Training in the “Zone”: Is Your Intensity Level Accurate? Probably Not. Even at Orange Theory Fitness.

Have you ever had your maximum heart rate tested by a personal trainer when trying to estimate what intensity level you should be working out in? If so, it’s likely that the trainer used a formula called the Karvonen equation: 220- age in years. Once the maximum heart rate is determined, trainers typically choose a range of percentages they’d like you to stay in while working out to get optimal benefit from the exercise. Unfortunately, this formula is wildly inaccurate and using age-predicted maximal heart rate (APMHR) is not the best approach (Arena et al., 2016; Robergs & Landwehr, 2002). I was extremely humbled to learn this information as, sadly, this formula is included in the textbooks and exam prep materials in which trainers are required to read and get certified. It’s even included in the NSCA textbooks (Coburn & Malek, 2012; Haff & Triplett, 2016), which is an extremely credible and respectable organization. It’s something I had used in the past and it is alarming that this formula has been applied for decades without questioning or further investigation. Not only is this formula included in credible textbooks, but this is the same formula used by many large chain workout organizations including Orange Theory Fitness. Funny enough, one of my colleagues is working with one of the best runners in the world at this time and he was unable to get into the “orange zone” because his exercise capability far exceeded the abilities of the general population and the workout was not strenuous enough for him to get his heart rate up high enough. It is laughable because he felt inadequate during the class. It was only until he presented his data to my classmate that he realized it was because he was in too good of shape to get into the “orange zone”.

So, why is APMHR not considered accurate? First, this equation does not have original research to back it up but rather was derived from an attempt at the estimation of a linear regression to define data points (Robergs & Landwehr, 2002). Another reason that this equation is not suitable for figuring out maximum heart rate is that the magnitude of error with this equation is too large to be considered a valid measure (Arena et al., 2016; Robergs & Landwehr, 2002). Additionally, this equation (220-age) only takes into consideration a person’s age as a variable, whereas there are many other things to consider that could influence someone’s maximum heart rate (Robergs & Landwehr, 2002). Some things that may impact a client’s maximum heart rate include exercise mode and endurance training experience (Robergs & Landwehr, 2002). According to Nes et al. (2013), age alone was enough to adequately explain heart rate max and other factors including gender, self-reported physical activity, smoking status, VO2 max, and BMI did not have a significant interaction with determining heart rate max. However, this study included a general population and largely excluded elite athletes. Elite endurance athletes experience significant adaptive changes in the size, structure, and function of the heart (Thompson, 2007), which would likely affect their true maximum heart rate results.

In summary, the traditional 220 – age equation is inappropriate for estimating maximum heart rate. The current most accurate and accepted equation (205.8 –( 0.685x age)) still presents an unacceptably large error (6.4 beats/min) and there is presently no acceptable method of estimating heart rate max (Robergs & Landwehr, 2002). There is a need for further research on this topic as well as the development of a more appropriate method for determining heart rate max.

Until this research is done and a new method or equation has been developed, what is an acceptable way to determine if athletes are exercising at an appropriate intensity level? Methods such as subjective rate of perceived exhaustion (RPE) and the talk test (TT) have been suggested to be acceptable ways of ensuring an athlete is working at an intensity level that is high enough to achieve favorable adaptations from exercise such as VO2max and ventilator threshold improvements (Turek, Wargowsky, Cress, Doberstein, Hahn, Rysky, & Foster, 2018). However, for the general population, paying close attention to RPE or something like the talk test can be cumbersome and may shift their focus away from using safe form during exercise. In my practice, I push my clients to work hard but allow them some time to recover (typically 30 seconds-2 minutes, depending on the difficulty of the exercise that was just performed). I don’t use a specific formula for every exercise and every client when determining what exercise intensity they should be using. Not only is this cumbersome, but it’s not very feasible for my practice as everyone would have to wear a heart rate monitor or be testing their pulse after each exercise. For the general population, I encourage them to work as hard as they are capable of doing and make sure they keep moving/avoid long rest periods during their sessions with me. Even if a specific formula was said to be optimal for prescribing exercise intensity, everyone is different and unique situations may arise that could affect their ability to exercise at what would be considered an appropriate intensity. For example, if someone were to become pregnant or had a respiratory infection, then it would obviously limit the safety and their capability of being in a particular heart rate zone. By the way, if you are pregnant and exercising or if you may have underlying conditions that would require close attention to heart rate and intensity level, please, do not use this equation as a way of staying in your appropriate zone. I would definitely recommend the talk test or RPE in these cases at this time.

References

Arena, R., Myers, J., & Kaminsky, L. A. (2016, March). Revisiting age-predicted maximal heart rate: Can it be used as a valid measure of effort? American Heart Journal173, 49-56

Coburn, J. W., & Malek, M. H. (2012). NSCAs essentials of personal training(2nd ed.). Champaign (Illinois): Human Kinetics.

Haff, G., & Triplett, N. T. (2016). Essentials of strength training and conditioning (4th ed.). Champaign, IL: Human Kinetics

Nes, B. M., Janszky, I., Wisloff, U., Stoylen, A., & Karlsen, T. (2013). Age-predicted maximal heart rate in healthy subjects: The HUNT fitness study. Scandinavian Journal of Medicine & Science in Sports, 23(6), 697-704.

Robergs, R. A., & Landwehr, R. (2002). The surprising history of the “Hrmax=220-age” equation. Journal of Exercise Physiology Online, 5(2), 1-10.

Thompson, P. D. (2007). Cardiovascular adaptations to marathon running: The marathoner’s heart. Sports Medicine, 37(4-5), 444-447.

Turek, J., Wargowsky, A., Cress, M.L., Doberstein, S.T., Hahn, C.J., Rysky, A.L. & Foster, C. (2018). Comparison of the talk test and percent heart rate reserve for exercise prescription. Kinesiology, 50(1), 3-8.

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