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Unpacking the Science of Thresholds, VO2max, and Max Heart Rate

Guest Author Kristen Hench, Ph.D., USAT Certified Coach. If you're interested in contributing to our blog, reach out to us at

Cardiorespiratory fitness, typically determined by maximal oxygen uptake (VO2max), is an essential measurement for the exercise physiologist, coaches, athletes, and other health professionals. Our cardio-respiratory system is an incredible machine that can adapt to help an athlete perform stronger, faster, and more efficiently. When an athlete improves their endurance, the body adapts to supply more oxygen-rich blood to the working muscles that in turn become more adept at pulling and utilizing oxygen from the bloodstream. According to the American Heart Association, the capacity of an individual's cardiorespiratory fitness has been viewed as the best indicator of a person's overall health. The intensity at which one trains is arguably one of the most critical components when it comes to prescribing exercise in order to improve fitness (Wolpern, Burgos, Janot, & Dalleck, 2015).  


What is VO2max, VT1, and VT2?

At VO2max the athlete is at a 9 out of 10 on the perceived effort level scale. It is the maximum capacity of the body to breathe in, transport, and use oxygen during exercise (work) and reflects a person’s cardiorespiratory fitness. A deconditioned athlete has a lower VO2max than someone who is conditioned. As an athlete becomes more conditioned, their VO2max will increase. Before reaching VO2max, an athlete will go through the first ventilatory threshold (VT1) and the second ventilatory threshold (VT2).

When an athlete passes VT1 they are at an effort level associated with 3 out of 10. The intensity can be observed by elevated but comfortable breathing, and despite an increase in overall lactate production and associated by-products the body is able to clear it as quickly as it is produced. At this point, the athlete is breathing comfortably and could hold a conversation. As the intensity of the exercise increases towards VT2, breathing begins to rise to the point where they can no longer comfortably talk while exercising.

When an athlete passes VT2 they are at an effort level associated with 7 out of 10. As the effort level increases above VT2, breathing and lactate will increase exponentially. Due to the high rate of breathing, the athlete can only string a couple of words together at a time. At this point, the duration of exercise decreases due to the intensity level. VT2 is also known as the anaerobic threshold (AT).

A less conditioned athlete will reach VT1, VT2, and VO2max at a lower intensity of exercise than a more conditioned athlete. For example, an extremely deconditioned person may arrive at his or her VT1 while just walking while a conditioned athlete will reach it at a moderate running pace.

What is Max Heart Rate?

For many years exercise intensity has been measured using heart rate. The maximum heart rate (HRmax) for an individual was used to make specific exercise-intensity recommendations. More recent research has shown that formulas relying on Heart Rate to prescribe an individual's effort zones have an error margin of 29% (Myers et al, 1999). The reason for this inaccuracy is due to the fact that an individual’s HRmax, whether measured in a test or calculated from an age-based formula, is governed by more than just his or her age or fitness level.

Why is using VT1 and VT2 more accurate in measuring exercise intensity?

By knowing where the true intensity markers of VT1, VT2, and VO2max are, a coach and athlete can develop tailored training progressions based on the individual athletes' response. Working above resting levels but below VT1 is a safe way to build fitness in deconditioned athletes and is key to increasing fat utilization for all fitness levels. This improves our overall running economy by increasing the intensity level at which our bodies begin to rely on our limited carbohydrate supply for fuel. Working at and slightly above VT2 helps maximize the body's ability to create and clear lactate which translates to our ability to go faster for longer. Targeting VO2max during short and intense intervals trains the body to utilize a greater amount of oxygen, thereby raising the ceiling of our fitness potential. Combining these effort levels in the right way and the right duration throughout a training cycle results in optimal improvement for the least amount of work. 


Blair, S. N., Kampert, J. B., Kohl, H. W., Barlow, C. E., Macera, C. A., & Paffenbarger, R. S. (1998). Influences of cardiorespiratory fitness and other precursors on cardiovascular disease and all-cause mortality in men and women. Journal of American Medical Association, 30(6), 899-905.

Meyer, T, Gabriel, HH, Kindermann, W. (1999) Is determination of exercise intensities as percentages of VO2max or HRmax adequate? Medicine & Science in Sports & Exercise, Volume 31, Issue 9, 1342-1354.

Wolpern, A. E., Burgos, D. J., Janot, J. M., & Dalleck, L. C. (2015). Is a threshold-based model a superior method to the relative percent concept for establishing individual exercise intensity? A randomized controlled trial. BMC Sports Science, Medicine, and Rehabilitation, 7(16), 1-9.

Kristen Hench

Kristen Hench, Ph.D., is a certified coach through USAT, USAT Para, ACE, USAC, ASCA, ASFA Yoga certified, and is a RRCA certified race director. She has trained beginner through elite athletes helping many to reach podium finishes as well as meet their personal goals in triathlon, running, track, and swimming. Kristen coaches adaptive sports with the USAF AFW2 program as a cycling coach and also works with a variety of able-body and parasport athletes through TRIMotion3. She enjoys helping children and youth get healthy, learn new life-long skills, and build confidence. She has coached internationally and was selected to coach in the 2018 and 2020 Invictus games. Kristen has also directed numerous family races and competed in several triathlons herself, including the Ironman distance events. She placed in the top three for her age group in the inaugural year of the Mountaineer Half Ironman and was one of the top swimmers in the 2004 Lake Placid Ironman. Besides triathlons, Kristen also enjoys marathons (with a PR of 3:15), triathlon, swimming, and a multitude of boot camp activities.