Thirty minutes of cardio typically taps into carbohydrate stores only. That is unless you’re doing prints, plyos, or some other high intensity cardiovascular training. On average 45 minutes to one hour of cardiovascular training with in 65-75 percent of your target heart rate zone of steady state cardio will put your body in it’s fat burning zone. Choose your favorite machine, or take it out doors! The point is to get moving! Peace!