Heart Rate Variability (HRV) and Wearable Technology

For those that like to track their health by using data and wearable technology, heart rate variability (HRV) has emerged as a new marker for resilience. HRV is the variation in the time interval between heartbeats. A low HRV has been associated with many pathologies, whereas a high HRV is associated with a healthy response to stress, and overall wellness. Let’s dig into the association:

The autonomic nervous system is an unconscious system that regulates bodily functions such as heart rate, digestion, respiratory rate and several others. It controls the fight or flight response, and is divided into the sympathetic and parasympathetic systems. When the body is in a sympathetic response state, it does all the things you would want to fight or flight. Heart rate increases, the gastrointestinal system is inhibited, the pupils dilate, muscle tone increases, adrenaline is secreted. The parasympathetic nervous system’s role is to turn off that response. The muscles relax, the eyes constrict, and gastrointestinal activity resumes. The parasympathetic nervous system is controlled primarily by the vagus nerve. 

Your body has a system called homeostasis, which is basically a balancing system. These systems are delicate, and many pathologies stem from an imbalance of some sort. Too much of thyroid hormone and you have Grave’s disease (hyperthyroidism), too little and you have Hashimoto’s disease (hypothyroidism). The body is striving for the goldilocks zone, and autonomic nervous system function is the same. 

An interesting example of this is breathing. When you breathe in, your heart rate increases to oxygenate the tissues, and when you exhale, the heart rate decreases. There is even a difference between the nostrils. The left nostril is associated with the right brain (the creative side), and the right nostril with the left brain (the logical side). The left nostril stimulates the parasympathetic system, and the right, the sympathetic (Upadhyay-Dhungel & Sohal, 2013). Breathing with both nostrils creates homeostasis. So you can biohack this, and if you have to give a presentation and you’re nervous, plug your right nostril with your thumb and take several left sided breaths. 

The vagus nerve stems from the brain and controls organs throughout the body. It calms organs after a fight or flight response, and the rate at which it can do this varies from person to person, and is a proxy for overall health. Vagal tone refers to the activity of the vagus nerve, and the body is always balancing between these two systems with vagal tone being dominant. Vagal tone can be measured indirectly through heart rate variability.

If we have constant stressors in life, whether it’s overtraining, poor diet, work related stress, or a poor night’s sleep, the balance of tone is interrupted. The ability to switch gears quickly, (moderated by the vagus nerve) is a sign of a resilient human. Regular exercise is thought to modify this ability to switch gears. It is important to note that these are associations, and if you have a low HRV, it does not necessarily mean you are in poor health, it’s more likely a snapshot of a system that is dealing with an imbalance of stress. 

There are several HRV monitors on the market now, but I’m a fan of Morpheus. It can quickly track your HRV and give you a “recovery score”. With this information, you can adjust your workout accordingly. Bad night sleep and a poor score? Maybe today is not the day to try to get a PR on your squats. Fully recovered, go at it. That’s the idea. Monitoring HRV over time can give you insight into the stressors that personally affect you and you may just find yourself modifying your behaviors to get the most out of your training. 

References:

Upadhyay-Dhungel, K., & Sohal, A. (2013). Physiology of nostril breathing exercises and its probable relation with nostril and cerebral dominance: A theoretical research on literature. Janaki Medical College Journal of Medical Science, 1(1), 38-47. doi:10.3126/jmcjms.v1i1.7885