Downhill? 42 miles on a mountain bike is pretty tough. O_o
About 17 of it was downhill(ish) mountain biking isn't really downhill or uphill. Its switch-back up the hill through the gnarliest spots the trail-maker could find, jump down the hill then repeat. With a nice long uphill grind in between with a few streams, fallen trees and thigh sized roots thrown in for good measure.
One of the greatest sports ever.