The best exercise intensity for fitness gains, according to science

A friend of mine ran for the University of Arkansas during its tenure in the 1990s. Each fall, a new group of wide-eyed recruits will show up for their first workout with NCAA champions and Olympians from around the world. The coach will assign you a session — five times a mile, for example — and send you to the start. Then the nervous rookies will turn to the veterans. “So, how fast are we supposed to cover these miles?” They will ask. “I don’t know,” the veterans will answer deadpan. “How fast He can Do you manage them?

One of the fundamental challenges of training is finding the right intensity. These days, instead of interval training as intense as possible, many runners have adopted what is called “Norwegian method“, using lactate measurements or heart rate monitors to confirm this no Push hard. But there is still a lot of debate about how hard the ideal workout should be. A New study in Medicine and science in sports and exercise She suggests a surprisingly simple answer: It should feel like a 7 on a 0 to 10 effort scale. And even if you think that answer is… also Simple (which you definitely should), the study contains some interesting insights into the physiology and psychology of optimal exercise.

What the new study found

A research team led by Daniel Bock of the University of Zagreb in Croatia recruited 17 runners to do a series of three workouts. Each workout was 3 x 3:00 intervals with 2 minutes of rest. The required intensity was either 6, 7 or 8 Scale from 0 to 10a range that corresponds to somewhere between “difficult” and “very difficult.”

The result that most interested the researchers was: How much time did the runners accumulate with more than 90 percent of VO2 max? VO2 max is a measure of aerobic fitness, and represents the maximum rate at which you can take oxygen into your lungs, absorb it into your bloodstream, pump it to your muscles, and use it to help fuel your muscles. To become fitter, you need to spend as much time as possible in that maximal or near-maximal state so that your body adapts to be able to process more oxygen. If you exercise too easily, you’re not pushing the system to adapt. If you try too hard, you will get tired very quickly. Between these two extremes, there is a sweet spot that increases your time near VO2 max.

Here’s a graph showing the fraction of exercise time spent at more than 90 percent of maximum heart rate (black bars) and more than 90 percent of VO2 max (white bars), for the three different exercises at effort levels 6, 7, and 8:

For both heart rate and VO2, exercising at effort level 6 is less effective for accumulating time above the 90th percentile. The two hardest exercises, at effort levels 7 and 8, are essentially the same, with no significant differences between them. That’s why researchers claim that 7 out of 10 is a good score: you get more training benefit from effort level 6, and there’s no additional training benefit from going up to level 8.

Fast food in the real world

Despite the above finding, the study’s main message isn’t that you should do all of your workouts at an effort level of 7. For one thing, this particular workout involved just nine minutes of hard effort — and you can see in the graph above that time that over 90 percent of your maximum heart rate has already peaked. What if you want to do a longer workout, like 6 x 3:00 or 3 x 6:00? The sweet spot for increasing time above 90 percent is probably a little less effort.

From the researchers’ point of view, the main finding is simply that perceived effort serves as a way to guide exercise. The harder runners are asked to push, the faster they run and the harder they breathe (or more accurately, the more air they inhale and exhale each minute). Given that they were running around a track with no clock and no indication of how fast they were going, this isn’t as trivial as it sounds – but it confirms that we intuitively understand the difference between giving 6, 7 or 8 out of 10 efforts.

There is a more subtle nuance that is also important. Competitors were asked to walk so fast that their efforts matched the target level (e.g. 7) In every moment of the break. So they weren’t guessing what steady pace would correspond to a 7 effort at the end of three minutes — they started fast and then gradually slowed down throughout each interval as they got tired, adjusting the pace so it always felt like a 7 out of 10.

That’s a weird way to run. A decade ago, I tried a trial VO2 max protocol based on the same principle: In each two-minute phase, I was supposed to adjust my pace to maintain a certain perception of effort, which meant starting fast and then slowing down. The final phase was supposed to require maximum effort, which meant starting with an all-out sprint and gradually slowing down the treadmill enough to avoid falling backwards. I was suspended from a safety belt attached to the ceiling of the laboratory, just in case I misjudged. It was brutal, and I threw up shortly after finishing the test.

The result of this fast-start pattern is that people in Bock’s study ended up spending more time at 90 percent of their VO2 max than they would have if they had done each interval at a constant pace. Bock and colleagues suggest this may mean it’s a better way to run intervals that would lead to greater fitness gains. I understand the logic, but I think this is a claim that needs to be verified through a multi-week training study. To be honest, I’m also having a hard time imagining working out this way (probably thanks to the vomit-inducing VO2 max test), and I wonder if you’ll miss out on isometric pace training in races.

For me, the most important finding of the study is simply that harder is not always better. Asking for an effort of 7 to 8 feels worse and may take longer to recover from. But the training signal, as evidenced by factors like lactate levels and time spent above 90 percent of VO2 max, is not stronger. The sweet spot for this 3 x 3:00 workout was an effort of 7 out of 10. We probably can’t take that exact number and automatically translate it to other workouts in other contexts, but we can translate the basic principle: If you want to know how fast you can run your intervals, “as fast as you can” isn’t necessarily the right answer.

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