What Will Adding High Intensity Workouts to My Training Do for Me?

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Question:

“I just did my first intensity workout. Ever. Not too bad. What’s it going to do for me?”

Author and Coach Matt Fitzgerald Answers:

First of all, congratulations! High-intensity exercise is something many people avoid for their entire lives, which is too bad, because it does a variety of good things for the body (and mind). These benefits fall under two basic categories: health benefits and fitness benefits. If you’re a nonathlete, you’re probably most interested in the former, whereas if you’re a runner or another type of athlete, you may care more about the latter, although there is a lot of overlap between the two categories. Weight loss, to name just one, is a proven outcome of high-intensity exercise that enhances health and running performance alike.

Let’s take a closer look at both the health and the fitness benefits of high intensity exercise.

Health Benefits

High-intensity workouts almost always take the form of intervals, or short bursts at high speed separated by slower, active-recovery periods. For example, you might warm up with 5 to 10 minutes of easy jogging and then complete six or eight 30-second sprints, each followed by 90 seconds of slow running, before cooling down with another 5 to 10 minutes of easy jogging. High-intensity interval training, or HIIT, as it’s known, has been intensively studied, and its health benefits are well established.

A 2019 study by Spanish researchers investigated the effects of HIIT on adult men and women with metabolic syndrome (a combination of excess body fat, high blood pressure, abnormal cholesterol and triglyceride levels, and high blood sugar). For a period of 16 weeks, 56 men and 63 women with metabolic syndrome completed three HIIT sessions per week. The researchers used a statistical tool known as the MetS Z-score, which incorporates measurements of all five components of metabolic syndrome, to assess the results—which were impressive. Among the female subjects, HIIT reduced the MetS Z-score by half, and the male subjects fared even better.

Other proven health benefits of HIIT include stress reduction and improved memory. While low-intensity exercise offers many of the same benefits, HIIT does so in a far more time-efficient manner. A 2013 study published in the Journal of Physiology reported that subjects who did three HIIT sessions per weeks, each last just 12 minutes, saw health benefits equaling those achieved by other subjects who completed five, 40-60-minute low-intensity workouts per week.

Fitness Benefits

If you’re a runner or other athlete chasing performance goals, you have just as much reason to include high-intensity workouts in your routine. HIIT is proven to increase important fitness measures such as aerobic capacity (or VO₂max), anaerobic capacity, and lactate threshold beyond the levels that can be achieved through low-intensity exercise alone.

Collectively, these benefits translate to faster race times. This was shown in a 2017 study by a team of Brazilian and Australian researchers. Eight recreational runners were asked to substitute a portion of their normal training with twice-weekly HIIT workouts for a period of four weeks, while eight others continued to train as normal. On average, those in the HIIT group lowered their 5K times by 28 seconds, whereas members of the second group saw no improvement.

High-intensity workouts aren’t easy, but that’s actually part of the reason they’re so effective. Another 2017 study, this one by British scientists, found that six weeks of HIIT elevated performance in a time-to-exhaustion test partly by increasing pain tolerance.

It would be a mistake to conclude from such findings that HIIT is simply “better” than low-intensity exercise, however. Other research has demonstrated that endurance athletes, including runners, tend to improve most when they limit high-intensity work to 20 percent of their total weekly training time.

The reason appears to be that, because HIIT is quite stressful to the body, a little goes a long way, and more than a little is counterproductive. Low-intensity exercise, meanwhile, being much gentler, can be tolerated in larger amounts and indeed must be done in larger amounts to yield maximum benefits.

So, while I’m glad that you’ve discovered the joys of high intensity, don’t leave low intensity behind!

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Matt Fitzgerald’s most recent book is: Life Is a Marathon: A Memoir of Love and Endurance.