Gauging Workout Intensity: How Hard Should You Go?

By Shelby Stoner, PHASE IV Exercise Physiologist

How many times have you hit the track, gone to spin class, or hopped on a treadmill to do your routine workout, and by the 5th minute your heart is beating out of your chest, you’re hyperventilating, or dripping in sweat? Too often we go out too eager, too hard, or too fast and burnout too soon. And the problem isn’t just the pace, your legs or your lungs- it’s your heart rate. What many people don’t realize is that your heart rate is actually a measure of your exercise intensity, i.e. the harder the workout is, the higher your heart rate will go. And as most of us know, what goes up must come down. The key to understanding your exercise heart rate / heart rate zones is to understand what system you’re working- the aerobic system, anaerobic system, or your lactate threshold.

This is why we implement VO2 testing at Phase IV, in order to determine the fat-burning zones and heart rates where your body is efficient in using fat for fuel as compared to carbohydrates. If you’re working with a heart rate monitor, it’s easy to see exactly what zone you’re working in throughout the workout. However, if you don’t have a heart rate monitor or assigned zones (yet!), there are other physical markers to assess exercise intensity such as the “talk test.”

For example, if you are able to speak in full sentences while exercising, you are most likely performing aerobic (with oxygen) work, and can also be considered as fat burning exercise. The purpose of working in the aerobic zone is to accustom your body to favor burning fats over carbohydrates and spare muscle glycogen. In addition, the benefits of burning fat include that it is a much more efficient fuel providing more energy than carbohydrates per gram, it is abundantly available, and it does not produce lactic acid. Most of your training should be in this aerobic zone.

If you can only get out a few words at a time, you’re most likely at your lactate threshold. The purpose of training at your threshold is to train your body to metabolize lactate, and allow you to work harder yet maintain lower lactic acid levels. Training within this zone will elevate your lactate levels slightly, and helps improve your lactate tolerance. As your body adapts you will start to produce less lactate because it will be using more fats than before, and your body will be more efficient at removing accumulated lactic acid. The benefit of this zone is that you will be able to work for longer periods. Over time, you will be training your body to move faster without a large buildup of lactic acid.

Finally, if you can barely get out one or two words, you’ve probably found yourself in the anaerobic or submaximal zone. Training at submaximal levels can be used as part of interval training, which focuses on improving power output and anaerobic endurance when a lot of energy is needed quickly, but will not last long.

The benefit from using tools such as heart rate training or utilizing the “talk test” during exercise is to measure exactly which of these zones you are working in. Your body can become very efficient at burning fat for energy so it can last a long time. Over time, and with the right type of training, the pace at which you can do this will improve, i.e. running faster at the same heart rate. However, if you consistently push yourself into zones like the lactate threshold and anaerobic zones, you won’t train the fat burning system of your body. By consistently training at high heart rates, your body will become tired and fatigued, which will actually cause your heart rate to be higher while at slower paces. Eventually, exercising at a heart rate that’s too high for the purpose of your training will lead to a plateau, burnout, or injury.

So you’re out for a long run or cycle, and you notice your heart rate rising (without coming back down), your breathing becomes heavier, and possibly feel dizzy, what do you do now? It’s imperative in situations like these that you not only listen to your heart rate, but other physical markers such as your breathing or focus. Although you may want to be competitive while training with friends or beating someone’s time on Strava, it’s important to remember that workouts are not meant to be won or lost. So if you find yourself in a situation where you feel yourself pushing too hard, take a moment to slow down for a minute or two, walk for a bit, or stop altogether and take a few moments to gather your composure and breath. While it may seem counterintuitive, working harder isn’t always better.

While using the “talk test” is a great tool to see if you’re training in the appropriate zones, the numbers used from VO2 testing don’t lie. Scientific VO2 testing allows us to get an inside look at your exercise metabolism, i.e. how well your body uses fat for fuel while measuring your current fitness level and aerobic capacity. From the results of the testing, we line out specific heart rate training zones that are tailored to you and your own physiology, making each workout more effective and efficient.

Looking for personalized exercise and training guidance?

At PHASE IV we create customized daily training plans that are designed to boost performance and optimize your metabolism. Call us to schedule a complimentary 30-minute consultation at our facility in Santa Monica. 310-582-8212

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