Women’s Heart Rates Ran Higher in a New Kettlebell vs Functional Fitness Study
UPLIFT IRON CLUBA New Study Put Kettlebell Complexes Against Functional Circuits
Two workouts can leave you equally sweaty and still demand different things from your heart, lungs and muscles. That is the useful question behind a new exercise-physiology study published on October 3, 2026 in the European Journal of Applied Physiology. Researchers compared high-intensity functional training, or HIFT, with kettlebell complexes, while also examining whether men and women responded differently during the sessions. The result is more interesting than a simple claim that one style burns more calories.
The researchers tested 35 young adults: 17 men and 18 women. Each participant completed both workout formats while investigators measured oxygen uptake, heart rate, ventilation, respiratory exchange ratio, blood lactate, perceived exertion and how pleasant or unpleasant the exercise felt. That combination matters. Heart rate alone tells you how frequently the pump is beating, not exactly how much oxygen the entire body is using, how much force the muscles produce or how hard the workout feels.
HIFT is an umbrella term for sessions that mix whole-body resistance exercises and conditioning movements, often in timed circuits. A kettlebell complex links several bell exercises into a continuous sequence, commonly without putting the weight down until a round finishes. Both can be challenging. Neither is automatically a superior hypertrophy program, and neither is synonymous with maximal strength training.
The investigators reported that the functional-training format imposed higher relative oxygen demand overall than the kettlebell complex format. They also found a notable difference between groups in cardiovascular measures. Those are acute responses measured during workouts, not evidence that one group will build more muscle, lose more fat or become fitter after months of training. The distinction is easy to lose when an exercise headline is reduced to a heart-rate number.
For a lifter choosing between a circuit and a bell, the practical question is therefore not which method wins an imaginary universal contest. It is which stress you actually want today: conditioning, repeatable technical practice, muscular endurance or progressive loading. The best workout is the one that produces the intended stimulus without turning every training day into a survival test.
Women’s Heart Rates Ran Higher—But That Is Not the Whole Story
The headline-grabbing finding was a higher average heart rate among women in the study. Across the measured exercise sessions, women averaged 156 beats per minute compared with 134 in men. Their average relative heart rate was also higher: 84% versus 76% of maximum. Peak heart rates were 183 versus 167 beats per minute. Those are group averages from a small experiment, not instructions for every woman to train harder or for every man to chase a particular number.
The investigators also measured relative oxygen uptake, expressed as a percentage of each person's maximum oxygen consumption. On that measure, the groups were much closer: approximately 62% of VO2max in women versus 59% in men, a difference that was not statistically significant in this sample. Men had higher absolute oxygen uptake in liters per minute. Those findings illustrate why one cardiovascular marker cannot stand in for the whole physiological picture.
Respiratory exchange ratio, which compares carbon dioxide production with oxygen consumption, was higher on average in women: 1.11 versus 1.05. Ventilation relative to maximum was higher as well. Yet blood lactate, perceived exertion and the Feeling Scale did not show significant between-sex differences. A workout can therefore register differently on a heart-rate monitor while the people performing it describe comparable effort.
There are several plausible contributors to different heart-rate responses, including fitness level, body size, cardiovascular characteristics, movement efficiency and the actual load each person handled. The women in this study were younger on average than the men, another reason to resist simplistic conclusions. The abstract does not establish which factor explains the entire gap, and the available summary does not justify saying that biological sex alone caused every observed difference.
For coaches, the sensible takeaway is individual calibration. A trained woman and a novice man do not become equivalent just because they follow the same timer. Record the load, the quality of movement, breathing recovery and perceived effort alongside heart rate. If a session is supposed to develop conditioning, use repeatable performance and recovery as evidence. If it is supposed to build strength, watch the reps and the load. The watch is useful; it is not the head coach.
Functional Circuits Demanded More Oxygen Than Kettlebell Complexes
When the researchers compared workout formats, HIFT generated a higher average relative oxygen uptake than kettlebell complexes: roughly 63% versus 58% of VO2max. Peak oxygen uptake reached about 81% versus 73% of peak capacity. Relative ventilation and respiratory exchange ratio were higher during HIFT as well. In plain gym language, the functional circuit asked more of the aerobic system during these specific protocols.
