Here’s What Happens to Your Body During and After a HIIT Workout

Some people swear by HIIT workouts. Others wonder what they even are. In short, HIIT stands for high-intensity interval training, which involves a short workout and quick bursts of energy with quick resting periods. (Most HIIT workouts are not more than 30 minutes.) Trainers recommend these types of workouts because they burn serious energy, which helps you burn more fat and calories. Plus, the body keeps burning energy long after the workout. Here’s why that is, and what happens to your body during and after one of these speedy, intense workouts.

Women exercising

HIIT workouts have some serious benefits for your body. | Bojan89/iStock/Getty Images

When you give 100%, your body goes into overdrive

HIIT workouts should be done by giving 100% effort for 15 to 30 seconds. This is the optimal amount of time for an anaerobic workout (your body is “deprived” of free oxygen) before a 60-second rest period. According to Men’s Health, doing any less might mean you won’t see the results you want, and doing any more is too much on your body.

When your body works anaerobically, it produces lactic acid because you can’t get enough oxygen to your muscles to keep them working properly. Basically, your body supplements that oxygen with the lactic acid. When lactic acid is produced, adrenaline comes with it, which helps move fat throughout your body and creates that fat burn and muscle buildup you’re looking for.

After the HIIT workout, the body enters a rebuilding mode

When you deprive your body of oxygen, it needs to rebuild itself to get those oxygen levels back to normal. You’ll be very out of breath after HIIT because your body is trying to grab as much oxygen as it can to return to homeostasis.

After about a half hour, you might notice you’re pretty hungry. That’s because your body needs to replace glycogen fuel stores, too, so it tells you it needs food to help out with that. You’ll want to grab something with complex carbohydrates, such as whole wheat pasta or whole wheat bread, to refuel.

Hours after the HIIT is done, your body is still burning fat because your metabolism is on a roll trying to replace nutrients that were lost during the HIIT workout, such as carbohydrates and electrolytes. Your insulin sensitivity is at its best, so your body won’t store glycogen as fat. The effects of a HIIT workout can impact your body up to 48 hours after the workout.

Working your body in intervals burns more fat in the long run

If you jog at a steady pace, you’ll do your body good but definitely aren’t giving 100% effort. This means your body doesn’t have to work as hard to repair and rebuild its oxygen levels. A jog is a great form of cardio, but it requires a much shorter recovery time than HIIT. This means your body won’t feel its effects for as long, and you ultimately won’t burn as much fat from a jog as you would from a HIIT. Not only are HIITs a great time saver, they’re one of the best things you can do for your body.

Does HIIT work?

HIIT definitely has some great benefits, especially if you don’t have a lot of time to dedicate to working out. Spending 30 minutes on a HIIT workout will essentially be just as beneficial for your body as spending an hour or more at the gym (assuming you’re jogging or doing an exercise that doesn’t require 100% effort.) However, it’s important to know what your body can handle before implementing HIIT workouts into your routine. People sometimes think a 30-minute workout is no big deal even if they’re not in shape; actually, these 30-minute workouts are extremely intense. If your body can’t handle it, you risk injuring yourself. Make sure you to always listen to your body and know if you’re pushing yourself past the breaking point.

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