Heart Rate Variability (HRV) and Psychological Stress

All stress matters

I’ve recently come across two cases in which HRV data was tracking very well with psychological stress in athletes I coach, and I’d like to show in this blog how effective the data can be, and how we can use it to make meaningful adjustments that will benefit our long-term health and performance.

Let’s start with the basics.

HRV and (psychological) stress

For this section, much of the credit goes to Emma Mosley and Sylvain Laborde, with whom I am writing a book, together with Dan Plews as well, and who have taught me a lot about psychological stress and HRV.

HRV has become one of the most widely used physiological markers to assess stress, but it is often misunderstood. We tend to think of HRV as if it were measuring stress directly, when in reality HRV is reflecting the regulation of the autonomic nervous system. This means that HRV - when measured at the right time - captures how our body adapts to and recovers from stressors, not the stressor itself. When HRV is higher, it signals a stronger parasympathetic influence and greater capacity in response to challenges. When HRV is reduced, it may indicate that we are mobilizing resources to meet demands, or that chronic strain has accumulated to the point where recovery is impaired. Context always matters.

When we talk about psychological stress, we are talking about situations in which we perceive that demands outweigh our resources. This is not just a matter of workload or hours in the day; it is a deeply subjective process. Two individuals facing the same task can respond very differently, one seeing it as an opportunity, the other as a threat. Stress is always biopsychosocial, touching the body, the mind, and the way we relate to others. This is why HRV data must always be placed within the wider narrative of someone’s context.

The autonomic nervous system is central to this process. At rest, parasympathetic activity helps maintain a state of balance and flexibility. When we face a stressor, parasympathetic activity is withdrawn, and sympathetic drive increases to mobilize energy. HRV reflects this dynamic, not by directly capturing sympathetic activity but by indexing parasympathetic modulation. Lower HRV in the moment of stress does not mean something bad has happened. It means that the body is responding, that resources are being mobilized. What matters is how quickly and effectively the system returns to baseline.

Daily HRV measurements can therefore become a tool for stress assessment and management. By looking at how values fluctuate daily, we can identify acute responses, such as a drop after a poor night of sleep or a tough interval session, and we can identify chronic trends, such as persistently suppressed values that do not rebound.

In these cases, HRV provides a prompt for reflection: are we getting enough sleep, are we fueling adequately, are there emotional or social stressors that we need to address? Can we do anything about it? If not, what other stressors could we modulate? As our capacity to handle stress is limited (we can only take so much), training becomes a good candidate if we want to reduce stress to allow for more capacity to manage psychological stressors.

As a coach, I find HRV data particularly useful when combined with an athlete’s subjective feel, as we do in the HRV4Training questionnaire, as this gives me a strong signal that something is going on, and it might be a good idea to implement some changes. There is no replacement for a good subjective assessment of how you feel - no toy can (or should) do that for you.

Let’s see two case studies below.

Case studies

Below is the data from an athlete I coach who has recently experienced more psychological stress, some unrelated to training itself (travel, moving, etc.), and some somewhat related but not in the way we normally think (i.e. not a hard workout, but the transport to a future race for which we had trained several months, getting canceled without feasible alternatives). The result was a strong suppression leading to the baseline HRV ending up below the normal range:

During this week, training load was low and motivation was pretty low too:

The two (HRV and motivation) correlated quite strongly in terms of chronic (i.e., baseline) changes, as shown in HRV4Training Pro:

In terms of training, during this phase, the goal was to keep moving, but without being strict on structure, and with limited intensity.

In general, my take is that there is no need to be overly reactive, and even when we have a couple of suppressions, I tend not to implement changes without talking to the athlete in question and asking how they feel and if they are experiencing any additional stressors or else. After discussing with her and learning about the contextual information shared above, it was clear that both objective and subjective data were pointing to a situation in which it was wise to make adjustments, find an alternative plan (to relieve part of the stress), and then get back on track as soon as the data would bounce back, which we were able to do in about a week.

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The second case study is quite similar, but the stressor is more chronic as we are talking about a work-related situation that will last a few weeks to get resolved. As such, the athlete had already reached out to me to provide the required context and ask for a deload week to allow for more capacity in the direction of what was the main stressor in that period (work, not training). This was not an unexpected stressor as the previous one, but it was a strong psychological stressor that needed to be managed. Needless to say, I am fortunate to work with many athletes who really understand this concept well (care to join us?).

Here is the data:

Above we can see that we already went into chronic stress mode, so to speak, as the suppression is now lasting for about 2 weeks, and the baseline is stably below normal range. While the situation does not look good, we also know that this is a time-limited stressor, and will be resolved within about a week, hence we are likely to see a rebound at that point.

In the meantime, the approach is similar to what we are doing with the previous athlete, i.e. we keep moving, but with less structure and less overal volume, reducing intensity, and making sure we don’t burnout.

Talking about burnout

When stress becomes chronic and coping fails, the risk of burnout emerges. Burnout is characterized by emotional exhaustion, cynicism, and a sense of inefficacy.

Physiologically, it can be associated with long-lasting parasympathetic withdrawal and sympathetic dominance, and in practice with persistently low HRV (or the other way around!). In athletes, this picture overlaps with what is often described as overtraining syndrome. The consequences are not only a decline in performance but also significant risks for mental health and long-term well-being.

Monitoring HRV over time can allow us to spot these early warning signs, giving us the opportunity to intervene before exhaustion.

I’ve talked a few times in the past (including in this recent podcast) about how developing HRV4Training and working on HRV all these years for me personally has been mostly informative in the context of psychological stress and work stress, more than training stress. As a recreational athlete, training is hardly ever the problem in my day. Work, on the other hand, has been something I had to learn to manage, and in this context, the data has been extremely useful to show me that what I was doing and how I was living was unsustainable and detrimental to my health. Fast forward a few years, and I think I am getting there.

Rural Italy, because mental health. See you in Brisighella.

What can you do?

The value of HRV in this space is not in producing a number or a recovery score, but in opening a window into how the body is responding to the challenges of life and training. It is a reminder that stress is not inherently bad; it is part of adaptation. What matters is balance, and the capacity to return to baseline, or in other words, stability. HRV helps us see where we are in that balance, and, when interpreted in context, it can guide us toward healthier ways of coping, training, and living.

Beyond reflection, HRV can be integrated into active strategies. Cognitive reappraisal, in which we deliberately reframe stress as challenge, is linked to more adaptive HRV patterns. Practices such as paced breathing, HRV biofeedback, and relaxation techniques can also support recovery.

What HRV offers is a feedback loop. We measure, we reflect, we adjust, and we can see the impact of those adjustments on our physiology.

I hope this was informative, and thank you for reading!

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Marco holds a PhD cum laude in applied machine learning, a M.Sc. cum laude in computer science engineering, and a M.Sc. cum laude in human movement sciences and high-performance coaching. He is a certified ultrarunning coach.

Marco has published more than 50 papers and patents at the intersection between physiology, health, technology, and human performance.

He is co-founder of HRV4Training, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.

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