Do squats count as cardio?

by Eric Trexler, Ph.D.

Study Reviewed: Cardiorespiratory and Aerobic Demands of Squat Exercise. Hong et al. (2024)

Key Points

Cardiorespiratory and aerobic demands were measured as 22 participants completed five sets of 10 repetitions of back squats at 65% of 1RM, with 3-minute rest intervals between sets.
The lifters reached oxygen consumption (VO₂) levels in the mid-to-high 40s, which very comfortably clears the bar for “vigorous” physical activity. Stronger lifters were able to reach higher relative aerobic work levels in comparison to weaker lifters.
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 – especially when you start digging into a detailed assessment of cardiac and metabolic training adaptations.

In the powerlifting world, it’s often joked that “cardio” refers to anything over five reps. Like most jokes, there is a grain of truth (or at least a grain of plausibility) beneath the surface. If you’d like to experience that grain of plausibility firsthand, go do a few sets of 20-rep-squats. As you’re contemplating the consequences of your decision halfway through the third set, it’ll be hard not to notice your heavy breathing and rapid heart rate. If you didn’t know any better, you might say it feels a lot like doing short-distance sprint work. Nonetheless, we can’t assume that the two physiological responses are similar (or will induce similar training adaptations) based on the subjective experience alone. To understand the aerobic and cardiovascular demand of a given type of exercise, you’ll want to examine specific cardiorespiratory parameters such as heart rate, oxygen consumption, carbon dioxide production, and minute ventilation. The presently reviewed study (1) did just that, examining cardiorespiratory responses to five sets of 10 repetitions of back squats at 65% of 1RM with 3-minute rest intervals between sets. Let’s dig into this study to see if the powerlifters were right about “cardio” all along.

The purposes of the presently reviewed study were: “1) to determine the magnitude of the cardiorespiratory response during squat exercise, including rest intervals relative to maximal aerobic capacity, and 2) to examine whether the cardiorespiratory response to squat exercise varies between individuals with higher and lower relative strength.” The study involved 22 healthy young adult males, aged 20-39, with over one year of resistance training experience and a relative squat one-repetition maximum (1RM) greater than 120% of their body weight. To roughly assess the impact of training status, the researchers split the group into “high strength” (relative squat 1RM above group median) and “low strength” (relative squat 1RM below group median) subgroups.

Participants completed three visits to the laboratory, with at least 48 hours between each visit. The purpose of the first visit was to obtain anthropometric measurements (height, weight, body fat percentage, and skeletal muscle mass) using bioelectrical impedance analysis, and to measure each participant’s maximal oxygen consumption (VO_2max) via a graded exercise test on a treadmill. The purpose of the second visit was to test the back squat 1RM for each participant. The third laboratory visit involved the actual experimental protocol in which participants completed five sets of 10 repetitions of back squats at 65% of their 1RM, with 3-minute rest intervals between sets. Throughout the entire protocol (during sets and during rest periods), oxygen consumption and heart rate were measured continuously. Rating of perceived exertion (RPE) was recorded after each set. Cardiorespiratory responses, including oxygen consumption (VO₂), respiratory exchange ratio (RER), carbon dioxide production (VCO₂), minute ventilation, and heart rate, were analyzed during both exercise and rest intervals.

Findings

Cardiorespiratory responses increased progressively across the five sets of squats. Heart rate peaked in the 5th set at 175 ± 9 bpm, corresponding to 89.7% of maximal heart rate. Similarly, VO₂ reached its highest point in the 5th set at 47.8 ± 8.9 ml/kg/min, which was 99.4% of the predetermined VO_2max. The average VO₂ across all five sets was 43.7 ± 3.3 ml/kg/min, equating to 92.2% of VO_2max. Participants’ perceived exertion (on a 10-point scale) ultimately reached a maximal level by the end of the squat session, increasing from 7 ± 1 in the first set to 10 ± 1 in the fifth set. During exercise intervals, VO₂ exceeded VCO₂, while VCO₂ surpassed VO₂ during rest intervals. RER fluctuated dramatically between exercise and rest periods, indicating shifts in substrate utilization and CO₂ buffering. Minute ventilation increased progressively across sets, from 61.3 ± 14.0 L/min in the first set to 85.7 ± 12.9 L/min in the fifth set during exercise intervals. Study results are summarized in Table 2.

