The climbs: no summit, just a thousand short grunts
Do not let the lack of a real mountain fool you. Uwharrie is persistently, relentlessly hilly, and the climbs come at you in short, steep, punchy bursts the whole way. You hit a stiff grunt right off the start near mile 1, gaining a few hundred feet on rough trail before your legs are even awake, and the standout is Dennis Mountain deep in the 20 (a pitch that touches around 15 percent grade and stacks 300-plus feet into well under a mile). It is the accumulation that gets you. None of the hills is scary on its own, but they never stop coming, so the move is to hike the steep ones efficiently and keep your effort honest instead of charging every bump.
On the 40 you do every one of these climbs twice, and the second pass on the way home is where the day is really decided. Run the first 20 like the trip back does not exist and you will pay a steep tax on every one of those same hills coming home.