Long runs are a staple of successful marathon training. They’re the anchor of your aerobic development, and one of the quality workouts you should complete every week of your training plan . After a long run, it’s normal to feel some soreness, stiffness, and maybe an urge to take a quick power nap to regain energy. But feeling drained for days, struggling to complete basic tasks, or consistently lacking motivation can signal something is off. A number of factors can lead to excessive fatigue after long runs, but one tends to stand out above the rest. Ahead, you’ll discover the common misstep among runners, and how fixing the issue can transform your training and level up your aerobic base. Running too fast is “the number-one reason” you feel totally exhausted after long runs, Matt Campbell, a certified personal trainer and run coach at PRO Club and Bay Club in Washington state, previously told Runner’s World. Your speed should never be what challenges you during a long run.…