During the summertime, the environment adds external heat, forcing your body to work harder to maintain a healthy core temperature. Evans compares running in the heat with other forms of resistance training. While the precise effect varies by runner and conditions, the point is, you can’t evaluate your summer pace as though the weather conditions were irrelevant. This means summer training quite literally can help you run faster in cooler races because it’ll feel easier to maintain that quicker clip. On an easy run, Evans recommends sticking to a 3 or 4 out of 10 RPE.