This training plan is designed as a 20 week progression culminating in a 100 mile trail run or similar length FKT attempt. Before beginning the plan you should, at a minimum, be running 4 hours a week for at least a month, or 3 hours of running with an additional 2-3 hours of cross training. The plan could also be applied to training for a mountainous 100k or 50 miler and easily adapted to a 50k by a reduction in the overall volume.