Heart Rate Variability - Why it’s a must metric for Midlife Athletes
RHR, MaxHR, Vo2, FTP, SPM, RPM, tempo, threshold…. all familiar terms and metrics that many of you probably use in your daily training regimes. Us, midlife athletes do love our data but I’m guessing there is one metric - HRV (heart rate variability) - that doesn’t feature at all in your fitness files.
What is HRV?
HRV is measuring the gap (in milliseconds) between heartbeats. This gap between our heartbeats is not fixed and varies all the time and so HRV also looks at the amount of variation in these gaps between heartbeats. These gaps and variations are particularly pronounced when you compare someone in a stressed ‘fight or flight’ mode vs someone who is very relaxed. We’ve all experienced this ‘fight or flight’ mode where our heartbeats are thunderous and almost metronomic. There is hardly any variation, just a steady and heavy pounding. HRV is therefore a surrogate marker of our autonomic nervous system.
The autonomic nervous system is a self regulating system that controls many of our bodily functions such as heart rate, blood pressure, breathing, digestion and emotional response. As the name suggests, it is automatic - we don’t have to consciously think about doing any of its functions.It operates by receiving information from the environment and from other parts of the body. It’s made up of 3 parts, but the two of particular relevance to athletes are the sympathetic and parasympathetic systems. The sympathetic and parasympathetic systems tend to have opposing actions in which one system will stimulate a response where the other will inhibit it. The sympathetic system is viewed as a quickly responding system that mobilizes the body for action where the parasympathetic system is believed to act much more slowly to dampen responses. If, for example, you are facing a threat and need to flee, the sympathetic system will quickly mobilize your body to take action. Once the threat has passed, the parasympathetic system will then start to dampen these responses, slowly returning your body to its normal, resting state.
There is an interrelationship between heart rate and HRV which is critical to understand. Typically as an athlete is exercising at an intense rate, heart rate will be high whereas HRV will be low because the body is in a sympathetic state. As the athlete ends exercise and the heart rate decreases, HRV will slowly start to rise because the parasympathetic system is increasing and dampening the sympathetic response. HRV is a useful metric for measuring increases (high HRV) and decreases (low HRV) in parasympathetic activity.
At this point if we’re going to start to learn to use HRV it’s probably useful to focus a little on the parasympathetic system. It’s largely concerned with the conservation and restoration of energy, by causing a reduction in heart rate and blood pressure and by facilitating the digestion and absorption of nutrients and discharge of waste. The Vagus nerve is one of the main components of the parasympathetic system which oversees a vast array of crucial bodily functions, including control of mood, immune response, digestion, and heart rate. It establishes one of the connections between the brain and the gastrointestinal tract and sends information about the state of the inner organs to the brain via afferent fibers. By stimulating the vagus nerve, you can send a message to your body that it's time to relax and de-stress, which leads to long-term improvements in mood, wellbeing and resilience. The activity of the vagus nerve is called vagal tone and like many things when we age, vagal tone declines with age. Resting heart rate is a good measurement of vagal tone, whereas HRV is a measurement of the response or modulation on heart rate. Interestingly one of the ways us midlife athletes can increase our vagal tone is regular aerobic exercise amongst other things (Journal of American Heart Association).
So why is higher HRV associated with parasympathetic activity? It’s because the parasympathetic system is faster to affect the heart and thus the gaps between beats are more varied as the change in heart rate is happening over a shorter period of time.
How can I measure HRV?
Previously the only real way to measure HRV was via an ECG. Technology advances and research has brought HRV measurement in reach of all of us using either our phones or wearables. For example I use the HRV4Training app which uses my iphone camera to measure changes in blood volume in my index finger. It takes a minute, which I do first thing every morning. For a more detailed guide to measuring HRV I’d recommend reading Marco Altini’s blog (Marco is the founder of HRV4Training).
Why should HRV be my most important metric?
Alan is a physiologist and health/fitness/performance coach for endurance athletes and encapsulates why and how HRV can be used to help inform our training. Very simply, if your HRV is low, indicating a decreased parasympathetic state, then take a rest day or do a very light, easy training session.
Part of the reason why we all exercise is to get the benefit of positive training adaptations in our body. However, if we train or do hard sessions when our body needs recovery this will likely lead to negative training adaptations beginning with fatigue, functional overreaching, (a short-term decrement in performance as a result of increased training stress) non-functional overreaching/overtraining. We can avoid this by measuring our HRV and monitoring it over a rolling 7 day period so we do the sessions (and that includes rest) when our body needs it. Conversely, we can use our rolling average HRV measurement to do those hard sessions which can drive positive training adaptations. Increasing trends in our HRV illustrate that we are coping well with the training load which should lead to performance gains. Studies have shown that monitoring HRV and actively adjusting training loads according to our HRV trends can result in some performance gains, particularly for us midlife athletes.
Adjustments don’t need to just be reactive. Many of us midlife athletes experience stress from external factors such as work, family etc in addition to the stress we apply via training. If we’re experiencing stress, and hence low HRV due to external factors we can positively influence matters by adjusting our training. We know there are a number of things we can do to boost our HRV. One of the best ways is by doing aerobic low intensity exercise. Stringing together a period of aerobic low intense sessions can help to drive up HRV which is not just a good thing generally in our lives but can allow you to start introducing more intense sessions.
Why is this more relevant to midlife athletes?
We know that HRV decreases with age and reaches a low point in middle age so us midlife athletes are already likely to have lower HRV simply due to our age. Then layer on top life’s stresses from work, family, illness etc and there are even more reasons why our HRV is likely to be low. It’s crucial therefore that we don’t push our HRV scores even lower by constantly doing hard training sessions. The dangers are that we drive ourselves into an overtraining spiral which can lead to injury and/or illness and very likely significant time of rest. It’s important then that we learn to strike a balance, doing low intensity aerobic exercise when our HRV is low and then only adding intensity when we see positive trends &/or higher HRV scores. Typically how this will play out in practice is that us midlife athletes will only be able to do 1 or perhaps 2 intense sessions per week. Anything more and we’ll see our HRV trend starting to head in the wrong direction. A good approach to keeping this all in balance is the polarised training advocated by the likes of Stephen Seilor which is very simply translated into the 80/20 rule - 80% of your sessions should be at low intensity and 20% at high intensity. You can listen to Stephen explain this approach in our previous podcast.
In this newsletter we mention HRV4Training for measuring heart rate variability, and they have kindly given us a
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