Research indicates that poor aerobic fitness is associated with a high risk of heart disease as well as death from various causes. It's as dangerous as chronic illnesses and smoking. Yet cardiorespiratory fitness is the one risk factor not routinely checked at doctor visits - unless you request it.
Your doctor can measure cardiorespiratory fitness through what's called your maximal oxygen consumption (VO2 max) or from readings taken while you do an aerobic workout. This reveals your body's capacity for transporting and using oxygen during exercise. In between doctor visits, for a quick snapshot of your cardiorespiratory fitness profile, you can use an online calculator to test yourself. It's not the same as having an actual test, but you'll get a good idea of where you are for your age.
The good news about cardiorespiratory fitness is that you can improve it. How? By exercising on a regular and consistent basis. In healthy adults, high-intensity interval training (HIIT) more effectively raises cardiorespiratory fitness than moderate-intensity continuous training, even if you burn the same number of calories. Yes, you'll huff and puff more during the periods of high-intensity exertion, but they alternate with rest intervals. And an HIIT workout typically takes less time to complete than a traditional cardio workout.