Heart Rate Variability

Heart rate variability or HRV refers to changes in the duration of consecutive cardiac cycles or heartbeats. Heart rate variability (HRV) involves measuring the specific changes in time (or variability) between successive heart beats and using that data to determine the current physical state of the body. The time between beats is measured in milliseconds (ms) and is called an 'R-R interval' or 'inter-beat interval' (IBI). HRV provides deep insight into the body's systemic condition. It is a non-invasive biomarker that tracks stress tolerance, adaptability and resiliency.

HRV is a directly associated with our Autonomic Nervous System (ANS). ANS is divided into two branches - Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS). Autonomic nervous system as a whole controls the physiological rate variation of the heart. The Sympathetic Nervous System controls our body's 'fight or flight' reactions and increases heart rate during stress situations. The Parasympathetic Nervous System activates our body's rest phase and is associated with recovery. Thus measuring HRV helps us understand the synchronization between sympathetic and parasympathetic nervous system and how well our Autonomic nervous system, as a whole,is functioning.

If the heart beats with uniform intervals between each pulse, it indicates low heart rate variability and is not desirable. High heart rate variability is characterized by heart beats with intervals of varying length. A high HRV indicates efficient functioning of of the parasympathetic response, that promotes relaxation, digestion, sleep, and recovery. The parasympathetic system is known as the 'feed and breed' or 'rest and digest' system. A low HRV indicates malfunctioning of the sympathetic response, the fight or flight nervous system associated with stress, overtraining, and inflammation.

HRV and cardiac health

High HRV is an indication of healthy autonomic and cardiovascular response. Higher heart rate variability suggests a higher ability to adapt to stress and also effective recovery, and acts as a good shield from stress related disorders and diseases. Low HRV may indicate that the poor functioning of sympathetic and parasympathetic nervous systems and lack of coordination between two systems. It is is a marker for cardiovascular disorders such as coronary heart disease, hypertension, ventricular arrhythmia, and heart failure. Autonomic imbalance results in morbidity and mortality from various conditions and diseases, including cardiovascular disease. Thus monitoring the autonomic nervous system through HRV is extremely helpful in monitoring our health status, particularly cardiovascular health.

HRV in fitness and sports

HRV measurement is increasingly being used by athletes and fitness enthusiasts in guiding their training workouts. Measuring HRV helps in preventing overtraining and exertion. Most often excess training and workouts lead to illness and injury and hence athletes need to understand and be able to measure the breaking point at which they need to stop and allow the body to rest and regenerate before springing back into action. Thus HRV is a good indicator of whether your central nervous system is in a fight or flight mode or at rest and repair mode and helps in accurately deciding on optimal training loads.

Measuring HRV

Earlier HRV monitoring was taking place in a controlled environment, such as a lab. However, with advanced technology, measuring the HRV has become pretty simple now. All we need to have is a smart phone, a heart rate strap and a small ECG receiver to plug into the headphone jack. There are many HRV apps available, download any app of your choice, and you are set to measure your HRV in no time.There is no set range for HRV because it is unique to each individual. One needs to create a baseline by observing data over a period of time. After few weeks you can notice certain patterns and ranges emerge, and these become standard parameters. Normally measurement is taken at resting phase and the ideal time for measurement is just after waking. Once the score is arrived, colored indicators flash on the screen. Most often, apps come with green, orange and red colored indicators indicating the readiness, mild stress and severe stress respectively.