When most people think of heart rates, usually the more stable and consistent the better. While this is usually true for your resting heart rate, having a higher heart rate variability can actually better for your overall health. While having a stable resting heart rate is important, heart rate variability, or HRV, starts to come into play when you're doing more than just sitting around.
In order to fully understand the importance of HRV and how a wider range in HRV can be more helpful, it's important to understand just how the heart works, and how it adapts to internal and external conditions. There are essentially two portions of the nervous system that regulate your body functions depending on your current state and the internal and external factors applied to the body, the sympathetic and parasympathetic nervous system. The parasympathetic nervous system essentially controls the resting phase, putting more priority on digestion, muscle relaxation, and slowing of the heart rate. The sympathetic system is the 'fight or flight' system, kicking the body into high gear, cutting down on the digestion rate in the gastrointestinal tract, and jumping that heart rate up.
While most people look at these are binary states, one is on while the other is off, it's actually more of a sliding scale where the body could be anywhere in between the two. There are many subtle environmental changes that can cause a slight shift in one direction or another, for example, our body shifts more towards the sympathetic side when we see light. This makes sense as we are usually more active during the day, so the light stimulus triggers our body towards a more sympathetic state.
Even the act of breathing in and out shifts our system slightly back and forth. Inhaling causes a shift towards the sympathetic side to help distribute oxygen to the rest of the body more quickly while exhaling shifts more towards the parasympathetic to rebalance our system.
This is where HRV comes in. A higher range of HRV allows our body to shift and rebalance itself between higher ranges of heart rates. This is especially important in situations where the body is recovering, be it from exercise, illness, or even just stress. Recovery puts a higher strain on the body increasing the body's heart rate. A higher HRV can help keep things balanced throughout the recovery, preventing other possible complications due to hypertension if your body can't naturally get its heart rate back down to normal levels.
If you're looking to track your HRV, most fitness trackers will do the trick. It's best to do it first thing in the morning since so many things can affect it, or just take an average throughout the day.
