Originally Posted by achoo

If he's unable to maintain the proper cadence, his threshold power is likely overestimated, depending on how long his rides are. Dropping cadence to keep power up will not extend muscular endurance to the point needed to ride 100 miles.

Do the first 40 miles at 90 rpm, then drop off to 70 rpm because of fatigue, and by 80 miles you're gonna be dead.