Answers to Commonly Asked Questions About HIIT Workouts

Whether you’re looking for a time-efficient workout or just looking to shake up your routine, chances are you’ve encountered the exercise practice known as HIIT (AKA high-intensity interval training). The concept is simple enough: short, high-intensity activity periods, followed by brief periods of low-intensity activity or rest. Several of these intervals, stacked back to back, form the workout method known as HIIT. With so many enticing characteristics, it’s no wonder HIIT workouts are utilized by at-home gym goers and personal trainers alike!

What is HIIT?

To fully understand why HIIT is such a delicate balancing act, it’s useful to learn what HIIT is and how it impacts your body. HIIT is an exercise practice that couples maximum-effort activity with periods of idleness or low-intensity activity. The idea is to shock your body by pushing your muscles to the point of fatigue, then to back off and allow recovery time.

When done right, this formula pays off, since HIIT workouts are proven to slightly increase calorie expenditure as shown in a 2016 study¹ comparing the physiological changes during HIIT versus sprint interval training¹. HIIT workouts accelerate your heart rate and boost your body’s ability to accommodate increased oxygen flow.²

How often should I be doing HIIT workouts?

If HIIT sounds like a compelling workout, you wouldn’t be wrong. However, like anything that’s high intensity, HIIT workouts can take a toll on your body and mind if overdone or not done properly.

Like so many things in fitness, it depends on the individual. For all exercisers, experts from Les Mills suggest engaging in no more than 30–40 minutes of HIIT training per week³ (with your heart rate above 90%). Half of that total time will be spent on high-intensity activity with rest periods mixed in. To keep overtraining at bay, ample rest between each workout is a must. This means you need to factor in rest days to keep your body going strong.

If you’re wondering whether or not you’re investing enough effort in your intervals, keep in mind that you should feel like you’re at a 9-10 on the RPE scale during each interval, with 10 being maximum effort.

Why do people love HIIT workouts?

This might seem obvious, but most people love a workout that’s time efficient. Those with busy schedules who don’t have time to squeeze in an hour-long running session every day can often create the time to accomplish a 15-minute HIIT workout.

In addition to being time-efficient, HIIT workouts are helpful for those who don’t have a dedicated home gym or own at-home fitness equipment. The fact that HIIT workouts can be done without equipment makes them one of the most versatile forms of exercise.

Lastly, HIIT classes allow you to engage in exercises that you likely couldn’t do continuously for 10 or 15 minutes, like sprinting, by breaking them down into intervals. These brief but intense intervals can offer the opportunity to build your endurance and strength in bite-size sessions, which may feel more sustainable to some exercisers. As previously mentioned, HIIT can increase calorie expenditure and improve oxygen consumption. Over time, you can improve your general fitness with regular HIIT workouts.

Is there such a thing as doing too many HIIT workouts?

Just as you’re more likely to make a mistake when you’re working on no sleep, you’re more likely to suffer an injury when teetering on the brink of exhaustion. When you don’t give your muscle tissue enough time to repair and grow, you increase your risk of pulls, sprains, or tears.

For this reason, it’s wise not to overindulge in HIIT. As mentioned before, the effectiveness of HIIT workouts primarily relies on you giving maximal effort to each and every interval, coupled with adequate rest.

Don’t rule out the effects of mental fatigue, either. When you work out at a high-intensity level, your body releases stress hormones like cortisol. On one hand, cortisol⁴ can boost your energy, fight inflammation, and more. On the other, too much cortisol can disrupt your mood, induce fatigue, and cause headaches to arise. HIIT workouts, while great in moderation, should be kept to a few sessions a week (as noted above) to allow your cortisol levels to balance out as you rest.

What should you do on days when you don’t do HIIT workouts?

If you’re looking to round out a HIIT exercise regimen with a roster of other exercises, try mellowing out with a low-impact routine, such as resistance training, aerobics, or stretching. Yoga and Pilates are both great ways to expel extra energy while keeping things relatively low-key. Steady-state cardio, such as rowing or walking on the treadmill at a consistent pace, can be used as alternatives to energy-depleting HIIT circuits.

Since HIIT is often cardio-based, some trainers are proponents of making off-days strength or resistance-training days. Consider adding strength workouts to your weekly routine to help build muscle and strength. Incorporating strength workouts will help bring balance to your general fitness level, so you aren’t solely building cardiovascular endurance from your HIIT workouts.

How do you get the most effective HIIT workout?

When you’re beginning a HIIT workout regimen, make sure your body is prepared for high intensity. If you’re making your first foray into fitness—or the first one in a while—ease into HIIT by starting with a few weeks of cardio and weight training sessions. With a progressive game plan in motion, you can start dropping in HIIT exercises once a week. Not only will building a fitness foundation stave off injury, but it will ensure that you can tackle more than an interval or two.

