Well, in my limited experience of mountain biking, it is very different than road biking. You have brief periods of steep ascents (which are often anaerobic). But much of the time, you are soft pedalling because you are going slowly to keep from running into something and falling.

Road cycling really emphasizes sustained aerobic power. This might be why your husband is outdoing you. On mountain bikes, your technical riding skill and climbing ability is on par with his.