How accurate is your Garmin’s VO2max estimate?

Traveling along the trails, sidewalks, and main streets of the towns they reside in, runners, cyclists, and endurance sports athletes everywhere all know a familiar sound. The delightfully gratifying chirp of a fitness tracker as you complete your next mile, achieve a new PR (personal record), or record a new VO2max.

Ever since I entered the world of endurance sports training eight years ago, I’ve heard athletes talking about their VO2 max, how to improve it, and how accurate (or not?) fitness trackers are at actually measuring these values.

I decided to explore the technology of Garmin fitness watches to understand how VO2max is calculated and do a baseline comparison of how these wearable technologies VO2max predictions compare to laboratory testing.

Firstbeat Technology’s Fitness Test is used by Garmin and other fitness companies to calculate VO2max for a variety of different activities. Described in patent US20110040193A1, this Fitness Test calculates users’ VO2 in the following steps:

1) The personal background info (at least age) is logged
2) The person starts to exercise with a device that measures heart rate and speed
3) The activity collected data is segmented to different heart rate ranges based off the persons background info and the reliability of different data segments is calculated(reliability is measured based off how continuous the activity is- uninterrupted segments are better than those where the user has to stop)
4) The most reliable data segments are used for estimating the person’s aerobic fitness level (VO2max) by utilizing the person’s heart rate and speed data

Speed data from reliable segments are used to calculate a VO2, oxygen consumption, during that segment. 20-30s bouts are used to calculate VO2 across segments using one of the following theoretical VO2 calculations:

Walking and Pole Walking: Theoretical VO2 (ml/kg/min)=1.78*speed*16.67[tan(inclination)+0.073]
Running on a Level Ground: Theoretical VO2 (ml/kg/min)=3.5 speed
Running in a Hilly Terrain: Theoretical VO2 (ml/kg/min)=3.33*speed+15*tan(inclination)*speed+3.5
Cycling: Theoretical VO2 (ml/kg/min)=(12.35*Power+300)/person’s weight
Rowing (Indoor): Theoretical  VO2 (ml/kg/min)=(14.72*Power+250.39)/person’s weight                                Unit of speed=kilometers per hour (km/h) 
Unit of inclination=degrees)(°) 
Unit of power=watts (W) 
Unit of weight=kilograms (kg)

From these calculated theoretical VO2 values, heart rate information is used to determine effort of segments. Heart rate zones based on user information are utilized to evaluate effort, and then effort is used to determine that VO2 as a %VO2max. VO2max estimates are made for each segment using %VO2max. These segment VO2max can be weighted based off heart beat derived parameters and performance parameters, and then used to calculate VO2max.[1]

An affordable mode of tracking your VO2max through measuring heart rate and speed data – pretty neat, right? But how accurate is this technology and how does it match up to laboratory testing?

Firstbeat conducted their own study to validate the technology and its effectiveness at estimating VO2max. They found that “[t]he accuracy of the method when applied for running is 95% (Mean absolute percentageerror, MAPE ~5%), based on a database of 2690 freely performed runs from 79 runners whose VO2max was tested four times during their 6-9 -month preparation period for a marathon”(4). Error in estimated VO2max was less 3.5ml/kg/min in most cases, which is fairly accurate considering most submaximal testing has an error of 10-15%. Method accuracy varied with respect to estimated maximum heart rate(HRmax). ” If the HRmax is estimated 15 beats/min too low, the error in the VO2max result is about 9%. Respectively, if the HRmax is estimated 15 beats/min too high, the error in VO2max result is 7%. If the person’s real HRmax is known, the VO2max assessment error falls to the 5% level”(5). This study suggests a high degree of accuracy for Firstbeat’s fitness test technology in predicting VO2max.[2]

A group of scientists at Southern Illinois University Edwardsville evaluated the wearable technology’s accuracy by conducting a laboratory VO2max test on male and female runners, then allowing participants to use the wearable technology to calculate VO2max in a 10 minute self guided run. They found that the Garmin Forerunner 230MAX and 235MAX measured VO2max within -0.3 ± 3.4 ml/kg/min, p=0.02 for the 230MAX and -1.1 ± 4.0 ml/kg/min, p=0.026 for the 235MAX for female runners, and -1.1 ± 3.4 ml/kg/min, p=0.149 for the 230MAX and -3.2 ± 4.2 ml/kg/min, p=0.002 for the 235MAX for male runners. There is a greater amount of variability in the male group; however, this could be due to miscalculations in HRmax and potential variations in levels of effort in participant during the 10 minute self guided run. Although there is greater variability within the male group, the devices still appear fairly accurate at predicting VO2max.[3]

