I think mountain biking is a great workout and it also keeps you sharp and trains your body and mind in ways that road riding never will. I've seen so may cyclists who lack strength, coordination, skill and ability to ride up or down a simple curb or some other simple obstacle. They have to stop and walk their bike and these aren't really old guys, they're still younger men, what a shame...If you regularly mountain bike then riding over curbs or some other obstacles is easy.