When you do a set of heavy squats, or hammer out two sets to failure on the bench, you might find yourself gasping for air. You look down at your smart watch, and see you’re in zone 3 territory.
So that naturally begs the question: is lifting weights cardio? Are you getting even more benefits from your strength training than you planned for?
It's a fair question. It might feel like you’re getting a legit cardio workout. However, heart rate and breathlessness aren't the full picture. The type of stress, how long it's sustained, and what's actually limiting your performance all determine whether you're building cardiovascular fitness or just feeling tired.
Let's break it down, and examine what the research says.
What is “Cardio” Anyway?
When exercise scientists talk about cardiovascular exercise, they're referring to sustained, rhythmic activity that keeps your heart rate elevated in a specific zone for an extended period.
Think running, cycling, swimming, rowing. The defining feature is continuous aerobic demand: your heart and lungs are working to deliver oxygen to working muscles, and that delivery system is the limiting factor.
Cardiorespiratory fitness, measured by VO2max, is one of the strongest predictors of longevity and overall health. To improve it, you need sustained time at moderate-to-vigorous intensities, typically 20-60 minutes per session, where your cardiovascular system is the bottleneck.
Strength training is a different kind of stress. Your muscles' ability to produce force is the limiting factor. When you reach failure on a set of bench press, it’s because your chest, shoulders, and triceps gave out. Not because you hit your cardiovascular capacity.
That distinction matters more than how hard you're breathing.
The Squat Study: Evidence to Support Lifting as Cardio
There is some science that suggests lifting weights may have cardiovascular benefits.
A 2024 study by Hong et al. in Scientific Reports measured oxygen consumption during back squats in 22 trained men. The protocol: 5 sets of 10 reps at 65% of their one-rep max, with 3-minute rest periods between sets.
The results showed the following:
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Oxygen consumption hit 47.8 ml/kg/min by the 5th set, roughly 100% of their predetermined VO2max
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The stronger lifters actually exceeded their VO2max, reaching 108% during working sets
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Average oxygen consumption across all sets was about 92% of VO2max
Those numbers rival what you'd see during a hard interval on the bike or a fast run. But there’s one critical detail to take into account: those peaks only lasted for the duration of each set, roughly 30-45 seconds. Between sets, oxygen demand dropped sharply during the 3-minute rest periods.
Total time spent near peak cardiovascular demand was about 90 seconds across the entire workout.
Compare that to a 30-minute zone 2 cardio session or a HIIT workout where you're sustaining elevated heart rates for minutes at a time. The total cardiovascular stimulus is completely different to a lift, where your heart rate spikes, then immediately drops once your set is over.
As Eric Trexler, PhD, wrote in his analysis for MASS Research Review: "It's generally defensible to conclude that lifting counts as more than nothing with regards to cardio, but rarely serves as a fully adequate replacement."
Why a High Heart Rate Doesn't Always Mean "Cardio"
Your heart rate can spike for lots of reasons that have nothing to do with aerobic fitness. Stress, caffeine, anxiety, a near-miss in traffic. The heart rate itself isn't what drives adaptation. It's the sustained demand on your cardiovascular system to deliver oxygen over time.
During a set of heavy deadlifts, your heart rate jumps because your muscles need fuel and your body is managing intra-abdominal pressure, bracing, and exertion. But the set ends in 30-60 seconds. Your heart rate drops during rest. Then it spikes again on the next set.
This intermittent pattern is fundamentally different from the sustained demand of a 30-minute run or cycling session. Aerobic adaptation, the kind that improves your VO2max, strengthens your heart muscle, and builds capillary density in your muscles, requires prolonged time under that sustained cardiovascular load.
It’s the same reason that, if you carry a heavy box up a flight of stairs and your heart is pounding at the top, you can’t call that a cardio workout. Lifting weights follows a similar pattern. Brief bursts of high demand, followed by recovery.
What Lifting Does for Your Heart
None of this means lifting is bad for cardiovascular health. It's actually very good for it, just through different mechanisms than traditional cardio.
