From an exercise physiology perspective, a 10-day cycle better prioritizes the recovery period, “which is where all of your adaptations take place,” says Mario Fraioli, a Bay Area-based coach who works with a number of Olympic Trials-level marathoners, internationally-ranked ultrarunners, and competitive age-group athletes. “A lot of runners stress about fitting two workouts and a long run in every week, but there’s no universal formula that says that has to be the case or is the best way to structure a training cycle,” says Fraioli. Hein experienced this firsthand and credits the extra days with helping her feel better during marathon training. “I felt like my body needed more recovery time between long runs,” she says, and the 10-day cycle helped her achieve that.