Is a 60 second HRV measurement sufficient for valid assessment?

When I first moved out to Auburn to work on some HRV projects, I fully expected to jump right into some training study’s where we’d have team’s use an HRV app and start collecting data. I realized pretty quickly that these projects would probably have a hard time making it through the review process with a journal without validation of the field devices and the modified recording methodology that they utilize. Our first projects were therefore to cross-validate an HRV app that we could use with the athletes (link to study), assess the agreement between the ultra-short measurement duration typically used by app’s, and determine how long it took for an athlete to achieve a physiologically stable condition prior to recording HRV.

In our latest project we recorded 5 minute ECG’s from 23 collegiate male athletes (from the Soccer and Basketball teams) at rest and following a maximal graded exercise test. 5 minutes has been established as the standard for short-term HRV assessment. However, for lnRMSSD (the value used by the smart phone app’s like ithlete and BioForce), there is evidence suggesting that ultra-short measures (60 seconds or less) may be sufficient. From the 5 minute ECG’s, we randomly selected 10, 30 and 60 second segments to compare to the 5 minute lnRMSSD values. Essentially, we found that 60 second measures showed near perfect agreement with the 5 minute measures both at rest and post-exercise. However, as might be suspected, as measurement duration decreased (to 30 and 10 seconds), the agreement with the 5 minute measures also decreased. The key points of the study are listed below.

key points ultra short

 

Our results make us quite confident that 60 seconds is sufficient for valid HRV assessment in athletes. The full text for this study is linked below.

Ultra-Short-Term Heart Rate Variability Indexes at Rest and Post-Exercise in Athletes: Evaluating the Agreement with Accepted Recommendations

Our latest project, currently in the process of being submitted for review, assesses how long the pre-recording resting period needs to be for “stabilization” prior to an HRV recording. One of our primary goals is to determine the shortest valid recording methodology possible to enhance convenience of HRV monitoring in field settings. Next is to determine how this can be practically applied in the sports field for training management as there is very little longitudinal data from team sport settings reported in the literature. We hope that the shorter measurement protocols and validity of field tools will encourage more work in this area.

HRV Recording Methodology: Stabilization

Smart phone app’s and other field tools have made HRV data collection relatively simple and affordable for coaches, athletes and recreational lifters. However, the shortened recording methodology utilized by these devices requires validation. Standardized guidelines recommend that short-term (i.e., 5-min) HRV be collected under physiologically stable conditions (Task Force). Most HRV papers will allow for 5 minutes or greater of supine rest prior to HRV recording to allow for stabilization. However, this 5+ minute pre-recording period is not practical for daily monitoring. A 1 – 2 minute HRV recording period with a very minimal stabilization period used by many app’s is still too long for some individuals to comply with daily measures.

The issue of “stabilization” was the topic of our latest research project that we just presented at the ACSM Annual Meeting in Orlando this past weekend. We looked at the time-course for stabilization of HRV across 5-min ECG segments (e.g., 0-5 min, 1-6 min, 2-7 min, 3-8 min, etc.)  in 12 endurance athletes (6 female) and 12 non-athletes (6 female). We included lnHFnu, lnLFnu, and lnRMSSD.

The figures from the poster are displayed below (Athletes on left)

Stab Poster title

stability figures

 

The full manuscript for this project (with a different methodological approach) is currently in review so I will not get into too much depth on the discussion of the results. However, it is quite clear that lnRMSSD demonstrates the most and earliest stability of the 3 HRV parameters. Therefore, for lnRMSSD assessment, a minimal stabilization period is likely a non-issue. When including spectral measures (e.g., HF, LF), a longer period for stabilization may be required, though lnHFnu was relatively stable in the athletic group in the current sample.