These high-work and moderate-duration sessions typically last not more than 1 hour and 30 minutes, which is normally the amount of time that an endurance athlete has unfilled for working out on most days of the week. Interval workouts are theoretically the most potent, but they also present the greatest amount of stress on an athlete. Athletes should use a prearranged, methodical, and progressive overload with the aim of avoiding overtraining. Many veteran endurance coaches and athletes will tell you that being a tad undertrained on race day is better than being over-trained!