That's where basic fitness comes in. 10 minutes of high stress activity a day builds more muscle mass than 2 hours of low impact cardio. Or to put it another way typists don't build large muscle in there forearm but a bricklayer does because stress is far more important than duration when it comes to muscle growth.

That's not to say cardio is pointless, rather unless your trying to build stamina for some reason cardio takes a lot of time for little short term benefit.