Running requires a great deal of energy, which is why it's optimal for challenging your cardiovascular and respiratory systems, as well as burning calories. It also puts stress on your body, which is evident in your the rise of your heart rate as you run. The less efficient you are at running, the more stress you incur and the higher your heart rate rises.
The most effective way to reduce the stress of running and, thus, lower your heart rate is to become more efficient at running. You might think this means going harder more often, so your body becomes stronger — but this is the wrong approach. You need to build your aerobic base, so your body efficiently delivers oxygen to working muscles with each beat of your heart. It'll then have to beat less rapidly to get your body what it needs to complete your run.
Why You Need Aerobic Efficiency
One of the most effective ways to build aerobic efficiency is to run slowly at a low heart rate for long-distance runs. When you run at a high heart rate, pushing your energy levels, you tend to burn stored carbohydrates. At a slower pace, you train your body to use fat for fuel.
Read More: Aerobic and Anaerobic Heart Rate Zones
A slow, aerobic run offers several other benefits — the endurance fibers in your muscles, the slow-twitch fibers, improve in function and blood volume increases, meaning your muscle cells get more oxygen. Your nervous system also relaxes and steals less energy from your running legs. All of this puts less stress on your heart, so it doesn't have to work as hard to pump blood as you run.
Improving Aerobic Efficiency
Running at an easy pace for the majority of your runs can give you these benefits. If you run four times per week, make three of them easy runs and, if you like, do speed work or hill work on the fourth day to build leg turnover and strength.
An easy pace means just that — easy. It's a pace at which you can easily talk or sing. The run is consistently performed at that level, without any intervals in which you spike your heart rate periodically.
Running at this pace is a challenge. You might love having permission to go slow — until you start to actually look at your times. A slow pace may not match your personal expectations and goals.
Know, however, that in the long-term, you're building a bigger, stronger engine to fuel your runs. As a result, your heart will have to work less hard at higher speeds, so you'll experience a lower heart rate and better performance when it counts. It may take you weeks or months to reap the results.
Read More: Is a Heart Rate of 170 Too High for Running?