Measuring Physiological Parameters of Stress and Recovery

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In order to push our limits and increase our capacity without overwhelming ourselves, it is important to be able to identify the impact on our biology and our ability to recover.

The previous article discussed, in part, the importance of intentionally pushing our physical and psychological limits in order to increase our capacity and ability to be at our best under progressively more challenging situations.  From this understanding, the ensuing consideration becomes how best to determine whether we are pushing our limits appropriately or whether we are doing so to excess.  One method by which to answer this question is the subjective feelings we experience.  This is inherently challenging because our ability to maintain allostasis and avoid allostatic load can vary over time and across different situations.  In addition, because it is inherently subjective and, while important, would be benefited through supplementation with objective information.

There are two important considerations when evaluating the magnitude of allostasis to which we expose ourselves.  This can be viewed as the change in our biology during the event itself and our ability to recover following the scenario.  As alluded to above, our subjective experience both during and following these situations is important to acknowledge and factor into our analysis of the extent to which the challenge was appropriate and not overwhelming.  

In addition, objective physiological metrics can provide important information to include in our analysis.  As discussed in previous articles, one of the best and currently commonly utilized metrics for assessment of the degree of biological stress and recovery is heart rate variability (HRV).  This is a measure of the time between heart beats and in this paradigm reflects the balance between sympathetic nervous system activation and ventral vagal tone.  While other factors influence HRV, this understanding can be simplified as the greater the sympathetic activation, the less will be our HRV and the greater our ventral vagal activation, the greater will be our HRV.

It is important to emphasize that the process of increasing our capacity and ability to tolerate greater demands while being able to be at our best requires intentional and deliberate training.  It also requires that following such training, we are able to recover back to baseline and restore homeostasis.  By following this paradigm, we are able to increase our capacity to tolerate greater degrees of demand and recover more effectively so as to be prepared for upcoming situations.  Ultimately, this is required if we are to pursue our best in any and all areas of life, which inherently necessitates progressing our abilities and capacity. 

In order to accomplish this with as much fidelity as possible, it is to our advantage to incorporate measurement of pertinent metrics into our intentional and deliberate training as well as our daily lives.  This should be done in addition to and as a compliment to acknowledging our subjective assessment of our stress and recovery.  The most commonly measured metrics are heart rate and HRV and these can be determined for this purpose using wearable technologic devices.  Some are worn continuously and others on a semi-regular basis.  Some devices provide continuous measurement of HRV and others provide an average HRV over a period of time, typically while asleep.  There are relative advantages and drawbacks to each type of device and the optimal one for a given individual is dependent upon their specific goals, strengths, and areas for improvement.  From my perspective, the inclusion of a device which includes continuous measurement of HRV is important since insights can be lost when the HRV data is averaged over a duration of time.

Seipajarvi et al (2022) studied the application of a wearable device, typically utilized on a semi-regular basis, comprised of a single lead ECG for measurement of heart rate and HRV.  They also utilized the HRV data to calculate an index to provide a measurement of the stress-relaxation balance.  They compared this data to measurements of salivary cortisol, which is a direct indicator of activation of the hypothalamic-pituitary axis in response to stress, and self-reported perception of stress.  They included 63 healthy adults between the ages of 18 and 30, 61 healthy adults between 45 and 64, and 73 adult patients with either hypertension or diabetes.  They administered a standardized psychosocial stress test and measured heart rate and HRV continuously over three days as well as obtaining regular measurements of salivary cortisol and perceived stress.  Amongst each group there was a decrease in HRV during the stress task.  There was increased salivary cortisol during stress amongst the patient group and the healthy adult group between 45 and 64 years of age.  Following the stress event, each group demonstrated decreased cortisol.  The HRV based stress-relaxation index was associated with physiological stress across the study.

The data provided by the study leads to several important insights that can be applied to the discussion related to measurement of stress and recovery.  As a proof of concept, the data provides evidence regarding the ability to measure HRV and develop an index based upon these metrics for evaluating stress-recovery balance using a wearable technologic device.  The benefit of continuous measurement of HRV in comparison to an average metric over a period of time, such as during sleep, is demonstrated as there can be additional insights observed through the dynamic and continuous changes in HRV in response to changes in events and situations.  The study also provides evidence regarding the validity of wearable devices to measure HRV and determine an index of stress-recovery balance across different ages and amongst individuals with hypertension or diabetes.

The evidence provided by the study forms a basis of a component of the Practices of the Healthcare Athleterelated to the integration of technology to give insights into these metrics.  The data provided regarding these physiological measures are used to identify the baseline state prior to beginning training of skills and strategies, to measure the change over time in response to implementation of these skills and strategies, as well as to adjust training in response to the metrics.  In addition, for those using these devices on a continuous basis, it may be possible to adjust some daily activities in response to the HRV metrics and related stress-relaxation balance.

In the pursuit of health, wellbeing, and sustainable high performance within the polyvagal informed Practices of the Healthcare Athlete, the integration of objective data in association with perception of stress and recovery are key elements.  In order to be able to pursue our best, it is necessary to push the limits of our capacity and, just as importantly, recover to homeostasis following such events and situations.  In order to do this in as controlled a fashion as possible, thereby limiting allostatic load, the integration of physiological metrics is indispensable.

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Seipajarvi SM, Tuomola A, Juurakko J, Rottensteiner M, Rissanen A-P, Kurkela JLO, Kujala UM, Laukkanen JA, Wikgren J.  Measuring Psychosocial Stress with Heart Rate Variability-Based Methods in Different Health and Age Groups.  Physiol Meas 43 (2022): 055002.

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