What is Heart Rate Variability (HRV)?
HRV is a way to assess your readiness to tolerate stress. HRV is not to be confused with heart rate. Heart rate is measured in beats per minute, while HRV assesses the intervals between those beats. These intervals can vary. For instance, variation between two beats could be 0.9 seconds or 1.3 seconds. This variation between beats allows us to evaluate the state of someone’s nervous system state and their readiness to tolerate stress.
Relationship between HRV and the nervous system
The autonomic nervous system is responsible for controlling non-conscious functions in the body like heart rate, digestion and respiration. Furthermore, the autonomic nervous system can be broken down into two systems: sympathetic and parasympathetic nervous systems. The sympathetic branch is termed the ‘fight or flight’ system while the parasympathetic branch is known as the ‘rest and digest’ system. HRV assesses the relative dominance of the parasympathetic branch to the sympathetic branch. If an individual is more stressed, their sympathetic branch is more dominant, and when someone is recovered, their parasympathetic system is more active.
Relationship between parasympathetic and sympathetic systems and HRV
Variability between heartbeats relates to the different autonomic branches. For example, the parasympathetic system is associated with lower heart rates while the sympathetic system is associated with elevated heart rates. As a result, lowering the heart rate will allow more room for variability between heart beats, while increased heart rate will decrease the variability between heartbeats. When there is more variation between heart rates it is a sign that an individual is more recovered (parasympathetic dominant). On the other hand, when there is little variation, it is an indicator that the individual is likely over stressed and not well recovered.
Understanding your HRV is an indicator of your current nervous system state, revealing your current fitness, recovery, and readiness status. Many variables can impact your HRV and it is important to look for trends rather than comparing your HRV to others. HRV scores will vary depending on the individual, however, and it is important to note when your HRV drops for a period of time. When there is a dip in HRV, it is an indicator your nervous system is stressed, when this happens recovery will be diminished, risk of sickness increases, and injury rates may increase. Additionally, take note on the lifestyle, environmental, and nutritional habits that increase your HRV!