Wearable conducted an evaluation of their own putting fitness watches to the test – assessing the accuracy of Garmin, Fitbit, and Jabra devices in measuring VO2max. They found that Garmin technology provided a VO2max estimation within 0.3 ml/kg/min of their study participant, which was the most accurate of all devices tested. The high degree of accuracy found in their study remains consistent with other larger scientific studies.[4]

Across the board, there appears to be a high degree of accuracy with Firstbeat’s Fitness Test in estimating VO2max. For endurance athletes everywhere, this is a huge sigh of relief. Rather than partaking in expensive, strenuous VO2max testing, we can monitor our progress utilizing the technology in the watches we wear everyday. In addition to watching our paces, heart rates, and overall progress, we can also monitor our cardiovascular health and athletic progress as we continue to train and push ourselves everyday.


[1]Seppanen, M., Pulkkenin, A., Kurunmaki, V., Saalasti, S., & Kettunen, J. (2016). U.S. Patent No. US20110040193A1. Washington, DC: U.S. Patent and Trademark Office

[2] Firstbeat Technology(2014). Automated Fitness Level (VO2max) Estimation with Heart Rate and Speed Data.

[3]Snyder, N. C. , Willoughby, C. A. & Smith, B. K. (2017). Accuracy of Garmin and Polar Smart Watches to Predict VO2max. Medicine & Science in Sports & Exercise, 49(5S), 761. doi: 10.1249/01.mss.0000519024.10358.0b.

[4]Stables, J., & Stables, J. (2016, December 21). The big ​VO2 Max test: Fitbit, Garmin and Jabra go head-to-head. Retrieved from


Can You Beet The Competition With Nitrate Supplements?

Nitric Oxide (NO) is a supplement currently used by many athletes because it is a known vasodilator, which can increase blood flow, mitochondrial efficiency, and contractility of muscles. While there are a few different kinds of nitrate supplements, the most common comes in the form of beetroot juice. When ingested, the nitric oxide is easily broken down into nitrate, which can be used by the body to help increase efficiency of exercise. Multiple studies have been done regarding the effect of beetroot juice supplementation in both trained and untrained athletes; as well as by acute or long term dosing. Due to the nature of NO in exercise, it is generally used to supplement endurance activities, with only a few studies looking at shorter length, or strength exercise. Currently, there is data to suggest that beetroot juice has a more noticeable effect in untrained individuals than in trained athletes, which is not surprising. The trend normally seen in these studies is that acute doses of beetroot juice will lower VO2 during submaximal exercise, allowing individuals to exercise more efficiently. Another effect of nitrate is the increase in mitochondrial efficiency. This effect was tested through long term studies regarding beetroot juice supplementation. In low-moderately trained athletes it was also found that VO2 decreased at submaximal exercise, similar to acute dosing. Additionally, exercise tolerance was also increased by up to 16% after one week of supplementation. While this may be due to the effects of training it was a significant difference. In highly trained athletes, it was found that beetroot juice increased workload and reduced energy cost at exercise intensity. However, the variability in performance could have been the cause of this as noted by the authors of the study. Overall, while there is some evidence to support the use of beetroot juice as an ergonomic aid, there is also a large amount of data to suggest that it has very little to no effect of athletic performance.

Table of studies done to research the effects of acute nitrate supplementation in elite athletes

This topic relates to class in that it aims to determine what affect different training methods/supplements have on athletic performance. It seems that there are potential benefits to using beetroot juice or other nitrate supplements as a training tool in both acute and long-term doses. One of the issues seems to be in determining the proper dosage of beetroot juice. There were multiple studies where no benefit was seen with small doses and significant benefits were seen with a higher dose. Determining this value will be important in future studies to ensure that possible benefits are not being overlooked. Additionally, larger studies should be conducted as only one study referenced in the article had more than 20 subjects. This could be a potential major limitation given the large amount of variability in and between different athletes and sports. NO supplements also would seem to be more beneficial to endurance athletes than it would be to strength athletes during training. While there is only a small amount of evidence to support the claim that beetroot juice will improve athletic performance, there is no data to suggest that taking this supplement will have negative effects on performance so trying it in your next training cycle may be worth it.



