You want great fitness results and you want them fast. That’s why, nowadays, fitness is all about high-intensity interval training (HIIT)—burpees, bootcamps, and Tabatas pushing us to the edge of death, followed by a protein shake. Plenty of studies even show that anaerobic exercise like HIIT burns more fat than traditional aerobic cardio such as a 30-minute jog.
So why am I committing fitness heresy by telling you to do more aerobic exercise and less anaerobic exercise? Because even though all that high-intensity insanity is valuable for getting in a solid workout fast, and for pushing you to your limits, there are downsides—especially if it's your only mode of exercise. Anaerobic exercise—when your heart rate stays in the upper limits (generally 150 beats per minute or higher) for prolonged periods—is stressful. Literally, in a lizard-brain way: It generates higher emotional responses and fight-or-flight activity. And given that we’re already stressed by daily life, adding more stress via those flailing kipping pull-ups isn't helping matters. (Aerobic exercise, on the other hand, reduces stress.) What's more, turning on your fight-or-flight nervous system often increases your inflammation, which is linked to all kinds of health problems. (The truth, as you can see, is more complex than what’s on the Orangetheory website.)
If you're just in the game to burn fat, you should know that you'll shed most of it during aerobic exercise—and also, working out isn't really how you lose fat anyway. Eating less (and, ideally, better) is the one true path to that sweet D'Angelo V-muscle. And if you're cutting calories for a decent amount of time, you should be moderating your physical stress, since you’re also depriving your body of energy.
Which brings us to why you need more cardio. When you train aerobically—sustaining a heart rate between 120 and 150 beats per minute for most guys—a few advantageous things happen:
1. Your heart gets swole.
But, you know, in a good way. Your heart can pump more blood per beat, so it works less for the same output.
2. Even your cells get swole.
Cardio strengthens mitochondria, the so-called “power plants” of your cells. The more efficient they are, the more fuel your muscles have to work with.
3. Your muscles don't get swole. But they do build more blood capillaries.
With better blood flow, your muscles can absorb more oxygen and clear more waste.
4. Darn near everything in your body gets better, faster, or smarter.
You recover better, because aerobic exercise refuels you and clears lactic acid from muscles. Also, aerobic exercise actually makes you better at HIIT. After you do a few quick sprints, your aerobic system drives most of your performance anyway; by doing more aerobic training, you’ll actually boost your overall conditioning and recovery regardless of how hard the exercise. Aerobic fitness is way better for your brain, too.
Now, I’m not saying you should foreswear CrossFit and cancel your box membership. Anaerobic, high-intensity-interval-type exercises won't destroy you. Nor am I saying you should become a cardio bunny who strolls on a treadmill for 60 minutes every morning while watching Michael Strahan's gap-toothed smile on a flatscreen.
Here’s what I am saying: If you do HIIT and nothing else, take your frequency down a notch—maybe even take a full month off—and do light aerobic work two to three times per week. (You can still lift weights.) Try an easy circuit of bodyweight exercises, go for a light jog in the park, or make your sports training aerobic—if you play soccer, for example, do 30-minute soccer drills in that 120 to 150 bpm sweet spot. Within just a couple weeks, you'll likely notice an improvement in your conditioning, in your sleep, and in your post-workout mood—because you haven't spent the last hour lying in a fetal position after doing 100 straight burpees at the gym.