This is a plan built off the exercise schedule outlined in Billal et al 2004 using progressively longer intervals at threshold pace over a 6 week training period to increase time to exhaustion in established endurance athletes. This is completed entirely at or below threshold running pace and requires an accurate estimate of threshold pace or maximal lactate steady state pace. If you do not have a preferred running threshold pace protocol, you may email me and I can add one to your plan. This plan is listed for intermediate athletes but will likely show robust response with beginners as well as moderate response with advanced athletes. For questions or comments, please email me.