The ideal long run speed is between 55 to 75 percent of your 5K pace, with a 65 percent average pace. According to study, running faster than 75% of your 5k speed on a long run does not bring much additional physiological benefit. However, running slower than this range will cause you to use more energy leading to a less efficient workout. For example, if your normal 5K time is 17 minutes and 50 seconds, your long run pace should be somewhere around 8:30 to 9:00 minutes per mile. If you ran faster than this range you would be using more energy than necessary and if you slowed down below this range you would be forced to work harder than intended which could lead to injury. There are two ways to improve your long run performance: by running faster or by running longer. It's better to cover the same distance in fewer hours rather than more hours, because prolonged exposure to a stress such as a high heart rate or low temperature can lead to injury. Therefore, it is recommended that you try to maintain a constant pace throughout your long run. This way you can avoid any sudden changes in tempo that may cause unneeded discomfort. Pacing yourself also gives your body time to recuperate and prepare for the next race or training session.