The high strength group demonstrated higher body weight (90.7 ± 10.4 kg vs. 77.4 ± 3.1 kg, p = 0.004), greater skeletal muscle mass (41.8 ± 3.5 kg vs. 35.3 ± 3.1 kg, p < 0.001), superior squat 1RM (168.4 ± 16.4 kg vs. 114.4 ± 13.4 kg, p < 0.001), and higher squat 1RM to body weight ratio (186.5 ± 15.0% vs. 148.2 ± 11.6%, p < 0.001). The high strength group exhibited higher oxygen consumption relative to their VO_2max. Their peak VO₂ reached 108.0% of VO_2max compared to 93.7% in the low strength group. The average VO₂ (expressed relative to VO_2max) was also significantly higher in the high strength group (98.3 ± 8.0% vs. 86.1 ± 5.9%, p = 0.026). Despite differences in oxygen consumption, other indicators of exercise intensity were similar between groups. No significant differences were found in heart rate responses between groups across the five sets, and peak relative heart rates were comparable (91.0% vs. 90.0% of maximal heart rate, p = 0.245).

The internet chatter surrounding the presently reviewed paper seems to revolve around a single question: does squatting count as cardio? However, I think you need to answer a very important question before you even enter that debate: what do you mean by cardio? From my perspective, the idea that an exercise bout can “count as cardio” hinges on three primary criteria: 1) does it increase oxygen consumption to the level we’d expect from a cardio session, 2) does it induce the metabolic training adaptations we’d expect from traditional cardio training, or 3) does it cause the structural adaptations we’d expect from traditional cardio training? To reach an objective verdict, we’ll address all three.

Does lifting increase oxygen consumption to the level we’d expect from a cardio session?

The presently reviewed study found that lifters reached VO₂ levels in the mid-to-high 40s. Of course, this isn’t the first resistance training study to assess oxygen consumption, so it’s informative to cross-reference these values with the pre-existing literature. A great example of this literature is a paper by Vezina et al (2) which documents oxygen consumption during push-ups, curl-ups (also known as sit-ups), lunges, and pull-ups. Vezina and colleagues found considerably lower oxygen consumption (in the twenties rather than the forties; Table 3), but this difference is likely related to the characteristics of the exercise bout. Vezina et al (2) studied bodyweight exercises completed in three rounds of circuit training whereas the presently reviewed study (1) used heavier loads and an exercise that recruits a greater total mass of muscle tissue.

Interpretation

Whether you’re doing reasonably heavy squats or bodyweight circuit training , these studies pretty conclusively indicate that lifting “counts” as cardio if your definition of “cardio” is purely about burning calories. The VO₂ values reported by Vezina and colleagues correspond to MET values generally around 6 or above. “METs” are “metabolic equivalents,” which are simply multiples of resting energy expenditure. As such, doing an activity at 6 METs means you’re burning 6x the energy you typically burn at rest. We typically classify an activity as “moderate intensity” if the MET value is above 3 and as “vigorous intensity” if the MET value is above 6. In the presently reviewed study, the VO₂ levels in the mid-to-high 40s translate to MET levels above 11. For context, a MET level of 6 corresponds with running at around 4 mph and a MET level of 11 corresponds with running at around 7 mph (3).Notably, the exercise sessions we’ve discussed in this section are quite unlike the typical training of most MASS readers. Fortunately, a recent study (covered in MASS) measured oxygen consumption and energy expenditure in response to more traditional resistance training workouts. João and colleagues (4) had participants complete three different training sessions that included eight exercises in each (chest press, pec deck, squat, pull-down, biceps curl, triceps extension, hamstrings curl, and machine crunch). The low-intensity session consisted of 2 sets of 15 reps of each exercise at 60% of 1RM, the moderate-intensity session involved 3 sets of 10 reps at 75% of 1RM, and the high-intensity session required 6 sets of 5 reps at 90% of 1RM. As shown in Figure 1, the low-intensity session burned about 300 kcal in 44 minutes and the high-intensity session burned about 600 kcal in 116 minutes.

A very rough heuristic is that you tend to burn about 100 kcal per mile you walk or run (5). With this in mind, we can conclude that these resistance training sessions led to similar total energy expenditure in comparison to “typical” cardio sessions, but in a fairly inefficient manner with regards to time and recovery. If you wanted to burn 300 kcals with the smallest possible burden for recovery, you’d walk it. If you wanted to burn 300 kcals in the shortest time possible, you’d do a more conventional form of cardio. Nonetheless, the literature suggests that a typical resistance training session will still require enough total energy production (and specifically aerobic energy production) to suggest that it “counts” as cardio, as long as the session is completed with adequate effort and volume.