References                                                                                                                         Andreas Zafeiridis. The Effects of Dietary Nitrate (Beetroot Juice) Supplementation on Exercise Performance: A Review. American Journal of Sports Science. Vol. 2, No. 4, 2014, pp. 97-110. doi: 10.11648/j.ajss.20140204.15

Muscle Stretch Shortening in Upper Extremity Explosiveness

After talking briefly about muscle stretch shortening in class, I thought this was an interesting topic and looked into some literature to better understand what is going on. I found a study that focused on upper-body explosive movements, and how load and stretch shortening cycles (SSC) affect the kinematics, kinetics, and muscle activation that occur. This was an interesting study because they looked at maximal effort bench throws, where much of the previous research focused only on lower-extremity exercises. Each subject performed an SSC throw and concentric only throws, comparing displacement, velocity, acceleration, force, power output and EMG from the pectoralis major, anterior deltoid, and triceps brachii. SSCs are usually performed before explosive movements (e.g. throwing, jumping) which lengthen the muscle preparing to contract to ensure maximal velocity is reached during the movement. When the muscle lengthens, elastic energy is stored which can then be released during the movement, however, if the time between lengthening and contracting is too long, the energy dissipates, leading to a slower contraction with less power.

As expected, the average velocity was lower for the concentric only throws when compared to the SSC throws, however, there was no difference in throw height between the two groups. Average and peak force and power output were both higher for the SSC through compared to the concentric only throw. The findings from this study agree with findings from previous studies focusing on vertical jump, showing that similar muscle kinetics are at play. Muscle kinetics are an extremely interesting area of study, and even though we only briefly discussed muscle length-tension, force-velocity, and power relationships in class, this is a huge field of study. Some groups choose to look at specific muscle groups, while others look at more complex movements that require multiple groups of muscles to be activated. This area of research has led to improvements in stretching suggestions for athletes; stretching before performing explosive movements is not actually as beneficial as we once thought. Stretching the muscle allows for elastic energy dissipation, instead of storing the energy for immediate release. However, stretching is still extremely beneficial after workouts, helping to prevent muscle soreness and excess inflammation. Additionally, there are some chronic adaptations to stretching including increasing flexibility for a wider range of motion during typical daily activities as well as athletic endeavors.


  1. Newton, R. U., Murphy, A. J., Humphries, B. J., Wilson, G. J., Kraemer, W. J., & Häkkinen, K. (1997). Influence of load and stretch shortening cycle on the kinematics, kinetics and muscle activation that occurs during explosive upper-body movements. European Journal of Applied Physiology and Occupational Physiology, 75(4), 333–342.
  2. Bosco, Carmelo, and Paavo V. Komi. (1979) Mechanical characteristics and fiber composition of human leg extensor muscles. European journal of applied physiology and occupational physiology4 (1979): 275-284.

Different ways to measure VO2max

After recently observed a VO2max test in class, I began wondering more about this type of measurement of maximal oxygen uptake. Is there a better, less exhausting way to measure metabolic limits and aerobic power? How do you measure VO2max in patients with paralysis? Is VO2max even useful to measure in impaired patients? I started looking into different ways to measure VO2max and found an interesting paper from 1980 (Epstein et al, A comparison of various methods for the determination of VO2max, Eur J Appl Physiol Occup Physiol). Although this paper is relatively old, it is still being cited today and remains relevant. In this study, four different methods were used to determine VO2max including direct measurements using uphill treadmill running, cycling on an ergometer, and a step test, and indirect measurements using the Astrand-Rhyming procedure of predicting VO2max. The subjects were non-professional sportsmen, so the conclusions of this study can be applied to non-professional athletes, unlike a lot of the previous articles we have discussed in class that only applied to college-level or professional athletes.

Looking at Table 2, we can see that VO2max was highest when measured using the uphill treadmill test, in agreement with previous results. Interestingly, this method did not have a significantly higher heart rate, indicating that it may not be the most strenuous method. Additionally, the O2 pulse, a measure of cardiac performance, was consistent across the three direct measurement methods. These discrepancies have been attributed to differences in subject motivation or involvement of a varying volume of muscles necessary to perform each method. Even so, the methods in this study did not generate significantly different measures of VO2max, so we can conclude that any of the four methods tested here will adequately determine VO2max.