At this time, HR variability is primarily being used to examine physiological parameters in a few different ways:

• in chronic disease risk, cardiovascular disease risk, and health indications
• in looking at the impact of exercise training, especially in reference to functional and non-functional over-reaching, over training, and recovery.

HR variability is also considered an interesting marker for resilience and behavioral flexibility with applications for psychological and behavioral health.  “It is well established that low HRV is associated with a broad range of medical and psychological health problems.” (Wheat 2010) 

The goal is to maintain balance between the sympathetic and parasympathetic branches. “If we have persistent instigators such as stress, poor sleep, unhealthy diet, dysfunctional relationships, isolation or solitude, and lack of exercise, this balance may be disrupted, and your fight-or-flight response can shift into overdrive.”  HR variability can give insight into the ANS and be a valuable preventive tool metric.

A reduced HR variability (sympathetic) is associated with: 

• worsened anxiety and depression
• increased risk of cardiovascular disease and death
• myocardial infarction
• chronic heart failure
• unstable angina
• diabetes mellitus

An increased HR variability (parasympathetic) is associated with: 

• better cardiorespiratory fitness
• resilience to stress
• lower risk for many chronic diseases

A heart rate that is variable and responsive to demands is believed to bestow a survival advantage. The ability of the autonomic nervous system and sinoatrial node to respond dynamically to environmental changes results in increased HRV and generally indicates a healthy heart. A reduction in HRV is believed to indicate an inability or attenuation in the autonomic nervous system’s or sinoatrial node’s responsiveness to change. 

HR variability moves to a healthier level with:

• more mindfulness
• meditation
• sleep
• physical activity (Faye 2010)
• regular aerobic exercise which increases vagal tone (Singh 2019)

Monitoring the autonomic nervous system (ANS) with HRV has become a useful tool for cardiovascular health and fitness:

• providing insight to cardiovascular risk evaluation and diagnosis.
• using HRV to alert athletes of overtraining and to optimize training. (Singh 2019)

A resting ECG for a healthy individual will show obvious high frequency values. HRV can lower with aging, sedentary lifestyle, mental load, and possibly overtraining. (Singh 2019) Cardiorespiratory exercise training increases vagal tone therefore increasing HRV.

HRV is the beat-to-beat alteration of the R-R interval of your heart rate. The gold standard for measuring HR variability is to analyze a strip of an electrocardiogram (ECG) to determine the IBIs. With this method being impractical and unavailable to the general public, HRV can also be tracked with a HR/heartbeat monitor (finger/wrist device or a chest strap) and the purchase of an app to analyze the data. There are other ambulatory methods for measuring HRV, many of which are not practical to use at this time but may become more practical as technology advances.

Common metric measurement devices use the following technology: (Singh 2019)

1. ECG Devices: measurement of ECG still remains the most accurate way to measure HRV. Single lead ambulatory devices are available to analyze HRV.
2. Photoplethysmography (PPG): “an optical technique that detects blood volume changes in the microvascular bed of tissue under the skin’s surface.” (Singh 2019) This method can be affected by motion and skin characteristics. It measures lower frequency components (sympathetic) and changes in blood volume with each heartbeat. Interest in PPG for measuring HRV is rising due to accuracy and wear ability, but there has been limited validation of this method for tracking HRV. Ongoing research is in progress to improve the accuracy of this method.