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Cardio Zone Training: Part 2 of 3—Threshold

By L.K. Regan

This article is part two of's three-part series on cardio zone training from Devin Wicks (ACSM-HFI, USAW Club Coach), a fitness operations director at the University of California, Berkeley, and specialty strength coach for some of the University's premier sports teams. Zone training, in which you target and then sustain particular ranges of an elevated heart rate, is the key to gaining the full range of benefits—muscular, cardiovascular, and metabolic—from cardiovascular exercise. You can use cardio zone training to become more fit and faster, and to develop more stamina.

If you haven't yet done so, please see Cardio Zone Training: Part 1 of 3—Endurance to get a background on the program, learn how to use your rate of perceived exertion to calculate your heart rate, and get your endurance-training program. After completing this week's program, you can move on to Cardio Zone Training: Part 3 of 3—Speed to complete the program.

Threshold Zone Training
Now that you’ve pedaled your way to greater endurance, you're ready to work at a higher heart rate, closer to your maximum. This is the phase called threshold training, in which you will try to move the point of exertion at which your body begins to use anaerobic respiration. “Major indicators of fitness are your resting heart rate and your threshold rate," says Wicks. "The fitter you are, the lower your resting heart rate and the higher your threshold.” Increasing the distance between these two measures is a major goal of athletes, as a higher threshold means an increased capacity for work.

Your anaerobic threshold is the point at which your cardiovascular exercise causes your muscles to produce more lactic acid than your body can absorb. Ordinarily this occurs at around 85 percent of your maximum heart rate. At this point of exertion, your muscles will start burning glycogen in addition to fat to acquire energy. This sounds good, and it is from the point of view of burning many, many calories—but unfortunately, the lactic acid is so fatiguing to your muscles that you can’t sustain this level of exertion for very long.

But if you could raise the point at which lactic acid began to make you fatigue, while continuing to push your heart rate higher, you would both burn a maximum of calories and develop your overall fitness, allowing you to out-run, out-cycle, and plain old out-do people of the same talent and skill level who did not train in this zone. Threshold training, therefore, teaches you to work at that anaerobic tipping point, and, over time, to shift your threshold itself to take place at a higher heart rate. Moving that point even a small amount will require time and determination—but small movements in your threshold will make a huge difference in your fitness level. “All other things being equal," says Wicks, "if your threshold is higher, you can go for longer at a higher intensity. And that is a definition of being more fit.”

Notes on the Threshold Training Program
For the threshold portion of this program, Wicks has chosen the treadmill. The program is intended to be done at least three times per week during your threshold weeks, and no more than five times per week.

You want to run for an extended period while incorporating short, managed bursts that go to 85 to 90 percent of your maximum heart rate. “This will be as close to sprinting as you can get without actually sprinting,” says Wicks. In other words, go hard, but not all the way to your limit. How will you know when you’re going hard enough? As with your endurance training, Wicks has used an RPE (Rate of Perceived Exertion) scale to judge your percentage. To learn how to use this scale, see Cardio Zone Training: Part 1 of 3—Endurance, the first article in this series.

The treadmill has two variables for you to work with, speed and incline. You can easily fall into the trap of only using speed as a means of increasing intensity, but in fact you want to balance both variables; try to add a bit of both speed and incline when it’s time to take it up a notch. This will help to keep you at a speed that you can control, and reduce the risk of injury.

Phase Exercise Time RPE Description
Warm-up Treadmill 5 mins 3 - 4 With the incline set to zero, jog on the treadmill to warm up your body. Try to set a steady, easy pace, getting your breathing going.
Threshold Training Phase Treadmill 4 sets of 5 mins each (20 mins total) Varies Repeat the following five-minute set four times, without stopping or slowing down between sets:

Minute 1: Run on the treadmill at an RPE of 5 for one full minute (at about 60-65% of your maximum heart rate). This should get you breathing hard and working, but not overly labored.
Minutes 2 and 3: Increase both your speed and your incline by a moderate amount to push your RPE to a 7 for 2 minutes. You’re aiming to be around 70-75% of your maximum heart rate. You should be able to talk, but not eager to do so.
Minute 4: Again increase the speed and incline of the treadmill to bring yourself to an RPE of 8. You should now be at 80% of your maximum heart rate, and you’re breathing should be hard. If you don’t have to open your mouth to breathe, you’re not working hard enough.
Minute 5: Dig deep and take your RPE beyond an 8; you’ll need to really push to achieve 85% of your maximum heart rate. Work hard but don't overdo it: Your pace should be sustainable for a minute, not a near-death experience. At the end of minute 5, immediately begin your next set at minute 1. This will make minute 1, for every repetition after the first set, into a working recovery, and will allow your heart rate to come down even as you continue to work.
Cool-down Treadmill 5 mins 4 or below As soon as you finish the last set of the threshold training, immediately reduce the intensity and return to an RPE of 4 to begin your 5-minute cool down. You can decrease the speed and incline over the course of the cool-down to bring your RPE down to a 3, or even a 2, but it’s important after the last set of threshold training not to crash to a halt. Think of the cool down as a working recovery, and adjust as you go.