This 20-week 50 mile/100K Ultra Run training plan requires the use of a heart rate monitor. It was designed by Eric Orton, using his proven training principles developed from 21 years of coaching experience. It works well for seasoned runners and following this plan will prepare you for your 50 miler /100K by including all of the elements used by Eric in training his personal coached ultra runners. To start this plan you should have completed a 90 minute long run or more and have an experienced background in running, including marathons. The workouts included in most weeks alllow you to customize the plan to your capacity for weekly volume. Weekends are very specific, with a focus on "quality" back to back runs. The exception is in R&R weeks every fourth week when training is greatly reduced for 4-5 days. These R&R weeks will allow for adaptation and improved performance.