Once we have a cardio habit and our 30 minutes per day is easy-peasy, we can get fancy. There are lots of ways to do that.
One is to go faster. Maybe we’ve been walking and we can progress to jogging or running. Maybe we’ve been biking and we get to go farther in the same amount of time. If we’re on a treadmill, we set the pace higher.
Another way is to go harder. We bike uphill. We set the resistance on the elliptical trainer higher.
Alternatively, we can go longer. Sure, we can do half an hour, but maybe an hour is not so much of a snap. That 5K turns into a half marathon turns into a marathon…
My favorite way is to add intervals. Intervals are kind of like sprinkles of harder/faster in our regular workout. Once we’ve warmed up, we spend a minute going as hard and fast as possible to get our heart rate up toward the top of our cardio range. Then we spend a minute or two at an easier level to bring the heart rate down to the bottom end of our cardio range (but still at or above 65% of our maximum). A half-hour cardio workout might have five or six intervals in it (five minutes warm up, five minutes cool down, twenty minutes doing intervals). Those sprinkles actually improve our cardio fitness faster because our bodies learn to recover from the hard work faster. We burn more calories and boost our metabolism without spending all day at the gym.
It's also a good antidote to the boredom that can set in during long cardio sessions. Yay!