Analysis of physiological changes in response to acute stressors

Blog post by Marco Altini
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Inspired by the different analysis that our users started putting together to investigate the effect of various stressors (training, travel, alcohol intake, etc.) on their HR and HRV  we redesigned the Acute HRV Changes analysis Insight.

Instead of looking only at day to day variations following training (is your HRV reduced after more intense workouts?) we will let you pick different parameters and explore day to day (acute) variations not only with respect to training but also for alcohol intake, travel, sick days and menstrual cycle.
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This way you'll be able to analyze more systematically over periods of 3 months how your body is responding to these different stressors, instead of only looking at them anecdotally from the history page.

The new acute HRV changes analysis will be available in about a week.

What's an acute change anyways?

We talked about acute HRV changes a couple of times already. Acute stressors are events that affect your physiology in the immediate future. Think about an intense aerobic workout, an intercontinental flight, a night out with too many drinks, high caffeine intake, etc. Acute stressors are typically the easiest phenomena to interpret and reproduce, and looking at data in the context of acute stressors can help understanding how your physiology works. Looking at acute changes can also help in gaining confidence in the tools we use, as these changes should be captured more easily. Check out this post for some examples from our users, or this tweet, the latest example I could find. In the past we focused much on acute changes in response to training, which we also published in our first paper, however we wanted to provide you with a better way to explore your data and annotations, hence the redesign of this feature.
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It's important also to remember that physiology is complex, and while acute HRV changes are often repeatable and easy to understand, there might be other factors behind the relationships that we are seeing (or not seeing) in our data. 

How does it work?

In the new Acute HRV Changes analysis you will be able to look at acute changes in two different ways. For certain stressors, which have an impact on the following day physiology (e.g. alcohol intake or a workout), we will show you the difference in HRV between "today" (stressor day) and "tomorrow" (day after the stressor), averaged over three months of data. Did your HRV decrease after a certain event? By how much? Is this decrease consistent? That's what you will be able to see for training (rest vs training as well as different annotated intensities) and alcohol intake. On the other hand, some stressors last for several days (for example getting sick, menstruation and travel). For these stressors we will not look at day to day changes but at the average HR or HRV values in the two conditions. What's your normal HR? Does it change when sick? Hopefully, this is clear, otherwise you just need to wait a couple more days to play around with the update. See some additional screenshots below.

HRV4Training Coach

The same feature is available also in HRV4Training Coach, where you will also be able to select different time frames, and analyze acute stressors for periods ranging between 30 to 90 days. For teams and coaches, you'll be able to run this analysis on all your athletes, as shown below for a few examples.

We hope you'll enjoy the feature :)