Resting heart rate, or pulse — the number of times your heart beats per minute — is a standard medical vital sign. But what your doctor can’t measure from the office, or doesn’t, is the more obscure, but equally important heart rate variability (HRV).
Imagine the planets stretched from the sun to poor, beleaguered ‘maybe I’m a planet, maybe I’m not’ Pluto. Each planet is a heartbeat. But see how the space between them varies?
That’s heart rate variability.
Heart rate variability measures the space between each beat, and how much it varies from the other spaces. Does your heart go Thump. Space. Thump. Space? Or does it go Thump. Space. Space. Thump. Space. Thump. Space. Space. Space.
If some spaces are longer and others are shorter, you have high heart rate variability. If all the spaces are the same, without peaks and valleys, you have low heart rate variability.
Which is Better?
High heart rate variability is a sign of health. Low heart rate variability is associated with aging, decline, illness and mortality.
What’s our maximum heart rate during exercise?
Our heart rate varies in response to what’s going on around us. As the energy needs of our body increase our heart rate quickens. It beats faster to increase the volume of oxygenated blood it can push to our muscles.
At rest a healthy heart beats between 50 and 90 times a minute. During exercise or activity it might double.
To find your maximum heart rate, subtract your age from 220. You shouldn’t exceed that target. When you exercise, aim to stay within 60 to 85% of that maximum heart rate. (Ex. if you are 30 your maximum heart rate is 190. Stay in a target zone between 114 and 161 BPM. For a 60 year old, the maximum heart rate is 160, so your target range is lower, 96 to 136.) Some physicians and trainers recommend staying within 50 to 75%. These are just guidelines. Individual goals should reflect your general fitness and heart health.
Why Does It Matter?
HRV measures your heart’s resilience. Its ability to bounce back from effort. High HRV lets you respond with speed and efficiency when your body demands more blood, more oxygen, more performance. High heart rate variability is a sign of flexibility, strength and responsiveness.
As such it is a key indicator of heart health and general fitness.
Stress, Aging and HRV
Decreasing heart rate variability has been inked with decline and is a predictor of mortality. Research links low HRV to illness, sexual problems, and reduced independence (our ability to perform everyday tasks with ease and confidence).
HRV is closely linked to stress and aging.
Humans engage in a constant cycle of stress and recovery. Our bodies are designed to mobilize when stressed, triggering various processes to restore balance. We fluctuate between homeostasis (balance) and allostasis (all the tricks our bodies use to respond to stressors and recover equilibrium).
HRV is a marker for two kinds of allostasis: acute (temporary stress) and cumulative (allostatic load). HRV is sensitive to acute stress. Mental effort such as complex decisions or speaking in public lower HRV. As a marker of cumulative wear and tear, our HRV has also been shown to decline with the aging process.
Our resting heart rate stays constant as we age but our HRV declines. Regular exercise slows aging and raises our HRV.
The more varied our heart rate (the space between the beats) the healthier we are. High HRV renders us better able to maintain balance (homeostasis), overcome stress, and slow down the aging process (the cumulative wear and tear or allostatic load).
Can We Improve our HRV?
The good news is yes, heart rate variability can be regained. HRV is a function of cardio health. The heart is a muscle. Like any other muscle, it gets stronger with exercise. Anything you do to improve your heart health will also improve its HRV.
High Intensity Interval Training (HIIT) alternates microbursts of intense activity with moderate exercise. It’s especially beneficial for cardiovascular fitness, weight loss, and increasing HRV. This training lets your heart practice a cycle of maximum effort and recovery. It’s in this recovery that the heart strengthens and HRV increases.
Every week brings new research on the impact of HRV. Recent studies have shown just 10 weeks of HIIT improved insulin function. HIIT may protect sedentary women against diabetes.
A technical analysis of HRV includes measuring bands by frequencies, classified as very low frequency, high frequency and low frequency. Each of these frequencies plays a special role in the autonomic nervous system and vagal health. High frequency bands reflect vagal activity. The low/high frequency ratio implicates sympathetic activity.
The very low frequency band indicates the balances between the vagal and sympathetic systems. New research shows that, unlike the other 2 bands, the very low frequency of HRV does not bounce back quickly after mental stress task. This underscores the link between stress, cognitive function, and HRV.
This research confirms that the low frequency is the “slow recovery” component of HRV and the other bands are the “quick recovery” components. This may shed light on the potential role of HRV on cardiovascular disease prevention.
HRV impacts multiples aspects of physical and mental healthy. Patients with depression and hostility or depressive disorders have reduced heart rate variability and may be at higher risk for coronary heart disease. Reduced HRV is also linked to anxiety sexual problems and reduced capacity for independence and self care in older people.
Our Evolving Understanding
A new tennis ball bounces with vigor, almost quivering with potential energy. It bounces high. Bounces low. Thwangs off the racket.
Now think of an old spent tennis ball. Limp. Not much bounce.
A healthy heart is like a new tennis ball. It is strong and elastic.
HRV measures the elasticity of our hearts. It is a key measure of heart health, where high heart variability signifies vigor, and low HRV is a sign of diminishing health.
Tracking our heart rate and HRV lets us evaluate steps we take to improve health and fitness.
Fortunately, there is a direct correlation between exercise and heart health. All we need to do is get started.