Aerobic exercise is as important as strength exercises, as it combats lifestyle diseases like type 2 dibetics, cardiovascular diseases, high blood pressure. Choose any activity like running, cycling ,swimming or brisk walk, key is up your hear rate to cardio zone. One way to measure cardio fitness is VO2 max which the maximum oxygen your body utilizes during intense exercise.
I regularly go for runs, attends running events. If you have Fitbit device, you check your VO2 max, mine is 49. What do you do for cardio fitness and what is your VO2 max?