Heart Rate Variability (HRV)
Heart rate variability (HRV) is a relatively new way to assess the effects of stress on your body, although it has been known and used since the 1980's. Heart rate Variability (HRV), also called 'Beat-to-Beat variation' in heart rate, is simply the difference between consecutive heartbeats. Heart rates can vary due to breathing cycles (even if someone does not breathe during the recording), but it should be kept in mind that HRV should be measured while you are relaxed and calm - NOT while you are breathing heavily! Heart rate variations occur because of varying electrical activities within cardiac pacemaker cells at different times of inhalation and exhalation. Heart activity is controlled by the parasympathetic nervous system which manages "rest and digest" functions, where relaxation plays a major role. Heart rate variability is increased by physical activity, deep breathing, and stretching/yoga/recovery-focused exercises. Heart rate also varies between individual people due to their autonomic nervous system (ANS) function, which controls your body's "automatic" functions such as heart beating, digestion or respiration. Heart rate variability can be measured in several different ways:
HRV can be measured through Heart Rate Monitor Watch straps over the chest. Heart rate monitor watches detect heartbeats with chest or wrist sensors, measure time intervals between them and determine HRV from the difference between consecutive heartbeats. Heartbeat intervals are recorded for every 5 minutes during an entire recording period of 20-30 minutes.
High-Frequency HRV, i.e., HF power is a well-recognized marker/index of cardiac vagal activity. Heart rate variability is calculated by time and frequency domain analyses of HRV. Heart Rate Variability (HRV) is a non-invasive procedure that measures the beat-to-beat variation in heart intervals and produces indices based on these variations. Heart rate variability provides an accurate assessment of the autonomic tone and reflects the influence of both the sympathetic and parasympathetic nervous systems on the cardiovascular system.
Light's Criteria for Heart Rate Variability calculation: Heart Rate = beats per minute Heart Interval Time = number of seconds between consecutive heartbeats for specific 5 minutes Heart Frequency Band Power Spectrum. Power Spectrum = power contained within each band vs. total Output/ Output peak – Lowest peak within 0 – 0.4 Hz band Heart Rate Variability = Heart rate variability is the percentage of decrease/increase in Heart Rate for specific 5 minutes Heart Rate Low Frequency (LF) = 0.04 – 0.15 Hz Heart Rate High Frequency (HF) = 0.15 – 0.4 Hz Heart Rate Ratio (LF/HF).
Using HRV to understand performance:
Heart rate variability (HRV) refers to the variation of time between heartbeats. Heart rate is a non-specific marker for cardiovascular fitness and is influenced by factors including age, activity level, stress levels and medication intake. Heart rate variability on the other hand is specifically related to the nervous system, particularly the parasympathetic system which regulates the body's 'rest and digest functions. Heart rate variability provides an indirect measure of how well the nervous system is functioning and is used for gauging stress levels, recovery status and readiness for training.
What are some measures of HRV?
There are several measures that can be taken based on time-domain (frequency) or the number of consecutive beats in a certain period, or based on the time between Heart Beats.
R-R Intervals - The heart rate is derived directly from Heart Rate Variability data and displays Heart Rate (beats per minute) over time with Heart Beat intervals plotted against Time. This graph will show the variation of Heart Beat intervals and can be used to detect Heart Rate patterns which may be useful for recovery or training.
Heart Rate Recovery (HRR) - Heart Rate Recovery is the reduction in Heart Rate occurring immediately following cessation of activity. Heart rate recovery can be used as a measure of recovery status and is typically based on Heart Beat Intervals immediately after exercise with Heart Beats plotted against Heart Rate. HRR can be used as a measure of recovery status and is typically based on Heart Beat Intervals immediately after exercise with Heart Beats plotted against Heart Rate.
HRV Number - The number derived from Heart Rate Variability data is usually displayed as a numerical value over time (e.g. the HRV number will be displayed as a number from 1-100 every minute).
What are some ways Heart Rate Variability can be used?
Heart Rate Variability can be used for three primary purposes:
To benchmark training status – Heart Rate Variability is used to gauge how well an athlete is recovering from their previous training session. Heart Rate Variability increases during training as Heart Rate increases and Heart Rate Variability decreases as the Heart Rate returns to a resting value. Heart Rate Variability is therefore used to determine training status; if Heart Rate Variability is high following a training session, then the training load can be reduced due to an elevated Heart Rate and fatigue levels. If Heart Rate Variability is low immediately after training, then Heart Rate Variability indicates low fatigue levels and Heart Rate can be increased for the next training session. Heart Rate Variability is therefore used to determine if an athlete is recovered or fatigued before training.
To gauge daily stress levels – Heart Rate Variability is used to assess Heart Rate variability between Heart Beats to gain insight into Heart Rate variability and Heart Beat patterns. Heart Rate Variability can be used to gain insight into Heart Rate variability and Heart Beat patterns which may indicate a heightened level of stress, particularly when Heart Beat intervals between measures are short or infrequent.
To assess readiness for training – Heart Rate Variability is often used as a marker for readiness for training or competition. Heart Rate Variability is typically higher when an athlete has just finished training or competition, and Heart Rate Variability decreases over time as the Heart Rate returns to a resting value. Heart Rate Variability is therefore used to gauge readiness for training; if Heart Rate variability immediately after training is high, then Heart rate variability can be utilised to gauge if Heart Rate variability and Heart Beat patterns indicate readiness for the next training session, as Heart Rate Variability decreases over time as Heart Rate returns to a resting value.
Conclusion
Hear Rate Variability is an effective tool that can support your fitness goals and readiness to train, compete and perform. It can provide an early indication of underperformance, stress or underperformance. HRV can be measured through readily available tools such as well-known HRM or other wearable devices such as Whoop etc. In context, HRV is worth trying to see if it supports your training.
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