Some researchers believe that significant increases in resting heart rate (RHR) are a sign that you鈥檙e over-stressed, though the physiological mechanism behind the increase is not well understood. While , some believe it can be helpful.
鈥淭he key to using any heart rate measure is you must make comparisons to yourself,鈥 says , a performance physiologist who鈥檚 conducted multiple . That means the commonly followed 10 percent rule鈥攚here you cut back training when your RHR goes 10 percent above your average鈥攎ay be flawed. Here鈥檚 why, and how Plews suggests you collect your data:
鈥淟ook at your resting heart rate during a normal training week鈥攐ne that鈥檚 not really, really hard or really, really easy,鈥 Plews says. Take your RHR every morning that week as you lie in bed after waking, just as you鈥檝e 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鈥檚 sake, let鈥檚 say you find your personal variation is 12 percent.
Next, take an average of your RHRs taken during that normal training week. You鈥檒l 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鈥檚 RHR average is more than 12 percent higher than your baseline RHR, that may be a sign you鈥檙e becoming overtrained and should rest or do low-intensity training. If it鈥檚 less than 12 percent higher, you鈥檙e 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. 鈥淢ost training cycles are over a week, so it makes sense to average readings over a week to get a better reading of what you鈥檙e trying to assess,鈥 Plews says.
However, he adds, 鈥渉eart rate will never be the silver bullet of all measures鈥 of training readiness. Some days, you may have a high heart rate, which could be interpreted as a sign that you shouldn鈥檛 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. 鈥淵ou might also use your motivation to train, how sore you鈥檙e feeling, and how tired you are,鈥 Plews says.