Cardio is a tool. Like any tool, it works beautifully for the job it was designed to do and poorly for everything else. The problem is not cardio, the problem is that most people are either using it for the wrong job or avoiding it altogether.

What cardio actually does well:

Cardiorespiratory fitness is one of the strongest predictors of long-term health outcomes we have. It is not a vanity metric. It tracks with cardiovascular disease risk, metabolic health, and all-cause mortality, and the people who avoid it are usually the ones who need it most.

Aerobic training improves how efficiently your heart moves blood, how well your muscles use oxygen, and how quickly you recover between hard efforts. That means recovering faster between sets, between sessions, and across a training week. Done properly, it supports your strength work rather than competing with it.

It also does something harder to measure but easy to feel. Regular aerobic work improves sleep, mood, and daily energy, which is the part people notice first. Lastly, it contributes to energy balance. Movement burns energy, and more movement burns more of it. That is real, and it counts.

Where it falls short:

Cardio contributes to energy balance, but it is a much smaller lever than most people believe. Your body compensates for increased activity by quietly reducing everything else, so you fidget less, move less between sessions, and feel hungrier. The number on the machine is not the number that lands in your day.

More importantly, cardio does not build or preserve muscle. Strength training is what tells your body the tissue you have is worth keeping, particularly when you are eating less. Without that signal, weight loss takes a real bite out of lean mass, and you end up smaller but not stronger. Cardio also does little for bone density, connective tissue resilience, and the practical strength that keeps you independent as you age.

Using it correctly:

The version that works is unglamorous. Build a base of easy aerobic work, the kind of effort where you can hold a conversation, and let it accumulate across the week. Walking counts, far more than people give it credit for. Add a smaller amount of harder work, once or twice a week, where you push into genuinely uncomfortable territory for short intervals.

Place it thoughtfully around your lifting. Hard cardio right before a heavy session will compromise that session, and stacking both at maximum intensity in the same day compromises both. Separate them where you can, and treat the easy work as something you can layer in almost anywhere. Cardio does not need to be escalated every week to keep working. It needs to be consistent.

Strength training and cardio are not competitors, and choosing between them is a false choice invented by people selling one or the other. Strength training builds and protects the tissue that carries you through your life. Cardio builds the engine that powers it. Nutrition decides whether either one can do its job.