Is Low Intensity Cardio Necessary?

At StrengthSpace, our clients often get deeply out of breath from the intense nature of our strength training. Even though we move slowly with simple exercises, the heart and lungs are still challenged. But despite this, not all clients get so winded. Perhaps an orthopedic condition like EDS or cardiovascular condition like POTS prevents them from pushing very hard during their strength workouts. And naturally, those clients want to know if additional low-intensity “cardio” is necessary. In this article, we’ll discuss the utility of different forms of “cardio,” from sprinting, to easier forms such as jogging, swimming, or brisk walking, and how they fits into our exercise framework.

Crucially, I am only talking about exercising for health in this article. If you are training for a marathon, then running is your “sport” and must be practiced regularly so your efficiency will improve.

What is “Cardio?”

In order to explain whether low-intensity “cardio” is necessary, we first have to define it. Now, I could be make this difficult by explaining that There is no such thing as cardio. By this, I mean that your heart and lungs don’t recognize where the demand for oxygen (or the surplus of carbon dioxide) is coming from. The cardiovascular system simply increases output to meet demand, regardless of whether you are leg-pressing or swimming.

High-Intensity Cardio – improving maximum output.

But let’s answer the question based on two common understandings of the word “cardio.” One way of understanding “cardiovascular training” is training that increases the maximal output of the cardiovascular system – namely the ability of our heart, lungs, and blood vessels to deliver oxygen to (and remove CO2 from) working muscles, which can be measured by VO2 max.

Training that does this can take any form, from weight lifting to swimming to climbing or wrestling. What is important is that it is high effort and involves reaching the limits of your endurance, such that you are too winded to continue. Whether this takes you 45 minutes or 45 seconds, you can still improve your capacity (measured by vo2 max) if you push yourself as hard as possible until you don’t have the wind to continue. This is what we do on CAR.O.L., and it’s amazing how small the amount of exercise can be if the intensity is high enough.

Low-Intensity Cardio – improving energy efficiency.

Another common use of the word “cardio” pertains to prolonged but deliberately sub-maximal activity. This is often what medical guidelines are referring to when they suggest a guideline such as: “do 45 minutes of “cardio” 3-5 days per week.”

With this type of training, the heart and lungs are working a little harder than at rest, but they aren’t the limiting factor. What you are really taxing is the ability of your cells to burn fat in their mitochondria (cellular energy factories). So long as you keep the intensity at a certain level, you can continue this type of activity for hours on end, even if it is more difficult that a leisurely stroll. And when you do this activity regularly, you get improvements within your muscles, as they get better at using fat for energy. Here’s a deeper dive on this low effort, or “zone 2” training, and why it is both useful but not as important as training maximal capacity.

The bottom line is this: low-intensity, or “steady state” cardiovascular training gives small, incremental improvements based on how much you do. The more the better. But the improvements are small, gradual, and take a long time to add up. The only way to “max out” these adaptations is to do hours of activity every day. We should all be engaging in lots of light activity to promote circulation, dispose of surplus blood glucose, maintain healthy joints, and improve our mental well-being. But we shouldn’t expect 30 minutes on a treadmill to ever be a transformative experience.

So what type of exercise should we prioritize?

A great analogy for life, and for exercise!

First, if you’ve never heard the rocks-pebbles-sand illustration for priorities, watch this short video. To summarize, I want you to imagine that you have to fit rocks, pebbles, and sand into a jar. The rocks are what is really important, the pebbles are useful, and the sand is good but of lowest importance. If you start with the rocks first, the pebbles and sand will easily fit in around them. But if you mistakenly start with the sand and pebbles, the rocks won’t fit.

Strength training workouts are the “rocks.”

For exercise, your strength training workouts are your rocks. No matter how healthy your heart and lungs are, you still can’t do anything if you lack the strength for the task, whether it is climbing a mounting, or standing from a chair. Muscle comes first, and defending our muscle mass MUST be our priority.

And luckily, for many clients, strength training does improve our maximal aerobic capacity. Due to it’s intense nature, it can leave us as winded as any interval training session, with all the attending benefits that short, high intensity conditioning can deliver.

Short, high-intensity cardio sessions are the “pebbles.”

After the essential rocks of strength training, we need to fit in the pebbles of intense cardiovascular training, be it hard “zone 4-5” training, intervals, or just anything that gets you severely out of breath. These workouts are important, but they can be done in just a few minutes! What matters is that we get deeply winded and empty our muscle glycogen. This will be improve our VO2 max, and improve our metabolic health and insulin sensitive, both of which are strong predictors of longevity.

Unlike strength training, if we neglect this for a while, we can regain our abilities here pretty quickly, which is why it is slightly less crucial than strength training. We can also measure the effects of this type of training through a continuous ramp-up endurance ride on CAR.O.L., which gives us a “maximum aerobic power” score that loosely estimates our VO2 max.

Is Low Intensity Cardio Necessary?
Low effort Cardio is the “sand.”

And finally, we have steady state “cardio,” which can look like jogging, hiking, swimming, playing sports, or vigorous gardening. Think of the “fat-burning zone,” of lighter activity that is sustainable for long periods. As we said, this type of activity is very health promoting, as it challenges the energy producing mitochondria in our cells to burn fat more efficiently.

Insulin resistance (the beginnings of metabolic dysfunction that leads to Type 2 Diabetes and heart disease) begins in the muscle, and keeping our muscles healthy is important. I think a nuanced argument can be had about whether or not strength training, sprinting, intervals, and higher effort cardio can’t offer similar benefits in less time, but that’s probably getting lost in the weeds. More activity is associated with better health outcomes (though burning calories to cause fat loss surprisingly isn’t one of them). Our bodies will regulate our appetites, have better circulation, and utilize fat for fuel better when we are more active.

Conclusion – Yes, low-intensity cardio is necessary, but get the high effort stuff in first!

For this reason, I would answer the original question in this way: Yes, “cardio” is necessary.

You most certainly should get very winded a few times per week to live a long healthy life. And you should also try to be physically active throughout the day.

But you should never let “5 hours of moderate intensity cardio per week,” or whatever other guideline you hear, prevent you from getting the rocks in the jar first. Higher effort strength training sessions are the most important “rocks” to fit into your week. Adding a few interval training “pebbles” will give you a significant additional benefit for improving your metabolic health and extending your life. After you have done these things, pour as much low intensity “sand” (light activity) into the “jar” as your schedule will permit, and do so with things you genuinely enjoy. If they don’t feel like a burden, you’re more likely to stick with them!