So, is all stress created equal?
Your heart rate increases, your breath quickens and your muscles restrict in attention; but instead of being in the middle of a threshold session, you’re trying to manage the cumulative ebbs and flows of the day. When your Central Nervous System (CNS) detects a threat, whether it be physical or psychological, your adrenal glands release cortisol and the ‘fight-or-flight’ response is triggered. Unfortunately, the CNS cannot discern the difference between a stress event induced by a training stimulus or the stress accumulated from a day at work.
In order to improve in our running, we normally need to provide a stimulus and adequate time to recover. But what if our allotted recovery time includes an important meeting, children that won’t cooperate and a lack of sleep? In a study conducted in 2012 (Ruuska), 44 people were subjected to a two week training period including five sessions a week at an intensity of 75% of their maximum heart rate. Their mental stress was assessed prior to the training period. The research concluded that the subjects who reported low psychological resources and a lot of stressors in their life experienced a very low or in some cases no change in fitness over the course of the training period.
So how do we manage both?
Professor John Kiely proposed using Heart Rate Variability (HRV), being the time between heartbeats, as a useful indicator of stress levels. HRV decreases with stress placed on the body, including physical stress (e.g. workouts), chemical stress (e.g. poor nutrition) or emotional stress (e.g. strained relationships). Conversely, the higher a person’s average HRV, the less likely they are to be susceptible to stress from these sources.
The suggestion to use HRV as an indicator of stress arises because your HRV, despite it being a function of your heart rate, originates from your autonomic nervous system. Your autonomic nervous system has two components, parasympathetic and sympathetic. The parasympathetic branch, referred to as the ‘rest and digest’ system, decreases respiration and heart rate and increases digestion (among other things that we don’t consciously think to do such as salivate and produce tears). The sympathetic branch is our ‘fight or flight’ response and it reflects our response to stress and exercise, or seeing a snake out on the trail. HRV comes from these two branches competing simultaneously, the parasympathetic system telling your heart to beat slower and the sympathetic system telling your heart to beat faster.
As athletes, we are striving to have a high HRV. If our HRV is high, it means that our nervous system is responding to both the parasympathetic and sympathetic signals it is receiving and we are poised to deal with either the ‘fight or flight’ or the ‘rest and digest’ response.
If we have low HRV, it means either our sympathetic or parasympathetic system is inhibiting the other and consequently, our ability to respond to the inhibited system is reduced.
This is great and all, but how am I meant to track HRV?
According to Dr Marcelo Campos the gold standard of measuring HRV is through conducting an electrocardiogram (a whole bunch of wires connected to the chest and tests conducted in a medical environment). However, it is highly unlikely that you’ve got access to such technology so the next best thing is a chest heart rate strap. Dr Campos suggests checking your heart rate in the morning after you’ve woken up, a few times during the week, and track any changes you experience. A practical use of your HRV is to follow your own trend. If you’re taking steps to improve your fitness and reduce stress, over time you should see a gradual increase in your average HRV.
So, your HRV is low. What now?
Define the factors in your life that are generating stress and make them a priority for improvement. You may realise that work, your relationships and a lack of sleep are the driving forces of stress rather than your training. It is important to understand that stress is the difference between our experience and our expectations of those stressors. We can reduce the stress we experience by using techniques such as mindfulness, deep breathing and positive re-framing.
How do we manage stress practically as athletes?
During periods where life stress is unavoidable, reducing training intensity and training load is recommended in order to avoid the likelihood of injury, illness and mental fatigue. Securing your longevity in sport is important, because for most of us, we turn to endurance based activities as a way to mitigate daily stressors.
At the end of the day, our best indicator of stress and fatigue is self. As much as tracking HRV is a useful tool, if you’re feeling low or fatigued take that as a sign that rest may be the best form of training for that day and use the time to focus on recovery, good nutrition and other positive interventions centered around improving stress management.
Resources
Ruuska PS, Hautala AJ, Kiviniemi AM, Mäkikallio TH, Tulppo MP. Self-rated mental stress and exercise training response in healthy subjects. 2012.
Kiely J. Periodization Theory: Confronting an Inconvenient Truth. 2017.
Campos M. Heart rate variability: A new way to track wellbeing. 2019.