Is high-intensity interval training (HIIT) really the answer to weight loss and improved cardiorespiratory health? In the last few years, HIIT workouts have become the “go-to” cardio. Word on the street is that if you’re not doing interval training, you’re training inefficiently.
HIIT typically means circuit training, metabolic resistance training, or simply work/recovery intervals on a cardio machine. It’s currently the “hot” method of losing weight and increasing V02 max.
I am not against HIIT at all, but I do think it’s important to look critically at the costs/benefits more closely. As Lyle McDonald states, HIIT has been touted as always better than conventional steady-state cardio, and this is simply not true .
A recent article by the National Academy of Sports Medicine (NASM) analyzed HIIT workouts critically, and I summarize for you here:
- Calories burned during exercise. Studies show that doing HIIT workouts for 45 minutes (60 seconds work to 120-second recovery intervals) at an intensity greater than 85 percent maximal performance burns 454 calories, with 91 calories derived from fat. By contrast, a 45-minute running workout at an intensity of 65 percent results in 490 calories burned, with 221 fat calories derived from fat. So in order to burn the around same number of calories with HIIT, you’d have to work MUCH harder for the same amount of time.
- Calories burned after exercise. This leads us to the “afterburn” effect, or excess post-exercise oxygen consumption (EPOC). Research shows that the higher the intensity of exercise, the more calories are burned post-exercise (potentially up to 14+ hours). However, it is impossible to measure exactly how many extra calories are burned and estimates might be overestimated. As the NASM article points out, calories burned as a result of EPOC most likely need to be measured over a long period of time in order to assess the pounds lost.
- Metabolic health. In simple terms, the higher your mitochondrial density, the better your body can metabolize fat. Exercise increases your mitochondria, and according to Dr. Iñigo San Millán, endurance cardio does this best. Of course, any exercise will help your metabolism flexibility. As Dr. San Millán emphasizes, exercise is medicine. He also maintains that we’ve wrongly abandoned endurance cardio in favor of HIIT.
- Overall health. HIIT has been shown to improve V02 max and insulin sensitivity. Since endurance cardio has these same benefits, the advantage of HIIT workouts are that they take less time.
Takeaways on HIIT Workouts
Here’s what you need to consider when using HIIT in your training program:
Can the average deconditioned person realistically perform long bouts of HIIT?
From my experience as a personal trainer and from a biological perspective, the answer is no. A deconditioned individual doesn’t have the capacity to do 15 work intervals at 85 percent intensity. If they manage to complete the session, they most certainly would take awhile to recover and probably will quit in discouragement.
The fact is, if you are deconditioned and want to lose weight or improve your health, you need to start slow. This should happen in stages: After you’re able to train at a low intensity for at least 30 minutes three times a week, you can progress to short work-to-rest ratios (1:3). Once your fitness improves you can move to longer work-to-rest periods (1:2 and eventually 1:1).
You’ll notice that the work-to-rest ratio decreases while the duration of HIIT stays the same. As your conditioning increases you can also increase the duration, but as you can see, this is a process that takes time.
Even though EPOC benefits are arguably small, individuals might be mislead into thinking they MUST do HIIT workouts to optimize calorie burn. But there are a lot of benefits to endurance cardio, including improvements in fat oxidation and insulin sensitivity .
Is it necessary or healthy to train at a high intensity year round?
It’s common knowledge that periodization is the most effective, safe way to train. Personal trainers (including myself) who are skilled at program design use periodization to ensure steady progress and avoid injury.
Periodization for endurance athletes means training at a low intensity most of the year and ramping up to high intensity closer to competitive events.
For those who use resistance training to increase muscle and strength , periodization means rotating high- and low-intensity phases every few weeks (linear periodization) or alternating high- and low-intensity sessions during a single week (undulating periodization).
Whichever method you use and whatever types of exercise you do, you need periods of rest and recovery. Doing HIIT multiple times per week for long periods of time can lead to overtraining and injury, just as always lifting heavy without a break can lead to injury. When the body doesn’t have time to restore itself, it simply breaks down.
HIIT does a good job of oxidizing fat and improving insulin sensitivity, but so does traditional steady-state cardo. The main benefit of HIIT is that you can exercise for less time for similar benefits; however, if you are deconditioned this will be challenging. And everyone should cycle in HIIT or use it moderately to avoid plateaus and injury. When integrating HIIT, start slowly and consider your goals.
Leave your comments below – would love to hear your takeaway.