Some researchers believe that significant increases in resting heart rate (RHR) are a sign that you’re over-stressed, though the physiological mechanism behind the increase is not well understood. While , some believe it can be helpful.
“The key to using any heart rate measure is you must make comparisons to yourself,” says , a performance physiologist who’s conducted multiple . That means the commonly followed 10 percent rule—where you cut back training when your RHR goes 10 percent above your average—may be flawed. Here’s why, and how Plews suggests you collect your data:
“Look at your resting heart rate during a normal training week—one that’s not really, really hard or really, really easy,” Plews says. Take your RHR every morning that week as you lie in bed after waking, just as you’ve been doing.
You may see that your RHR changes day to day. The percent difference between your lowest and highest RHRs that week shows your personal variation in RHR. It may be more or less than 10 percent. For argument’s sake, let’s say you find your personal variation is 12 percent.
Next, take an average of your RHRs taken during that normal training week. You’ll compare RHR data from future weeks to this baseline average.
Going forward, take your RHR three or more days per week, then average them. If that week’s RHR average is more than 12 percent higher than your baseline RHR, that may be a sign you’re becoming overtrained and should rest or do low-intensity training. If it’s less than 12 percent higher, you’re likely ready for high intensity training.
While some researchers have found morning RHR is a useful tool for determining day-to-day workouts in sedentary people, Plews is not convinced it works well in the well-trained population. “Most training cycles are over a week, so it makes sense to average readings over a week to get a better reading of what you’re trying to assess,” Plews says.
However, he adds, “heart rate will never be the silver bullet of all measures” of training readiness. Some days, you may have a high heart rate, which could be interpreted as a sign that you shouldn’t be working out. But you may feel absolutely fine and get in a great training session.
The bottom line: Heart rate is just one of several measures you should use to determine how you should be training. “You might also use your motivation to train, how sore you’re feeling, and how tired you are,” Plews says.