I often get questions from clients that seem appropriate to share and answer to our wider community of fitness enthusiasts. One that frequently arises pertains to low- versus high-intensity workouts. I’ve answered it below.
(Got your own question about fitness, fat loss or cardio training? Email me at email@example.com, and I’ll cover it in a future blog.)
QUESTION: Why do I burn more fat when I work out at a higher intensity than at a lower intensity?
ANSWER: So, this is how fat burning works: You burn a higher percentage of fat at lower intensities (with the largest percentage loss attained at the lowest intensities); however, you burn more total fat at higher intensities. The reason is chemical: At a lower heart rate the body burns glycogen (the storage form of glucose and carbohydrates in animals and humans); while at higher heart rates the body burns not just glycogen, but also carbohydrates found throughout our musculo-skeletal structure.
Let me illustrate with an example:
Let’s say you perform a low-intensity workout for 45 minutes on a TRUE ES900 Recumbent Bike and burn 300 calories. Roughly 80% of those burned calories are from fat, i.e., a loss of 240 fat-calories. Now, suppose you do a high-intensity workout for 10 minutes on a Cybex Arc Trainer and burn 800 calories. Even if you burn only about 60% of these calories from fat, your total fat-calorie loss is 480.
In my opinion, backed by research, if your exercising goal is weight loss, you should always aim for the workout that burns the most calories —unless you’re trying an energy titration system for an Olympic performance! You can achieve your weight loss goal by walking for 2 hours (low intensity) or running for 45 minutes (high intensity).
Of course, results vary with the type and duration of exercise, and your own satisfaction with a routine plays a major role; you’re much more likely to stick with a workout that you enjoy rather than one that feels like work. That said, whether you’re hitting the gym or have a fitness studio in-home, a 30-45 minute cross trainer (on the Arc or other elliptical) workout would be more effective than an hour of spinning, let’s say—but if you love spinning and shy away from ellipticals then, by all means, stick with what you love!