How long and hard should my cardio workout feel?
One of the easiest mistakes new exercisers can make is to be overzealous—to jack the treadmill up to maximum velocity until they get spat out the back, and repeat that every day until they’re too discouraged and exhausted (and possibly injured) to continue.
Of course, it’s just as possible to be underzealous, flipping through a magazine while absent-mindedly turning the pedals of the exercise bike at a glacial pace. Ideally, you want to be somewhere between these extremes—but where, exactly?
For aerobic exercise, you can divide efforts into three basic zones on the basis of how your body reacts. The easiest is the aerobic zone, where your heart and lungs are able to deliver enough oxygen to your muscles to keep them functioning. In contrast, the hardest, or anaerobic, zone is where your muscles can’t get enough oxygen.
In between is the threshold zone, which is marked by a rapid accumulation of lactate in your blood as your muscles begin to cope with insufficient oxygen. (The terminology, and indeed the science underlying these descriptions, is still a topic of active research and debate. But all sides agree about the practical training advice, so we’ll stick with “aerobic,” “threshold,” and “anaerobic” for now.)
How much time you spend in each of these zones depends on your goals and preferences, but a good general guideline for how to allocate your workout time over a typical week is to aim for 70 percent aerobic, 20 percent threshold, and 10 percent anaerobic.
These ratios are based on studies of elite endurance athletes, who attempt to balance the hard training that brings the largest and swiftest gains in fitness with easier efforts that allow them to recover while continuing to improve. For many novices, the high proportion of “easy” efforts is a surprise—but it’s simply not possible to hammer all the time.
There are many sophisticated ways of figuring out what zone you’re in. Exercise labs, for instance, measure the lactate in your blood at different intensities to precisely determine the speed or heart rate at which your threshold occurs. Heart rate monitors can also be used to monitor training intensity, though it’s important to understand their limitations. Surprisingly, going by feel can be just as accurate as the high-tech approaches, and it has the added benefit of forcing you to pay attention to your body’s signals so that you’ll know when something is amiss.
A 1987 study at the University of Liverpool found that instructing cyclists to pedal with vague descriptions like “somewhat hard” or “hard” was just as good as heart rate at producing a repeatable effort. Since then, numerous studies have confirmed that “perceived exertion” is a reliable way of gauging intensity.
For example, on a scale of 1 to 10, the aerobic zone corresponds to about 3 (moderate); threshold is 5 to 6 (hard); and anaerobic is 7 to 9 (very hard). Only about 10 percent of people struggle with perceived effort, according to University of Wisconsin-La Crosse researcher Carl Foster—mostly control-oriented people (often lawyers or surgeons) who don’t like to admit anything is difficult.
“They’re on a treadmill saying, ‘This is easy, this is pretty easy, this is sort of moderate’—and then they’re going backward off the treadmill,” he says.
An even simpler approach is called the Talk Test. If you’re able to speak in full sentences—out loud, not under your breath—you’re in the aerobic zone. Once you hit the threshold, you’ll start to breathe much harder and only be able to speak in short phrases.
And when you can only gasp out a word or two at a time, you’re in the anaerobic zone. What Foster has found over the years is that, left to their own devices, athletes tend to go too hard on their easy days. (The reverse can also be a problem—note that the aerobic zone should feel “moderate,” not “easy.”) By paying close attention to your effort—and by talking out loud, even if you’re alone—you’ll be able to avoid those pitfalls.
|Heart rate||Below 80% of max||80-90% of max||Above 90% of max|
|A few words at a time||Single words|
|Workouts||20-60 minutes steady||Surges of 3-10 minutes||Short bursts of 0.5-3 minutes|