What Is HIIT, and How Often Should I Do HIIT Workouts?

HIIT is an acronym that stands for high-intensity interval training. The concept of HIIT is to perform an exercise all out (or as close as possible) for a short period of time followed by a shorter period of rest. For example, performing box jumps for 40 seconds followed by 20 seconds of rest. Because you're working at an intense level, most HIIT workouts [4] usually take no longer than 30 minutes to complete.

If your goal is to lose weight, burn fat, and build muscle [5], you should consider adding HIIT into your workout routine. HIIT "gives you a hormonal response that's conducive to muscle growth, and it's more anabolic — where you're developing tissue, muscles, collagen, cartilage, things of that nature," Rondel King, MS, CSCS, an exercise physiologist at NYU Langone's Sports Performance Centre [6], told POPSUGAR in a previous interview [7]. Because HIIT workouts are done above your anabolic threshold, they elicit a hormonal response (growth hormone and testosterone) that can lead to muscle growth, Rondel explained in a previous interview [8].

To reap the benefits of HIIT workouts, aim to do them two to three times a week, Rondel said. He also recommends doing two to three days of strength training a week to help you build muscle and burn fat. If you like cardio, Rondel said you can do up to three to four days of cardio a week as long as the sessions are no longer than 30 minutes since cardio can be catabolic to muscle growth [9].

How Long Does It Take to See Results From HIIT?

If you're thinking, "Wow, the benefits of HIIT sounds amazing and I need to start ASAP," but also wondering, "How long will it take to see results from HIIT?," there isn't an exact answer. "It comes down to the individual . . . you can lose one to two pounds of adipose tissue within a week," Rondel explained. If you're less conditioned, you may initially lose more than one pound a week.

How Sleep and Stress Play a Role in Fat Loss and Building Muscle

You've got to put in work at the gym and make healthier nutritional decisions to see results, but don't forget about getting enough sleep and manageing your stress. "Being in a high-stress environment is generally not good, especially long term," Jason Machowsky, RD, CSCS, a board-certified sports dietitian and exercise physiologist at the Hospital For Special Surgery's Tish Sports Performance Centre [10], told POPSUGAR.

According to Jason, being in high-stress environments for a prolonged period of time can cause your cortisol levels to increase, which can potentially lead to weight gain [11]. "Typically, when people are stressed, they might tend to eat worse, they make poor decisions, they skip meals, or they don't exercise," Jason said. The same can happen when you're sleep deprived, he explained.

As you sleep, your body recovers from exercise and produces growth hormone. If you aren't getting enough sleep, your growth hormone production will decrease, which can result in the loss of muscle mass, Rizwana Sultana [12], MD, assistant professor of pulmonary critical care and sleep medicine at the University of Texas Medical Branch, said in a previous interview [13]. Your workouts are important, and so is your recovery!

If you're ready to start seeing results with HIIT, make sure you're doing HIIT two to three times a week, getting enough sleep, and eating foods that will fuel you all day long. To get started on the right foot, check out some of our favourite HIIT workouts:

• A 25-minute cardio and strength HIIT workout [14]
• A 25-minute abs and legs HIIT workout [15]
• A 30-minute equipment-free HIIT workout [16]
• An advanced 30-minute HIIT workout [17]