Want to get thoroughly exhausted in 16 miles @ 7mph avg? Ride a mountain bike on some tough trails. Today's ride included sections of tight, rocky, hilly singletrack and sections of smooth, flowing doubletrack. There were long climbs and blistering descents. Unlike my last MTB outing, there were no falls today. I was completely wiped out after the ride and spent most of the afternoon asleep in a recliner.