What Is Zone 2 Fitness Training?

As an avid cyclist, runner, and overall endurance athlete, I’ve followed with interest the concept of polarized training, which sees most workouts happen at a comparatively easy pace, the better to set up for occasional high-intensity workouts.

The approach is said to boost aerobic fitness and promote longevity. One of the world’s experts in the topic is the Texan kinesiologist, Dr. Stephen Seiler, who moved to Norway early in his career, was an executive board member of the European College of Sports Science and has worked as a scientific advisor for everyone from elite cross-country skiers to cyclists and distance runners. (Today, he’s a professor of sport science at Norway’s University of Agder.) I recently spoke with Prof. Seiler to hear his thoughts on polarized training, how he’s used it to improve the fitness of Olympic athletes and how the approach could benefit even armchair athletes. Here’s what I learned.

What does Zone 2 fitness training mean?

Zone 2 fitness training is a form of polarized fitness training that sees athletes limit the intensity of most workouts to a “green zone”—an intensity where the perception of exertion is relatively comfortable. The approach also is referred to as polarized training, 80/20 training, or green zone training.

Generally, athletes spend three or four out of every five sessions working at a “low” intensity. Then, the last of the five-session cycle is about as hard as possible, seeing the athlete training well beyond their lactate threshold.

“There are only 24 hours in a day,” Dr. Seiler told me. “You can only handle so much training, so much stress—so you’ve got to optimize it.”

What are the different zones of cardio?

Across sports and around the world, many different groups use various labels for the zones of aerobic intensity. Some simply say low, moderate and high intensity. Dr. Seiler prefers to divide the aerobic zones into green, yellow and red. Others categorize the intensities into five different zones. Regardless of what you call them, it helps to identify your thresholds as you advance into the next zone.

• Zones 1 & 2 / Green: Below the first blood lactate threshold, blood lactate under 2.0 mmol, low-intensity, aerobic talking pace
• Zone 3 / Yellow: Blood lactate increases but can stabilize, higher perceived exertion, heavier breathing, talking is possible but difficult
• Zones 4 & 5 / Red: Very tough, hard breathing, pace achievable for at most a few minutes, conversation impossible

The key is to use your personal thresholds (where you cross over into the next zone) as markers for your training sessions. Once you know your zones, you can confidently spend longer durations in the green zone and make specific decisions over how much time you spend in yellow and red.

Why should I stay in Zone 2 when that doesn’t push me very hard?

Dr. Seiler shared his experience with athletes who continually pushed themselves to stay in the yellow and red zones during a workout. “What was supposed to be a nice, aerobic, green zone, talking-pace group ride,” explains Dr. Seiler, “begins accelerating its way up into a threshold ride. Then the athlete is more tired than he or she should have been. The next day, they were supposed to do a interval session, but they’re tired.” Consequently, Dr. Seiler explains, the athletes fail to achieve the zone four or five intensity that really would have benefited their training. Instead, the quality of that next-day session goes toward zone 3—which isn’t optimal for aerobic conditioning.

“Let easy be easy,” Dr. Seiler reminds us. It can be difficult to maintain that moderate-intensity, green-zone ride, and resist the urge to kick it up a notch, but Dr. Seiler points out that keeping things light will set you up to have the energy for the high-intensity workout the following day.

How much time should I spend in each zone?

There is no single right ratio for everyone, Dr. Seiler says. But in general, he says, and depending on age, season, distance, and the intended purpose of your training—the optimal ratio is somewhere between 70 easy/30 hard, and 90 easy and 10 hard. This means that an athlete, whether amateur or best-in-class, should be spending 70-90% of their workouts in that comparatively easy, talking pace, green Zone 2.

Are you interested in a fitness training program that incorporates the Zone 2 model? At Medcan, we’re passionate about helping you live well, for life. Book a consultation or personal training session by emailing fitness@medcan.com.