Cardio is good for us. We need both cardio and strength training for basic health, as well as our athletic goals. But what actually counts as cardio? Can you count walking? Lifting weights? Anything so long as youre in the right zone? Let me break it down.What is the definition of cardio?Trick question! Cardio is a nickname for a certain rough category of exercise, and it doesn't have a precise definition. Youll find different definitions of it depending on who you ask, and a lot of the research on the benefits of cardio just calls it exercise." The Physical Activity Guidelines for Americans describes aerobic activity, or cardio, as when:...the bodys large muscles move in a rhythmic manner for a sustained period of time. Brisk walking, running, bicycling, jumping rope, and swimming are all examples. Aerobic activity causes a persons heart to beat faster, and they will breathe harder than normal.That matches how most fitness professionals use the term. Note that the key components are:Uses large muscles (like the legs; you cant get cardio by twiddling your thumbs)Is rhythmic (as when you pedal a bicycle for hundreds of revolutions)Can be sustained (like a 20-minute bike ride, but unlike a set of 10 squats)This definition includes walking, running, cycling, swimming, and using machines like a rower, elliptical, or stair machine at the gym.Is there a certain heart rate or zone that counts as cardio?No, there isnt a strict dividing line between what counts as cardio and what doesnt. The guidelines I quote above treat moderate intensity cardio as the minimum to target, but thats not defined in terms of heart rate. I have a breakdown here of what moderate really means, but briefly: Anything at the effort level of a normal-paced walk (about 20 minutes per mile) is moderate.I know thats not the answer you were hoping to find, so heres another data point: the American Heart Association says that moderate exercise corresponds to 50-70% of your maximum heart rate. (Vigorous is 70-85%.)Most of us dont actually know our true max heart rate, and formulas like 220 minus your age arent accurate. So take that with a grain of salt. Its more helpful to consider how exercise feels: Moderate exercise will get you breathing heavier than at rest, maybe sweating a little bit, and with a noticeably higher heart rate than when youre sitting quietly. You dont have to be out of breath; moderate exercise is conversational, in the sense that you could, literally, engage in conversation while you do it.If you want to get health benefits from cardio, you may want to pay more attention to intensity. Moderate exercise is great, but vigorous exercise (where it feels hard, and you wont be able to speak in full sentences) is also excellent to have in the mix. The Norwegian 4x4 is an accessible cardio workout that features plenty of vigorous work.Does walking count as cardio?Yes, in the sense that it meets the minimum guidelines. It is moderate intensity exercise and it counts toward your minutes per week (no matter what your heart rate is while you do it).But if you have athletic goals, walking alone is probably not enough to achieve them. If walking feels easy, you probably want to increase the intensity to increase your cardio fitness. Jogging or rucking would be good next steps.Does lifting weights count as cardio?No, lifting weights does not count as cardio (with a few exceptions, which Ill discuss in a minute.) Remember, cardio has to be rhythmic and sustained. If you arent doing the same movement over and over for, say, 10 minutes, its not cardio. So three sets of 10 on the chest press machine is definitely not cardio.And no, I wont change my answer based on what your heart rate monitor says. Your heart rate only measures the intensity of cardio exercise if you are doing cardio exercise. Strength training is still strength training (not cardio) no matter what zone your heart rate is in.So what are those exceptions I mentioned? Exercising with weights can count as cardio if it meets the definition: rhythmic and sustained. Most people dont do this! But if youre training for a kettlebell half marathon, which is 30 minutes of continuous lifting with a light kettlebell (you arent allowed to put the kettlebell down until time is up), then yes, that is cardio.I would also categorize the kettlebell ladder workout as a form of cardio. I do so with reservationsits not continuous for the whole 30-ish minutes, but then again neither is a lot of interval training. Kettlebell swings are definitely rhythmic and involve large muscles, and the workout is designed to get your breathing and heartbeat going faster than usual for pretty much the whole time. Ill allow it.Does HIIT count as cardio? High-intensity interval training definitely taxes your cardiovascular system, but it's not necessarily the best workout when you're looking for a way to get some cardio in. If you're doing true HIIT, it's very intense, very short, and may have longish rest periods in between the hard intervals. You're working your anaerobic system, not just your aerobic capacity, so it has some of the same caveats as lifting weights. What's more, a lot of "HIIT" videos out there aren't really HIIT, and aren't even necessarily good cardio. As I've written before, "HIIT" seems to mean "a video with a timer in the corner," regardless of what kind of workout you get out of it. If you're looking for a good cardio workout, it's better to find something where you know you'll be working aerobicallywhich means being able to breathe rather than gaspthroughout the whole workout.What other exercises count as cardio?Ive given some examples already, but let me give you a longer list of things that are definitely cardio, if you do them in any sort of normal way (steady state or intervals, especially if the intervals use active rest like walking).Running, jogging, or run/walk intervals (indoor or outdoor)Cycling (indoor or outdoor)Rowing on a gym machinePaddling or rowing a small boatJumping ropeDancing (truly the most underrated form of at-home cardio)Stairmaster or stepmill machinesClimbing machines like the Jacobs Ladder or VersaclimberElliptical machinesSwimmingRoller skating or rollerbladingYard work or housework that has you moving continuously (like pushing a lawn mower or shoveling snow)I have a list of cardio options here that goes into more detail about many of the above, and heres a list of chores and recreational activities that can also count (although many are moderate level, like walking).Hopefully these examples help you choose some exercise to do. If you have specific athletic goals, though (like running a 5K or passing a fitness test for work) youll want to look into a training program that is geared toward those goals.