Why Your Hardest Workouts May Be Too Much

A friend of mine went to the University of Arkansas in his reigning years in the 1990s. Each fall, a new batch of wide-eyed recruits will show up for their first workout alongside returning NCAA champions and Olympians from around the world. The coaches will set a session — five times a mile, say — and send them to the start. Nervous competitors would then turn to veterans. “So, um, how fast should we run these miles?” They will ask. “I don’t know,” the veterans would reply in surprise. “How fast can Do you run it?”

Finding the right intensity is one of the fundamental challenges of training. These days, instead of trying to figure out how hard it is over time, many runners opt for the so-called “Norwegian method,” measuring lactate or using heart rate monitors to make sure. don’t Push harder but there is still a lot of debate about how difficult the ideal workout should be. In a new study Medicine and Science in Sports and Exercise A surprisingly simple answer suggests: It should feel like a 7 on an effort scale of 0 to 10. And even if you think that is the answer too Simply put (which you definitely should), the study has 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 perform a series of three workouts. Each workout was 3 x 3:00 intervals with two minutes of rest. The intended severity was either 6, 7, or 8 on a scale of 0 to 10, a range that corresponds to somewhere between “severe” and “very severe.”

The results the researchers were most interested in were: How long did the runners accumulate more than 90 percent of their VO2 max? VO2 max is a measure of aerobic fitness, representing 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 fuel your muscles. To get fitter, you want to spend as much time as possible in this maximal or near-maximal state so that your body is able to process more oxygen. If you’re going too easy on the workout, you’re not pushing the system to adapt. If you go too hard, you will tire quickly. Between these two extremes, there is a sweet spot that gets your time closer to VO2 max.

Here’s a graph showing a portion of exercise time spent above 90 percent of heart rate (black bars) and above 90 percent of VO2 max (white bar), for three different workouts with effort levels 6, 7, and 8:

For both heart rate and VO2, exercise at effort level 6 is less effective for accumulating time above 90 percent. The two hard workouts, effort levels 7 and 8, are essentially the same, with no statistically significant differences between them. That’s why researchers claim that 7 out of 10 is the sweet spot: you get more training benefits from 6 levels of effort, and no more training benefits beyond 8 levels.

Real world views

Despite the results above, the primary message of the study is not that you should do all of your workouts at 7 attempts. For one thing, this particular workout only involved nine minutes of hard effort—and you can see in the graph above that the heart rate was raised above 90 percent. If you want to do a longer workout, like 6 x 3:00, or 3 x 6:00? The sweet spot that maximizes time above 90 percent is probably a little lower effort.

From the point of view of the researchers, the main way is simply that the attentional effort acts as a guide to the instructions. The harder the runners were instructed to push, the faster they ran and the harder they breathed (or more precisely, the volume of air they inhaled and exhaled per minute). Given that they’re running for around an hour and have no clue how fast they’re going, it’s not as trivial as it seems—but it does confirm that we intuitively know the difference between a 6, 7, or 8 out of 10 efforts.

There is a very subtle nuance here that is also important. Runners were told to pace themselves so that their effort corresponded to a target level (eg 7). Every minute of the interval. So they didn’t anticipate a steady pace that would correspond to 7 attempts at the end of three minutes—they started fast and gradually slowed down during each interval as they tired, adjusting the pace to always feel like 7 out of 10.

This is a strange way to run. A decade ago, I tried a VO2 Max protocol based on the same principle: for each two-minute step, I had to adjust my pace to maintain a certain level of effort, which meant starting fast and slowing down. The final phase was supposed to be maximal effort, which meant starting a total sprint and gradually lowering the treadmill just enough to avoid falling off the back. I was suspended on a safety flag attached to the ceiling of the lab, just in case I thought wrong. It was brutal, and I threw up shortly after the exam was over.

The result of this fast start pattern is that the subjects in Bok’s study spent more time at 90 percent of their VO2 max than if they had run each interval at a constant pace. Bock and his colleagues suggest that this may mean that it is the best way to do interval running that produces the biggest fitness gains. I understand the logic, but I think this is a claim that needs to be confirmed with a few weeks of training studies. To be honest, I also have trouble imagining running workouts this way (probably thanks to that vomit-inducing VO2 max test), and wonder if you’re even missing out on running workouts for races.

For me, the most important concept of the study is simply that harder is not always better. Dialing 7 to 8 attempts feels awful and may take longer to recover from. But the training signal, as indicated by parameters such as lactate levels and time spent above 90 percent of VO2 max, is no longer strong. The sweet spot for this particular 3 x 3:00 workout was 7 out of 10 attempts. Maybe we 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 to run your intervals, “as fast as possible” isn’t necessarily the right answer.

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