Does lifting induce the metabolic training adaptations we’d expect from traditional cardio training?

When you do cardio, you challenge the physiological systems involved with delivering blood, oxygen, and substrates to exercising muscle, in addition to challenging your body’s capacity to oxidize substrates for ATP generation. In response to a well-designed cardio program, your body increases mitochondrial volume to “build the machinery” that oxidizes substrates during aerobic energy production. In line with this adaptation, you’ll observe increases in mitochondrial enzymes associated with fat and carbohydrate oxidation. Another critical adaptation is an increase in the capillary density of muscle, which facilitates more rapid delivery of oxygen and energy substrates to the working muscle. So, does lifting induce similar adaptations?

Kind of. As reviewed by Mang et al (6), there is evidence that resistance training can induce similar adaptations, with two major caveats. First, the magnitude of these adaptations tends to be smaller in response to resistance training in comparison to traditional cardio. Second, the magnitude of these adaptations will be highly dependent on the characteristics of the resistance training program. If you’re doing a high-intensity, low-volume program (similar to a typical powerlifting or weightlifting program), you’re unlikely to observe a meaningful magnitude of aerobic training adaptations. In contrast, you’re far more likely to observe some of these aerobic metabolic adaptations if you’re doing a fairly low-intensity, high-volume program. The example for this type of program presented by Mang et al involves sets of 20-35 repetitions using 30-50% of 1RM, resulting in time-under-tension of 60-105 seconds per set.

In summary, we shouldn’t view the adaptations to cardio training and resistance training as dichotomous in nature. Some people will gain muscle and strength in response to a cardio program (depending on their baseline training status), and some people will experience aerobic adaptations in response to a resistance training program (depending on their baseline fitness level). If a totally untrained person begins a resistance training program, they’ll likely experience some degree of aerobic metabolic adaptations , such as increased mitochondrial volume and mitochondrial enzyme content. The more “cardio-ish” their lifting program is (for example, light loads, high time-under-tension, high volume, and short rest periods), the more robust those adaptations will be. However, the same individual would likely experience larger and more robust aerobic adaptations in response to a more traditional cardio program. So, if we’re basing our decision on aerobic metabolic training adaptations, we can say that lifting “kind of” counts as cardio, especially as the program becomes less power-oriented and more endurance-oriented.

Does lifting cause the structural adaptations we’d expect from traditional cardio training?

If you’re wondering what cardio is “supposed” to do, look no further than the name – “cardio” obviously refers to “cardiovascular,” and the cardiac (heart) tissue adapts considerably in response to this type of exercise training. In a previous MASS article, I explained cardiac adaptations to exercise (7) by describing two examples: an avid runner and an avid powerlifter.

Aerobic exercise leads to an adaptive increase in blood volume. Cardiac output (and, by extension, the volume of blood ejected in each heartbeat) increases dramatically during endurance exercise. As a result, the left ventricle of the avid runner is constantly dealing with large preloads (that is, the stretching that occurs as the left ventricle expands when it’s filling up with blood prior to contraction) that challenge the capacity of the ventricular chamber (Figure 2). While blood pressure increases during endurance exercise, it’s a relatively modest increase compared to resistance training. So, there is very limited “afterload,” which refers to the pressure the heart must overcome in order to eject blood out of the left ventricle so it can pass through the aorta and reach peripheral tissues. As a result, the runner’s heart will adapt to training by significantly increasing the volume of the left ventricular chamber due to high preload volume, which is known as “eccentric hypertrophy” of the heart. In contrast, they won’t experience a ton of thickening of the ventricular wall due to modest afterload pressure. The wall will tend to thicken a little bit, but just to make sure that the larger ventricle can pump blood effectively. As a result, it’s a proportional thickening that represents an overall improvement of heart function, when combined with the greater capacity of the ventricle.

