Workout Routines

Everything You Need to Know About HIIT

Maximize your fat-burning efficiency with high-intensity interval training.


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Food, Fuel & Fat

Research exists on the effectiveness of training with an empty stomach, but this comes with some caveats for HIIT. “A study from Northumbria University [in England] showed that people can burn up to 20% more body fat by exercising in the morning on an empty stomach,” Grinnell points out. “However, I don’t think it’s optimal if you’re trying to preserve or build muscle tissue while burning body fat. To enhance the fat-burning and muscle-building effects of HIIT, consume 10 grams of BCAAs or 30–50 grams of whey protein 30–90 minutes before.”

This, Grinnell says, will play into HIIT’s most cherished payoff— muscle preservation while still allowing you to dig into stored fat. But at all times, even in the presence of branched-chain amino acids, you’ll want to be properly fueled for the work ahead, which may mean starting your prep well in advance.

“The day before a HIIT or sprinting workout, it would also be wise to have a higher-carb day to store extra glycogen for more intense work,” says Grinnell. “This is particularly important if you’re combining a sprint workout with weightlifting.”

Bottom Line

Go early—but don’t go empty. HIIT cardio before your first meal of the day can help you to burn more fat, but make sure you take 10 grams of BCAA s or 30–50 grams of whey 30–90 minutes before training.

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Supplement Upgrade

If you’re dedicated to high-intensity interval training, then you’re all about performance. So it makes sense to power up with proper supplements—those that go beyond your typical fat burner—to fuel that performance. If you’re in the middle of a 20-second sprint and you hit the wall 10 seconds in, you’re depriving yourself of those extra few seconds in high gear. Luckily, there’s a supp for that.

“There’s no doubt that proper supplementation can help any type of exercise, but especially HIIT,” says Grinnell. “When working out at a high intensity, it can be hard to sustain an intense output for long. Beta-alanine has been shown to enhance muscular endurance. Many people report being able to perform one or two additional reps in the gym when training in sets of 8–15 reps. It can also improve moderate to high-intensity cardiovascular exercise performance, like rowing and sprinting, and offer protection from exercise-induced lactic acid production.”

But that’s not the only useful supplement. “Creatine improves power output and is often used by athletes to increase high-intensity exercise capacity and lean body mass,” Grinnell says. “Beta-alanine and creatine are must-haves for interval trainers— but the latter may be more vital.

“Creatine is also helpful for replenishing the phosphagen, or ATP/CP, system during intense exercise,” Grinnell adds. “So if you’re feeling fatigued during a sprint workout, supplementing creatine can help you keep your pace high. If the phosphagen system gets enough creatine in it, you have a better chance of sustaining max exertion during sprints and recovering properly between them.”

Bottom Line

Taking three to five grams of creatine and two to three grams of beta-alanine 30–60 minutes before and immediately after sprint workouts will help you sprint faster for more total sprints in a given session.

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