Heart Rate Variability (HRV) - by Emily Henderson

Heart Rate Variability (HRV) Training

I’m sure we’ve all had our fair share of good and bad days in the gym. Since starting CrossFit, I’ve certainly had weeks where the PRs just keep coming, and then suddenly a sub-maximal clean just won’t come off the floor. I would be willing to bet that the difference between these two extremes lies
in the state of the nervous system. CrossFit demands a lot from both your muscles and your nervous system, so just as we break a muscle down and allow it to recover, so too do we stress the nervous system so it can recover, adapt, and become stronger.

It’s pretty easy to tell how your muscles are recovering. But is there a way to make sure your daily habits are enabling your nervous system to recover? For the past few months or so, I’ve been measuring my heart rate variability (HRV) using a heart rate monitor and a small receiver that sends data to an app on my phone (well, whenever I remember in the mornings). Measuring HRV is by no means an exact science, so I am testing it out just based on curiosity.

HRV is a measurement of the time gap between your heartbeats as you inhale and exhale. Although your resting heart rate might be measured as 50 beats per minute, the heart doesn’t work like a clock that ticks at a steady, unchanging rate. There are actually small changes in the pace of each heartbeat due to the interplay of the sympathetic and parasympathetic nervous systems. When you exhale, the parasympathetic nervous system (which allows your body to “rest and digest”) sends a signal to your heart, which causes it to slow down. But when you inhale again, that signal goes away and the sympathetic nervous system (sends your body into “fight or flight” mode) speeds up the heart rate again. To function optimally, we need a balance of being able to get the heart rate elevated during a workout, and being able to slow the heart rate down when we try to sleep.

When measuring HRV, a higher variability is better because it reflects a more optimal balance between your SNS and PNS. HRV is currently being used to monitor fatigue in athletes, because overtraining often causes either the SNS or PNS to become too dominant. So say I notice a trend where my HRV keeps dropping. This could be a warning sign that I need to take another day off, or maybe I need to sleep and eat better.

If you’re interested in this type of feedback, I use the ithlete HRV monitor/app. But regardless of whether you track HRV or not, I just wanted to bring attention to how important it is that we take care of more than just our muscles-our brain is a powerful tool as well.

Emily