Unpacking the Science of Thresholds, VO2Max, and Max Heart Rate

Guest Author Kristen Hench, Ph.D., USAT Certified Coach, has the scientific and personal background to be an authority on this piece, and we're glad to feature her. If you're interested in contributing to our blog, reach out to us at support@tymewear.com.

Cardiorespiratory fitness, typically determined by maximal oxygen uptake (VO2max), is an essential measurement for the exercise physiologist, coaches, athletes, and other health professionals. The human heart is a machine that can adapt to help an athlete perform stronger, faster, and more efficient. When an athlete improves their endurance, their 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?

VO2 max refers to the maximum volume of oxygen an athlete’s body can use during exercise. 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 VO2 max than someone who is conditioned. As an athlete becomes more conditioned, their VO2 max will increase.  Before reaching VO2 max, an athlete will go through the first ventilatory threshold (VT1) and the second ventilatory threshold (VT2).  

When an athlete reaches VT1, his or her intensity can be observed by elevated breathing and accumulation of blood lactate. At this point, the athlete is breathing comfortably and could hold a conversation. As the intensity of the exercise increases, breathing begins to rise to the point where they can no longer comfortably talk while exercising.

When an athlete reaches VT2, breathing and lactate 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 VO2 max 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 more conditioned athlete will reach these markers at a moderate running pace.

What is Max Heart Rate?

For many years exercise intensity was measured mainly using heart rate. The maximum heart rate (HRmax) for an individual was measured using a relatively inaccurate formula that made specific exercise-intensity recommendations. Using any formula that begins with age presents a challenge and introduces a vast potential for a range of errors. For example, not every 30-year-old endurance athlete has the same fitness level, and an individual’s HRmax rate is governed by more than just his or her age.

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

Today, instead of relying on formulas, specific field tests or instruments like Tyme Wear, measure precise points where the physiological response to exercise intensity shifts. Through understanding the two intensity shifts at VT1 and VT2, a coach and athlete can develop more tailored training progressions because they are based on the individual athletes' response and not formulas. Working above resting levels but below VT1 will improve fitness in deconditioned athletes and maintain it in those with an average baseline level of fitness. Working between VT1 and VT2 will maximize both caloric quality and caloric efficiency in the interest of prioritizing a metabolic response during the exercise session. Working above VT2 will maximize increases in the ability to perform at a high level and prioritizes a metabolic response both during and after the exercise session. Combining these effort levels in an optimal way 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. https://doi.org/10.1097/00005768-199806000-00019

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. https://doi.org/10.1186/s13102-015-0011-z

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.

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