Research consistently shows that regular strength training has the following cardiovascular benefits (American Heart Association Scientific Statement, 2023):
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Lowers resting blood pressure. Both systolic and diastolic, with effects comparable to some blood pressure medications in mild cases.
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Improves insulin sensitivity. Muscle tissue is the primary site of glucose disposal. More muscle means better blood sugar management.
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Improves cholesterol profiles. Resistance training can reduce LDL and triglycerides while increasing HDL.
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Reduces cardiovascular disease risk. A 2019 meta-analysis found that even modest amounts of resistance training (less than an hour per week) were associated with a 40-70% reduction in cardiovascular events.
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Builds and preserves muscle mass. This becomes increasingly critical for metabolic health, fall prevention, and functional independence as you age.
These are real, meaningful cardiovascular benefits. They come through metabolic and structural improvements: better blood flow, healthier arteries, more metabolically active tissue.
But lifting just doesn't build the aerobic engine the way sustained cardio does. And VO2max, the measure of that engine, is one of the single strongest predictors of how long you'll live.
Energy Systems: Aerobic vs Anaerobic
The most basic way to differentiate different forms of exercise, and what really counts as “cardio” (for fitness purposes), is the energy system used.
Aerobic
The aerobic system uses oxygen to convert fuel into energy. It's slower but sustainable, powering you through long-duration activities like running, cycling, and swimming. When you go for a 30-minute jog, your aerobic system is working.
Training this system is what strengthens your heart, increases capillary density in your muscles, and improves your body's ability to deliver and use oxygen.
When people say "cardio," they're really talking about aerobic exercise: sustained activity that challenges your oxygen delivery system over minutes, not seconds.
Anaerobic
The anaerobic system produces energy without oxygen. It's fast and powerful but burns out quickly, lasting roughly 10-90 seconds of high-intensity effort.
When you grind through a heavy set of squats or sprint to catch a bus, you're relying primarily on anaerobic pathways (the phosphocreatine system for very short bursts, and glycolysis for efforts up to about a minute).
Most lifting falls in the anaerobic zone. A set of 8 heavy reps takes maybe 20-30 seconds. Even a grueling set of 15 might last 45 seconds. Then you rest for 1-3 minutes, letting your anaerobic systems recharge.
The aerobic system contributes during recovery between sets, but it's never the primary engine during the actual work.
How Much Cardio Do You Actually Need?
The American Heart Association and most major health organizations recommend:
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150 minutes per week of moderate-intensity aerobic activity (brisk walking, easy cycling, swimming), or:
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75 minutes per week of vigorous-intensity aerobic activity (running, hard cycling, HIIT), or:
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A combination of both.
Also recommended is at least 2 days per week of moderate-to-high-intensity strength training.
Notice both are listed. The research indicates the combination of cardio and strength training produces better health outcomes than either alone.
They complement each other. Cardio builds the aerobic engine. Lifting builds the structural frame. You need both.
If you hate traditional cardio, the good news is that "cardio" doesn't have to mean a treadmill. Walking counts. Playing a sport counts. A bodyweight circuit with minimal rest counts. Anything that keeps your heart rate up in a sustained way for 20+ minutes is doing the job.
The Bottom Line: Does Lifting Weights Count as Cardio?
Lifting weights is one of the best things you can do for your health. It lowers blood pressure, improves metabolic markers, reduces cardiovascular disease risk, and builds the muscle mass that keeps you independent and resilient as you age.
It has cardiovascular benefits, but it’s not “cardio” (using the generally accepted definition of what cardio is).
The brief heart rate spikes between rest periods don't add up to the sustained cardiovascular demand your body needs to build a stronger aerobic engine.
You don't need that much actual cardio. A few brisk walks per week, a couple of bike rides, a pickup basketball game - whatever keeps your heart rate up for 20+ minutes in a sustained way. Pair that with your lifting and you're covering both bases, and doing all you really need to maintain a strong and healthy body, inside and out.