Building a solid aerobic base of cycling fitness is the most important first step in any training program. This is the first movie in a series of 4 base builder workouts that will build endurance using Denver's vast urban bike path network. The Base movies are long, from 80 to 95 minutes each, in order to build endurance. What makes these movies different is that they are on relatively flat terrain, leading to lower intensity and avoiding the high intensity of the steep mountain roads. Riding long durations at low-to-moderate intensity trains the body to use fat for energy while developing a superior cardiovascular system that can handle more strenuous workouts in the months ahead. Seek Out Cycling recommends using all 4 base building movies several times during the winter in order to lay the foundation of endurance required for a high level of fitness when the snow melts and the days get longer.