference for fat at lower levels of intensity has created the fat-burning zone - an intensity at which the highest percentage of calories burned are coming from fat. While the lower intensity exercise may burn more fat, following the chart verbatim shouldn’t be the main focus of your workout program. For one, the heart rate levels are going to be different for every individual. Second, it’s likely not worth the mental energy to run your entire program off the chart estimates. According to JC Deen, head trainer at JCDFitness.com, “I think it's a general waste of mental energy to worry about it. The fat-burning zone may exist, but I wouldn't worry about hitting that zone if the goal is fat loss specifically.” Instead, he advises clients to focus the majority of their efforts on generating a calorie deficit. “You may burn a little more fat during exercise, but if a calorie deficit isn't present, then it will all even out in the end you won't lose much fat at all.” In lower intensity programs, the overall calorie burn during a workout will be lower than a high intensity workout - regardless of whether those calories come from fat or carbohydrates.
Monitoring exercise intensities can certainly provide cardio-enthusiasts with a way to maximize potential. Although steady-state cardio at lower intensities may not necessarily lead to higher levels of fat loss, it can provide a much-needed break from higher intensity workouts. Deen agrees that lower intensity cardio deserves a spot in most workout programs. “I think steady state cardio is useful when aiming to create a caloric deficit because it offers an opportunity to burn more calories without increasing intensity, and delaying recovery from heavy weight training workouts.” Incorporate lower intensity cardio following hard days to improve circulation while encouraging recovery or during deload weeks when exercise intensity should naturally decrease. Rather than stressing over exact values based off of a chart, gauge intensity based on your current perceived exertion and cycle higher and lower intensity efforts for maximum results.