Words by: Matt Fitzgerald, Lead PEAR Sports Coach and Pacer.

The two most basic variables of training for running events such as a Lexus LaceUp Running Series half marathon, 10K, or 5K are volume andintensity. Volume is how much you run and intensity is how hard you run. The most common mistake that runners make in their training is spending too much time at the same intensity. Training by heart rate is the easiest and most effective way to avoid this mistake.

Research has shown that running fitness increases most quickly when runners do about 80 percent of their training at low intensity (between 60 and 76 percent of maximum heart rate) and the remaining 20 percent at moderate intensity (77-91 percent of maximum heart rate) and high intensity (92 to 100 percent of maximum heart rate). The average runner spends less than 50 percent of his or her training time at low intensity, almost another 50 percent at moderate intensity, and less than 10 percent at high intensity. In other words, the average runner is stuck in what is known as the “moderate-intensity rut.”

One of the reasons why so many runners get stuck in the moderate-intensity rut is that they don’t know the difference between low and moderate intensity. In particular, they often think they’re running at low intensity when in fact they’re running at moderate intensity.

A heart rate monitor can help you break out of the moderate-intensity rut and start varying your training intensity more effectively. The five-zone heart-rate system used by PEAR Mobile, for example, makes it easy to avoid training at the wrong intensity. In this system, zones 1 and 2 represent low intensity, zone 3 is moderate intensity, and zones 4 and 5 correspond to high intensity. These zones aren’t the same for all runners, but the first time you use the PEAR Mobile app you complete a 20-minute fitness assessment that calibrates the zones to your individual fitness level.

Many runners use pace instead of heart rate to monitor and control the intensity of their running. Unfortunately, though, it doesn’t always work so well, because pace is a performance metric, so when runners keep track of pace, it often makes them want to run faster. Heart rate does a better job of holding runners back when they need to be held back, which is about 80 percent of the time.

Breaking out of the moderate-intensity rut is really a two-step process. We’ve already addressed step two, which entails monitoring your heart rate while you run. But monitoring your heart rate while you run is only helpful if you have already taken care of step one, which is planning your training in a way that obeys the “80/20 Rule” of intensity. This planning step can be intimidating for some runners, but you can take it off your shoulders by following a plan designed by an expert coach, such as the 80/20 Running plans available in the PEAR Plan Store.

The great thing about using heart rate to train by the 80/20 Rule is that it’s gentler and more comfortable than the 50/50 training approach that most runners practice unconsciously. This is one case where the easier way is the better way!

** Matt Fitzgerald is an acclaimed author, world-class running and triathlon coach, and sports nutritionist. His mission is to inspire, educate, and help athletes and fitness enthusiasts achieve their goals.  His books include Racing Weight, Diet Cults, The New Rules of Marathon Nutrition, and many more. He will be the lead pacer at each location of the Lexus LaceUp Running Series presented by Equinox.