Athletes frequently turn towards wearable fitness trackers for information regarding their performance and recovery. However, it has become clear over time that these tools are not perfect. In this post, we will discuss the more reliable data points these trackers measure, how you can use this data to improve your health or performance, and how being overly reliant on these devices can actually inhibit performance.
What are common metrics collected by activity trackers and how are they useful
The most common values measured by these devices include step counts, energy expenditure, heart rate, heart rate variability, and sleep.[1,2]
Step Counts: Measuring step counts is useful as it can be a good indicator of overall activity throughout the day. Walking an additional 1,000 steps per day shows significant decreases in risk of all cause mortality and cardiovascular disease.[3] In addition, having a target for the number of steps each day has been shown to help improve participation in physical activity.3 If measuring step counts is an important number for you, Apple Watches and Fitbit devices have been identified as being the most accurate when compared to other brands like Garmin and Nike.[1] However, it is important to remember that performing upper body exercise can alter step counts and result in some degree of inaccuracy among all of these devices.
Energy Expenditure: On the surface, energy expenditure may seem like a very useful measurement provided by various devices. This is especially true if you are attempting to match caloric intake with your activity level. However, none of the major brands of commercially available activity trackers have demonstrated sufficient accuracy in assessing energy expenditure.[1,4] Therefore, it is best to use other values or tools available when measuring your activity level and dietary needs.
Heart Rate: Resting heart rate is a valuable metric for assessing health.[5] Having a lower resting heart rate is generally associated with improved cardiovascular wellness and can be observed over time to track progress. Heart rate during activity can be used to measure the intensity of exercise when combined with other formulas or compared to an individual’s maximum heart rate.[1] Garmin devices and Apple Watches were found to be the most accurate at measuring heart rate.[1]
Heart Rate Variability: Similar to heart rate measurements, heart rate variability (HRV) can also be used to assess overall cardiovascular health.[6] In addition, HRV is a strong indicator of the body’s response to stress.[6] Therefore, HRV can be used to assess an individual’s response to training and approximate their recovery afterwards.[6] Unfortunately, there are limitations to this application as recovery is a more complex process than what can be determined by a simple calculation of HRV. For example, HRV is not as accurate of an indicator for those who mainly participate in strength sports. The exact reason for this is still unknown. However, HRV may not be as valuable for assessing recovery after a strength workout due to the fact that the muscular and cardiovascular systems return to baseline relatively quickly following strength training while fatigue to the nervous system may remain. Since HRV is derived from values of heart rate, brands such as Garmin or Apple will tend to provide the most reliable data for determining HRV.
Sleep: Sleep is one of the best tools available to us when it comes to maximizing recovery. Many fitness trackers will assess sleep duration and can even provide values to attempt to determine the quality of sleep. Unfortunately, the majority of commercially available devices are not able to consistently provide an accurate analysis of sleep. Therefore, this type of information from a device should not be the sole rationale for altering training or lifestyle.[7]
When data can be detrimental
Usually having more information available is beneficial. However, how we respond to some of the information can ultimately have a negative effect on performance. For example, individuals who received a poor sleep score in a study demonstrated worse performance compared to those who received high sleep scores even though these scores had been assigned randomly and were not based on any actual analysis of how the individual slept.8 It is important to remember that the devices we use are not entirely accurate with metrics such as sleep, energy expenditure, and recovery. With this in mind, we should be careful not to let the data we receive from our devices influence our perceptions as this could negatively impact performance.
Conclusion
The technology available to us can be valuable tools to help us maximize our health and performance. These devices can provide metrics that we can use to assess overall health, exercise intensity, and approximate our level of recovery between sessions. While many of these trackers are accurate for some measurements such as step counts, heart rate and HRV, these numbers may not always tell the whole story. At the end of the day, these devices may help guide us but should not dictate our decisions.
References:
Germini F, Noronha N, Borg Debono V, et al. Accuracy and Acceptability of Wrist-Wearable Activity-Tracking Devices: Systematic Review of the Literature. J Med Internet Res. 2022;24(1):e30791. Published 2022 Jan 21. doi:10.2196/30791
Robbins R, Seixas A, Masters LW, et al. Sleep tracking: A systematic review of the research using commercially available technology. Curr Sleep Med Rep. 2019;5(3):156-163. doi:10.1007/s40675-019-00150-1
Hall KS, Hyde ET, Bassett DR, Carlson SA, Carnethon MR, Ekelund U, Evenson KR, Galuska DA, Kraus WE, Lee IM, Matthews CE, Omura JD, Paluch AE, Thomas WI, Fulton JE. Systematic review of the prospective association of daily step counts with risk of mortality, cardiovascular disease, and dysglycemia. Int J Behav Nutr Phys Act. 2020 Jun 20;17(1):78. doi: 10.1186/s12966-020-00978-9. PMID: 32563261; PMCID: PMC7305604.
Hall KS, Hyde ET, Bassett DR, Carlson SA, Carnethon MR, Ekelund U, Evenson KR, Galuska DA, Kraus WE, Lee IM, Matthews CE, Omura JD, Paluch AE, Thomas WI, Fulton JE. Systematic review of the prospective association of daily step counts with risk of mortality, cardiovascular disease, and dysglycemia. Int J Behav Nutr Phys Act. 2020 Jun 20;17(1):78. doi: 10.1186/s12966-020-00978-9. PMID: 32563261; PMCID: PMC7305604.
Jensen MT. Resting heart rate and relation to disease and longevity: past, present and future. Scand J Clin Lab Invest. 2019 Feb-Apr;79(1-2):108-116. doi: 10.1080/00365513.2019.1566567. Epub 2019 Feb 14. PMID: 30761923.
Dong JG. The role of heart rate variability in sports physiology. Exp Ther Med. 2016;11(5):1531-1536. doi:10.3892/etm.2016.3104
Thamm A, Freitag N, Figueiredo P, et al. Can Heart Rate Variability Determine Recovery Following Distinct Strength Loadings? A Randomized Cross-Over Trial. Int J Environ Res Public Health. 2019;16(22):4353. Published 2019 Nov 7. doi:10.3390/ijerph16224353
Draganich C, Erdal K. Placebo sleep affects cognitive functioning. J Exp Psychol Learn Mem Cogn. 2014 May;40(3):857-64. doi: 10.1037/a0035546. Epub 2014 Jan 13. PMID: 24417326.
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