In a nutshell, while they have much in common, the obvious differences correspond to different skills/abilities which don't all translate perfectly. For mounta

In a nutshell, while they have much in common, the obvious differences correspond to different skills/abilities which don't all translate perfectly. For mountain and trail racing, you have rough terrain rather than smooth roads; large elevation changes and high altitude rather than flat sea-level races; a generally longer duration; and a much slower average pace. You can think of road marathons as like Formula 1 car racing while mountain running is more like a race while towing a 2-ton trailer on a rough dirt road. Both events require power and speed, but the kinds of vehicles are quite different. An SUV can produce lots of torque but it would redline far before getting up to 200 miles per hour.