Strive to perform four to six intervals of HIIT exercises one day per week for 18 to 25 minutes. Justin Check demonstrates some of the most ideal exercises you can do at this level in the video below:
Here is a rundown of what a typical high-intensity interval training routine might look like at the intermediate level.
- Warm up for three minutes.
- Exercise as hard and fast as you can for 30 seconds. Ideally, you should push yourself to "failure" — this is the part of the exercise where you can no longer maintain good form, but still be able to perform another repetition.
When you reach failure, it would be very difficult, if not impossible, for you to continue the exercise for another 10 seconds, as you just don't have that much oxygen left to contract your muscles.
You should be gasping for breath and feel like you couldn't possibly go on another few seconds. It is better to use lower resistance and higher repetitions to increase your heart rate.
- Recover for 90 seconds, still moving, but at a slower pace and decreased resistance.
- Repeat the high-intensity exercise and recovery up to seven more times. However, at this level, you will likely only be doing four to six. As you get fitter, just keep adding repetitions gradually until you're doing eight during your 20-minute session. Remember never to do these exercises more than three times a week or you will compromise your recovery.
HIIT vs. Circuit Training: What's the Difference?
HIIT and circuit training are both fast-paced, intense workout routines that are often confused with each other, but there are key differences between them. HIIT is primarily focused on performing a particular workout in varying intensities and circuit training is all about cycling through different exercises.
HIIT is generally used for cardio workouts, although you can add weights to increase the intensity. Meanwhile, circuit training consists of six to 12 "stations," where you'll perform a combination of cardio and strength exercises to target different muscle groups. Each station ideally takes 30 seconds to three minutes to finish.
Unlike HIIT, which has a predetermined recovery period between intervals, circuit training requires minimal rest between stations to keep the heart rate up. You may be able to complete an entire circuit within 30 minutes to an hour, depending on your goals and fitness level. A HIIT session, on the other hand, can be completed within 20 minutes.
One of the most important distinctions between the two routines is that in circuit training, you can control the intensity of your workout — you can start at low intensity and eventually ramp it up as you cycle through your routine. In HIIT, your goal is to perform the exercise at maximum effort from the get-go.1,2
Adding HIIT Can Shorten Workout Time
Adding HIIT into your workout routine is a great way to reduce the time you spent exercising while increasing the benefits that you reap from your workout. In a 2016 study published in PLOS ONE, three groups of sedentary men doing different exercises were evaluated for 12 weeks.3
One group was a control group, another did sprint interval training (SIT) for three weekly sessions, while the other group performed moderate-intensity continuous training (MICT). The results show that doing brief strenuous exercises is just as effective in improving cardiometabolic health as a moderate-paced workout done for a longer period of time.4
HIIT also triggers mitochondrial biogenesis, which may help slow down aging by reversing age-related declines in mitochondrial mass.5 As I've previously explained in my book, "Fat for Fuel," mitochondrial dysfunction is at the heart of many chronic diseases. Hence, doing a workout that supports mitochondrial biogenesis may help bolster your defenses against mitochondrial dysfunction and increase your longevity.
Know Your Target Heart Rate Zone to Maximize Your Workout
It's vital for you to determine your heart rate and work out until you reach your optimal heart rate zone, or the state wherein your body can perform better and retain that same energy for a period of time. The heart rate zone can be classified into three levels:
- Aerobic/low-intensity — 50% to 75% of maximum heart rate (MHR) or HRR
- Anaerobic/moderate-intensity — 75% to 85% of MHR or HRR
- Anaerobic/high-intensity — 85+% of MHR or HRR
If you're unsure about your MHR or HHR values, you can compute them through these ways:
- MHR — Declan Connolly, Ph.D., recommends getting your heart rate up as high as you can through this method:4
"A simple test I have proposed over the years is going out onto an outdoor track, jogging 400 meters (1/4 mile) as a light warm-up, then running [the same distance] as fast as you can. Repeat that entire sequence two more times, for a total of six laps — three jogging and three fast [running]. Check your heart rate right after the third set. Whatever that number is after the last lap is a good indication of your MHR."
If you're unable to run for whatever reason, or if you're prone to injury from running, you can do this exercise on a stationary bike or other machine. Make sure to use the same set structure and time sequence. Consult a personal trainer if you need assistance.
- Heart rate reserve (HRR) — Dr. Bryant Walrod, team physician at The Ohio State University, suggests a different technique that involves first calculating your MHR using this formula: 208 minus (0.7 x your age).
If you are 25 years old, your target maximum is 190.5 beats per minute. Walrod claims this formula becomes more accurate as you get older. Afterward, find your RHR by either using a heart rate monitor or counting your heartbeats for 60 seconds when you are sitting down in a relaxed state.
Finally, use those two numbers to calculate your HRR as follows: MHR minus RHR equals HRR. Waldrod notes that your RHR will drop as you get fitter. Your RHR will change if you're consistent, so make sure to check the number at least annually. Some say that HRR provides a better target heart rate to achieve optimum levels of exertion based on both your maximum and RHR.