Another snippet of workout wisdom would be to switch up your HIIT exercises so you don’t hit a fitness plateau.⁵ Cycling through the same five exercises might make for an easy, no-think workout that you can put on repeat. Unfortunately, it likely will not provide your body with the challenge to reap continual total-body gains. To vary your routine, consider incorporating machines like a treadmill, bike, rower, or elliptical. Alternatively, put the gym (or home gym) on hold for a day and jump in a pool or run outside to shake things up.

What are the best HIIT exercises?

Although strength exercises can most definitely be incorporated into a HIIT format, cardio exercises tend to pair better with HIIT’s short circuits. Regardless of which types of exercises are integrated, always make sure to use proper form and technique in order to minimize the chance of injury and maximize results.

By-the-book cardio exercises like tuck-ups, flutter kicks, burpees, and lunges are always fair game for a HIIT workout, but they’re by no means your only choice. If you’re averse to counting based on reps, consider sprinting on a treadmill, cycling on a stationary bike, or freestyle swimming in a pool. Treadmill sprints are actually one of the most common ways to execute a HIIT workout, but if you don’t have a treadmill, visit your local park and try sprinting on the grass or a path.

Can’t shake the desire to incorporate some strength training? If you do want to turn a HIIT session into a muscle-maker, then grab a weight, kettlebell, resistance bands, or even a medicine ball. Unlike a dumbbell, medicine balls allow you to manipulate them explosively (i.e. medicine ball slams) for the most textbook-like HIIT workout.

How long should a HIIT workout take?

While it’s possible to get incredibly technical, it ultimately distills down to this tried-and-true truth: If you’re noticing a dropoff in your performance, chances are it’s time to take a break. When it comes to exercises like running, biking, swimming, or rowing, HIIT can dramatically improve your performance and form. However, the stipulation is that you must maintain good form throughout every interval. If your form has become less than top-notch, shift into recovery workout mode and pick it up again in a day or two.

For most—especially fitness first-timers—a decline in performance can happen somewhere around the 30-minute mark. As you ramp up your practice, you’ll likely be able to push into the 45-minute mark, but most professionals warn against stretching into 60 minutes or beyond unless you’re a training athlete.

How long should you rest between HIIT intervals?

Those who desire a more moderate workout may want to adopt a 1:2 ratio. For example, training at a maximum of 60 seconds and then resting for double the amount of time. Other options include a 1:1 ratio, 1:3 ratio, or even a 2:1 ratio, such as Tabata training. Once you have a baseline that you feel comfortable with, you can easily improvise from there.

It’s worth keeping in mind that shorter work periods don’t necessarily mean the intervals are easier. Shorter work intervals allow you to maintain a higher intensity, primarily because you don’t have to maintain the work period for as long. You want to sustain the highest level of effort possible in order to make HIIT exercises worthwhile.

Get started with iFIT HIIT workouts

Ready to commit to trying HIIT? Remember to take it slow. You can build on HIIT intervals; there’s no pressure to knock out a 20-minute workout right away. Browse a series of curated HIIT workouts and discover one that’s just right for your gameplan, whether you’re a beginner or an athlete in training.

Those who want to dig deeper into HIIT training can learn more about Tabata workouts, a subcategory of HIIT that focuses on ultra-short intervals and rest periods. No matter your goals or skill level, jump in and give it a go. It’s all about pace, not winning the race!

References

1. Wood, K. M., Olive, B., LaValle, K., Thompson, H., Greer, K., & Astorino, T. A. (2016). Dissimilar Physiological and Perceptual Responses Between Sprint Interval Training and High-Intensity Interval Training. Journal of Strength and Conditioning Research. https://doi.org/10.1519/JSC.0000000000001042. 

2. Wood, K. M., Olive, B., LaValle, K., Thompson, H., Greer, K., & Astorino, T. A. (2016). Dissimilar Physiological and Perceptual Responses Between Sprint Interval Training and High-Intensity Interval Training. Journal of Strength and Conditioning Research. https://doi.org/10.1519/JSC.0000000000001042. 

3.Hogan, E. (2021, March 22). New study reveals the optimum weekly dose of HIIT. Les Mills. https://www.lesmills.com/us/fit-planet/fitness/how-much-hiit/.

4. WebMD. (n.d.). What is cortisol? WebMD. https://www.webmd.com/a-to-z-guides/what-is-cortisol. 

5. Sweat. (2019, August 29). How to break through a workout plateau. Sweat. https://www.sweat.com/blogs/fitness/workout-plateau.

Disclaimer: This blog post is not intended to replace the advice of a medical professional. The above information should not be used to diagnose, treat, or prevent any disease or medical condition. Please consult your doctor before making any changes to your diet, sleep methods, daily activity, or fitness routine. iFIT assumes no responsibility for any personal injury or damage sustained by any recommendations, opinions, or advice given in this article. Always follow the safety precautions included in the owner’s manual of your fitness equipment.