The two branches of the autonomic nervous system — the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS) — play key roles in maintaining physiologic equilibrium in our bodies. The SNS functions as an accelerator, in that it is responsible for the “fight or flight” response that occurs with stress, while the PNS functions like a brake, in that it slows physiologic activity, such as when we relax.
Heart rate variability refers to fluctuations in the time interval between heart beats. High-frequency heart rate variability (HF-HRV), fluctuations that occur at the high frequency range (and also known as respiratory sinus arrhythmia), is considered a good indicator of parasympathetic nervous system (PNS) activity. Simply put, HF-HRV is an indicator of how well one’s physiologic brakes are working. Higher heart rate variability is good, because this is indicative of better fitness and a healthier cardiovascular system. Higher HF-HRV is also associated with better sleep, more positive emotions, better mental health, and a decreased likelihood of having diabetes or hypertension.
Changes in heart rate variability in a given individual can be indicative of how stressed or fatigued an individual is. Elite athletes may monitor heart rate variability to avoid over-training, such that lower variability is indicative of the need for rest and recovery. Aside from physical fitness, monitoring heart rate variability can be one means to track the impact of stress on an individual. (Persons motivated to monitor heart rate variability can find various types of monitoring devices, including applications that use a smartphone’s camera.)
Interestingly, heart rate variability appears to have an interactive relationship with social behavior. Persons with higher HF-HRV have been found to have a greater degree of affiliation in groups, or a greater sense of belonging. And, persons who increase their social integration over time (i.e., interacting with more people) have been found to have increases in their HF-HRV. This pattern does not seem to be related to how extraverted individuals may be.
It is well-established that social integration and social support are good for health, both physical and mental. Persons who are socially isolated tend to have poorer health outcomes. The functioning of the parasympathetic nervous system, as reflected in heart rate variability, appears to be an important pathway for this link.
With respect to health behavior, higher HF-HRV is a specific benefit that comes from exercise. Additionally, it would appear that increasing one’s social integration also is beneficial for the cardiovascular system and overall health.by