In contrast, cardiac output doesn’t increase nearly as much during heavy resistance training as a hard session of endurance exercise. During heavy lifting, the increase in cardiac output is largely accommodated by increases in heart rate (rather than huge preload volumes). However, blood pressure can get astronomically high for very brief periods (i.e., during the concentric phase of a heavy repetition) throughout a powerlifting workout. This leads to considerable afterload pressures that the left ventricle must overcome to eject blood into the aorta. So, the wall of cardiac muscle tissue surrounding the left ventricle will thicken to produce more forceful contractions, which is known as “concentric hypertrophy” of the heart. In contrast, the overall volume of the ventricular chamber won’t increase a ton, because it’s not handling huge preload volumes in the first place. So, the powerlifter’s heart grows in response to training, but the primary stimulus (and purpose) of the growth is to overcome afterload pressure rather than to deliver more blood for aerobic metabolism.If we were to compare a pure steady-state cardio program to a pure (drug-free) powerlifting program, we would expect categorically positive cardiac adaptations from the cardio program (large increases in ventricular chamber volume with proportional changes in myocardial thickness) and fairly neutral from the powerlifting program (small increases in ventricular chamber volume and small increases in myocardial thickness). However, as previously stated with regards to aerobic metabolic adaptations, we shouldn’t view cardiac adaptations to resistance exercise and cardio as dichotomous. Cardiac adaptations to exercise depend on the characteristics of the exercise bout, and the key factors are preload and afterload. If a resistance training bout is structured to produce a large, sustained increase in cardiac output with modest afterload pressures, you’d expect cardiac adaptations that look pretty similar to cardio training. In contrast, if a resistance training bout is structured to produce a minimal increase in cardiac output with substantial afterload pressures, you’d expect cardiac adaptations that look very dissimilar to cardio training. As I noted in a prior MASS article, I would expect cardiac adaptations to CrossFit or circuit-type training to be most favorable and most similar to endurance training adaptations, while bodybuilding-type adaptations are probably more modest (perhaps a very slight benefit), and powerlifting-type adaptations are probably closer to neutral (minimal benefit, but minimal cause for concern for an otherwise healthy individual). For most MASS readers on pretty typical bodybuilding or powerlifting programs, I wouldn’t expect cardiac adaptations that are anywhere close to being on par with a cardio program.

Application and Takeaways

Whether moderate-to-high rep lifting “counts” as cardio depends on the criteria by which you judge cardio. Lifting can produce oxygen consumption and energy expenditure levels on par with cardio (albeit less efficiently), induce some of the aerobic metabolic adaptations we associate with cardio (albeit to a smaller degree), and may even induce some neutral to slightly positive structural adaptations of the heart (to a substantially smaller degree than cardio). Most importantly, we shouldn’t view training adaptations dichotomously. Resistance training delivers some of the benefits and adaptations we generally associate with cardio, particularly in the context of a fairly low-intensity, high-volume program that ramps up cardiac output. Nonetheless, it’s a good idea for most lifters to add in some “cardio-like” physical activity, even just leisurely walking for general health.

References

Hong S, Oh M, Oh CG, Lee HD, Suh SH, Park H, et al. Cardiorespiratory and aerobic demands of squat exercise. Sci Rep. 2024 Aug 8;14(1):18383.
Vezina JW, Der Ananian CA, Campbell KD, Meckes N, Ainsworth BE. An examination of the differences between two methods of estimating energy expenditure in resistance training activities. J Strength Cond Res. 2014 Apr;28(4):1026–31.
Herrmann SD, Willis EA, Ainsworth BE, Barreira TV, Hastert M, Kracht CL, et al. 2024 Adult Compendium of Physical Activities: A third update of the energy costs of human activities. J Sport Health Sci. 2024 Jan;13(1):6–12.
João GA, Almeida GPL, Tavares LD, Kalva-Filho CA, Carvas Junior N, Pontes FL, et al. Acute Behavior of Oxygen Consumption, Lactate Concentrations, and Energy Expenditure During Resistance Training: Comparisons Among Three Intensities. Front Sports Act Living. 2021;3:797604.
Loftin M, Waddell DE, Robinson JH, Owens SG. Comparison of energy expenditure to walk or run a mile in adult normal weight and overweight men and women. J Strength Cond Res. 2010 Oct;24(10):2794–8.
Mang ZA, Ducharme JB, Mermier C, Kravitz L, de Castro Magalhaes F, Amorim F. Aerobic Adaptations to Resistance Training: The Role of Time under Tension. Int J Sports Med. 2022 Sep;43(10):829–39.
Saunders AM, Jones RL, Richards J. Cardiac structure and function in resistance-trained and untrained adults: A systematic review and meta-analysis. J Sports Sci. 2022 Oct;40(19):2191-2199.