High-intensity interval training (HIIT), where you work as hard as you can for short bouts, followed by a short rest period, is one of the most popular training modalities, and rightfully so. HIIT is time efficient, it can be modified for all levels, it can improve your overall athletic performance and health, and, when done correctly, it can help you build muscle.
Does HIIT Build Muscle?
"Yes, it can. There are certainly certain types of HIIT workouts that are better than others for building muscle, but in general, they can," Aaron Karp, MS, ATC, CSCS, an exercise physiologist at the Hospital For Special Surgery's Tisch Sports Performance Center, told POPSUGAR. In order to build muscle, your HIIT workouts should focus on strength training as opposed to just doing calisthenics, such as jumping jacks, Karp explained.
There's nothing wrong with incorporating aerobic exercises into your HIIT workouts, but Karp recommends pairing them with strengthening exercises to get stronger and build muscle. Moves such as squats, lunges, and single-leg deadlifts "in a series will lead to muscle fatigue, and at the end of the day, that's how you build muscle," he said. Adding strength exercises to your HIIT workouts will make your cardiovascular system and muscles fatigue, which helps you build strength, he added.
How to Program Your HIIT Workouts to Build Muscle
According to Karp, the most important variable to focus on is your work-to-rest ratio. "As far as specific numbers, it's really what you're able to do," he explained. If people are unconditioned or new to training, Karp typically advises them to begin with a 1:2 or 1:1 work-to-rest ratio. For example, performing each exercise for 20 seconds, followed 40 seconds of rest, or performing each exercise for 20 seconds, followed by 20 seconds of rest.
If you're more advanced or once you become more conditioned, Karp recommends advancing to a 1:1, 2:1, or 3:1 work-to-rest ratio. "I wouldn't really go much above 5:1 if you're talking about specifically building strength," he said. This is because most people won't be able to sustain working at that level of intensity, and "you're going to be limiting how much you can actually challenge your muscles," he said. Additionally, Karp said your rest shouldn't be too long, taking no more than 30 to 60 seconds in between each exercise (depending on your level), and one to three minutes of rest in between each circuit/round.
In addition to focusing on your work-to-rest ratio, Karp said it's imperative to have compound exercises, which are multijoint movements that work large groups of muscle at once, in your routine as opposed to isolated movements such as bicep curls. You don't have to cut movements like curls completely, but, "You want to primarily be doing compound movements," Karp said. If you want to keep isolated movements like curls in your workouts, he recommends programming them in a way that allows you to do them to slightly rest without taking a full break.
You don't need to use weights to build muscle with HIIT workouts, and if you do, Karp said to make sure you aren't just opting for the heaviest weight possible, but that you instead use a weight that will challenge you while maintaining proper form. You can also manipulate the amount of time under tension, how long your muscles are under strain, by adjusting how long you perform each exercise to improve your strength levels without using heavy weights. "You don't need to actually use as much weight because you're affecting other variables, the time-under-tension variable . . . That's really the advantage of HIIT," he said.
You can opt for total-body HIIT workouts or you can focus on one body part, such as your legs. "You can do it where you're hammering one muscle all the way out — that's probably going to be the thing that's going to lead to the most muscular fatigue," Karp explained. For example, doing a goblet squat, a lunge, and a squat jump.
Another option Karp recommends for those who do a lot of cardio and are transitioning to more strength training is to work alternating muscle groups during the workouts. For example, performing 10 squats, 10 overhead presses, 10 lunges, and then 10 push-ups. "You're constantly working and one muscle is resting while the other muscle is working." He explained that you won't get as much of a strength benefit when following this format, "but it is going to tax your cardiovascular system more because your heart has to pump blood to different places."
How Long Does It Take to See Results With HIIT?
Now that you know you can build muscle with HIIT and have a general idea as to how to program your workouts, you may be wondering how often you should do HIIT workouts and how long it will take to see results. According to Karp, it will take a minimum (emphasis on minimum) of four to six weeks to start seeing results. Someone who is unconditioned may experience neurological changes within the first two weeks, "meaning your body is not going to look any different, but the exercises feel better or you feel like you're more coordinated," Karp said.
As far as physical changes, such as the size of your muscles or how much body fat you have, it will take a minimum of four to six weeks and sometimes closer to six to eight weeks, Karp explained. Though, how long it will take to see results varies from person to person based on variables such as genetics and your fitness level.
How often you should do HIIT workouts also varies based on your fitness ability, but Karp advises doing HIIT workouts on nonconsecutive days. "You can't just do one [HIIT workout] a week. That won't be enough. Two is better, three is ideal," Karp said. If you're doing more than three workouts a week, Karp said to be careful, because your body needs time to recover. "Your recovery is when you actually get stronger, so if you're not giving your body that time, you're either not working hard enough during your workout or you're going to end up getting injured down the road," he said.
We know this is a lot of information to digest, but we at POPSUGAR and Karp recommend working with a qualified professional to create a training program that addresses your goals and specific needs, and to fill in the gaps on the days you aren't doing HIIT workouts.