No, killing yourself at high intensity won’t get you to your goal faster—but slowing down, even more than your “recovery” pace, just might.
Nowadays, getting in a good workout seems to be synonymous with being reduced to a shaking—potentially vomiting—pile of sweat. Easy runs? They are just too, well, easy.
After all, in the past decade, research has consistently shown that minute-per-minute, going hard results in bigger calorie burns and greater effects on metabolic health, including insulin sensitivity, or how effectively your body uses and absorbs blood sugar, and VO2 max, or how efficiently your body uses oxygen.
“Plus, people find repeats and intervals inherently more interesting than going out and jogging at a super slow speed for 45 minutes,” explains running coach Matt Fitzgerald.
But—at least in the endurance realm—a focus on high-intensity exercise may very well be running its course, with physiologists and run coaches campaigning hard for a reduction in exercise intensity.
For instance, Janet Hamilton, C.S.C.S., owner of Atlanta-based company Running Strong, explains that every intensity—not just high—has benefits, and where you spend the majority of your training time should depend first and foremost on your goal.
If your goal is improving your performance at any race that takes more than one minute to complete (think: anything longer than a 400-meter dash), that intensity is likely going to be lower than even your current so-called “recovery” days.
“There’s a common misunderstanding that low-intensity and high-intensity exercise do the same thing, but high-intensity does it better,” Fitzgerald says. “There is overlap, but they also do unique things. Low-intensity exercise has some benefits that high intensity does not—and vice versa.”
What Is Intensity Anyway?
The gold standard for determining how hard you’re working during any given workout revolves around the two ventilatory thresholds. The first ventilatory threshold (VT1) is the intensity at which lactate rises above resting levels, and typically occurs around 78 percent of your max heart rate, according to Fitzgerald. However, in people who are newer to endurance exercise, it can be at a much lower heart rate.
Once you hit VT1, you’re no longer able to chat comfortably, but can still string together a few words and short sentences, explains Carl Foster, Ph.D., director of the Human Performance Laboratory at the University of Wisconsin–La Crosse.
At the second ventilatory threshold (VT2)—a.k.a. anaerobic threshold or lactate threshold—lactate begins to accumulate in the blood much more quickly, and your breathing becomes rapid. This typically occurs around 85 to 95 percent of max heart rate. But again, the more aerobically trained you are, the higher than heart rate will be when you do cross VT2. Once you do, talking is close to impossible and exercise duration will decrease—your body just can’t sustain it very long, Foster says.
Benefits of Low-Intensity, Steady-State Cardio (LISS Cardio)
By definition, if you’re in it to win it (or set a PR), your race pace is going to be high-intensity. A shorter race like a 5K might have you at around 95 percent of your max heart rate, Hamilton says, while a 10K might have you at about 90 percent and a marathon would be roughly 85 percent.
That raises the question: Why train at a lower intensity?
By doing so, you’ll actually build up your aerobic capacity, which allows your body to break down carbs and fat into energy, strengthen your slow-twitch muscles (which fire during sustained efforts), and transport oxygen more effectively.
What’s more, Foster explains, your ability to store glycogen (carbs in the liver and muscles) increases.
“If you are doing a long run every two to three days [as opposed to something more intense], your fuel tank gets bigger,” Foster says. And then, once your body does run out of glycogen, it more efficiently turns to fat for fuel to keep you from hitting the wall.
Not to be overlooked, however, are the mental benefits of low-intensity, long-duration exercise. “The brain adapts to exercise more than any other organ in the body does,” Fitzgerald says. After all, at a certain point, endurance is as much—if not more—mental than it is physical.
How to Up Your Low-Intensity Work
Most coaches recommend that endurance athletes, no matter their level of competition, should perform 70 to 80 percent of their training below their VT1, 5 to 10 percent between VT1 and VT2, and a max of 20 percent of above VT2, says Foster.
Previous research supports doing the bulk of your training at a long duration and low intensity, with just a few high-intensity workouts thrown in—this will optimise your endurance performance in the long run. In fact, even the world’s top-performing athletes use this method.
Most runners are training way too hard. According to Fitzgerald, the average runner spends about half of their weekly training time at a moderate intensity. They naturally gravitate to a pace that they find seriously challenging—but not too uncomfortable. The result? A lot of miles ran end up being “junk miles” and don’t allow runners to properly recover from their workouts or build their aerobic capacity up.
The first step in finding a better balance is to determine what high-, moderate-, and low-intensity exercise looks like for you. To calculate your max heart rate—and your target heart rate zones—the ‘ol “220 minus your age” equation will give you a rough idea.
But for a more precise measure, perform some field testing. Fitzgerald recommends warming up and then running a 30-minute race on a flat, smooth course. Your average heart rate for the final 20 minutes of those 30 represents your max.
Pretty similarly, Hamilton says that you can take the greatest sustained heart rate in a 5K as a pretty accurate guide of max heart rate. “For example, in a 5K, if the athlete saw a peak heart rate of 198 but a sustained high heart rate of 188 for the last 5 minutes of the race, I’ll use the 188 rather than the 198,” she says.
A less complicated measure is to simply gauge your ability to talk during a run. When talking during exercise is “unequivocally comfortable” during a run, that means you’re operating below VT1 at a low intensity, says Foster. Between VT1 and VT2, you should be able to speak in short sentences, and you won’t really want to engage in deep conversation with your running buddies. “After VT2, you can only say two to three words at a time, and they are going to be things that your mama wouldn’t want you saying,” he says.
Then, devote roughly 80 percent of your overall total running mileage or time to that comfy exercise, Foster says. The rest should be broken up between moderate and high intensity, with the majority skewing to that puddle-inducing level of exertion you already know and love.
