Q: I’ve heard it brought up a few times by others recently, and I remember from your old daily training blog that you guys sometimes use interval cardio to burn more fat. What is that and how should I use it?
A: There are surprising facts about using interval cardio to burn more fat, but before we get to those, let’s explain interval cardio on a running track. To do interval training, you sprint the straightaways all out and walk the curves. Another good example is running stairs—you run up for intensity and coast down. In other words, you alternate high-intensity bursts with lower-intensity activity.
Studies show that interval cardio burns more bodyfat than steady-state aerobics by boosting the metabolism long after the session is over. That’s primarily because of muscle damage—the high-intensity intervals are a lot like weight training in that they stress and damage fast-twitch muscle fibers in the quads, calves, and hamstrings.
Your metabolism is higher afterward because your body has to repair the muscle damage, just like from a weight workout, and it uses bodyfat for the energy to accomplish that. Plus, the low-intensity walks between high-intensity intervals help you burn bodyfat as well, especially toward the end of the session when the bursts have depleted all circulating sugar from your bloodstream. That’s when bodyfat becomes the primary energy substrate (you’ll see how to take advantage of that for even better fat burning in a moment).
The problem with interval cardio is muscle damage—it’s like a hard leg workout. That means you shouldn’t use it the day of or the days around your leg workout or excessive damage may occur. When using interval cardio to burn more fat, we generally try to do it on a day that’s as far from our leg day as possible.
Jonathan used to use an exercise bike, pedaling all out for 30 to 40 seconds alternated with a slow pace for about a minute to a minute and a half. His interval cardio workouts last about 20 minutes on average. He’ll also sometimes opt for a treadmill but will use the steepest incline combined with a higher speed (but not fast enough to run).
Steve, on the other hand, prefers to run. He sprints for 50 to 100 yards and then walks for about two minutes. His interval cardio workouts last about 30 minutes, as he uses a longer walk as a cool down (and to get the extra fat burn we mentioned earlier). We both use a few steady-state cardio sessions during the week, usually 20-30 minutes each on an exercise bike or treadmill just to add to the calorie deficit after a weight workout (every little bit helps).
One warning regarding steady-state cardio: Steve learned that it can reduce his leg size when using a medium-hard cadence for distance. At the beginning of one of our ripping phases, he was doing long runs, and his pace was fairly slow due to being deconditioned for cardio. That made the activity primarily slow-twitch dominant; however, as he regained his aerobic abilities, his running pace began to increase—and his quad size began to decrease. Here’s why…
When you run at a medium-fast pace, you bring in the type 2A fast-twitch fibers in a high-endurance capacity. Those fibers have both aerobic and anaerobic capabilities and are the fibers most prevalent in big bodybuilders. If you do too much medium-fast cardio, however, it’s like doing very high-rep weight work—the muscles get stringy and lose size because the 2As become more aerobic dominant. They are essentially morphing into fibers resembling slow-twitch without much size. While the 2As still have anaerobic capability, it’s being downregulated due to the medium-fast cardio sessions. (That effect is much less prevalent in drug-using bodybuilders.)
If you want your legs to stay muscular—like Jonathan’s in the photo below—either walk/slow jog or do interval work. Do NOT do medium-fast runs for distance or your 2As could become too aerobic and lose size and anaerobic ability.
NOTE: For more on optimal cardio, as well as our ripping diets, workouts, tips, and tricks, see the X-treme Lean e-book, also available with other fat-loss, muscle-on e-books in the money-saving Triple-Shred Combo Offer.)
Till next time, train hard—and smart—for BIG results.
—Steve Holman and Jonathan Lawson
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