That does not mean a kettlebell workout is easy. A complex can combine cleans, front squats, presses and swings, keeping a large amount of muscle working while grip and trunk stability become limiting factors. But the exercise order, load and rest structure shape what the session actually tests. A bell heavy enough to make a clean technically demanding may force a slower pace than a bodyweight circuit built around frequent transitions and repeated large-muscle movement.
Earlier research by some of the same investigators compared post-exercise oxygen consumption after kettlebell complexes and high-intensity functional training. That 2024 experiment examined the so-called afterburn period for 60 minutes after exercise. It provides a useful reminder that acute oxygen demand during the workout and elevated oxygen use after it are separate outcomes. Neither is a reliable shortcut for predicting months of fat loss without knowing training adherence and overall energy balance.
There is also a training-goal distinction. Someone preparing for a hybrid race may want to tolerate repeated high-output efforts under fatigue. A recreational lifter may instead want an efficient conditioning supplement that does not wreck tomorrow's squat session. A kettlebell complex can serve that second role very well because its movements are easy to standardize once the athlete has learned them. A HIFT circuit can provide a broader mix of locomotion, calisthenics and machine work.
One limitation deserves emphasis: the published abstract does not provide every movement, load, work-to-rest interval and order detail. Without those details, it would be wrong to declare that HIFT always beats kettlebells for cardio. Change the bell weight, choose more demanding movements or shorten rest, and the response can change. The defensible conclusion is narrower and more useful: in this tested comparison, HIFT imposed a larger relative aerobic challenge.
Why Heart Rate and 'How Hard It Feels' Can Disagree
One of the most practical details in the new study is what did not differ significantly: ratings of perceived exertion. The women recorded higher average heart rates, yet reported effort was not significantly different from the men's. The same was true of measured blood lactate and the Feeling Scale. That makes a familiar gym argument less straightforward. A higher heart-rate reading does not automatically mean someone is trying harder, nor does matching perceived effort guarantee identical physiological responses.
Previous research has produced similarly complicated results. A 2019 study of bodyweight high-intensity circuit training found sex-related differences in relative oxygen consumption and some perceived-effort measures, but not the same pattern of relative heart rate across its testing points. A separate exercise-intensity study published in 2020 found that heart rate and percentage of maximum heart rate differed between men and women at certain cycling workloads even when some other markers, including perceived exertion, were comparable. Different protocols can produce different patterns.
Perceived effort remains valuable because it captures something a wrist sensor cannot: whether your legs are burning, your grip is failing, your breathing is manageable or the next repetition looks unsafe. A simple zero-to-ten scale is enough for many recreational workouts. Around six or seven out of ten can be a controlled hard effort; eight or nine is demanding and should be used deliberately rather than every time the timer starts.
Heart-rate data adds a second view, especially when measured consistently with a reliable device. Look at how quickly the pulse rises, how it recovers between rounds and whether a familiar workload is becoming easier over several weeks. Do not compare raw beats per minute with a training partner as if age, medication, fitness and physiology were identical. For very short kettlebell intervals, wrist optical sensors may also lag rapid changes, so the reading can be less informative than the performance in front of you.
A useful log has four columns: exercise and load; rounds or repetitions completed; perceived effort; and, optionally, heart rate or recovery. That modest amount of context makes it easier to spot real progress. The point of collecting numbers is to make better training decisions, not to award a gold medal to the highest pulse.
Build a 25-Minute Session Without Sacrificing Technique
For most lifters, the easiest way to use the research is to separate the goal from the exercise aesthetic. Here is a practical 25-minute session that keeps the useful parts of functional training while avoiding the usual mistake of making every movement a race. It is an illustrative coaching template, not the exact protocol used in the 2026 study.
Minutes 0–5: prepare. Do two easy rounds of five hip hinges, five bodyweight squats, five controlled push-ups against a bench if needed, and 20 seconds of relaxed marching or easy rowing. Practice the kettlebell clean with a light load before adding speed. A good warm-up should leave you ready to move, not already searching for the nearest floor.
Minutes 5–17: controlled kettlebell complex. Complete four rounds of six deadlifts, six goblet squats, five rows per side and four strict presses per side, resting 60–90 seconds between rounds. Select a bell that permits clean technique on the final press, the movement most likely to cap your load. If transitions are unfamiliar, put the bell down between exercises. There is no training prize for protecting the phrase 'unbroken complex' while the spine and shoulders negotiate a ceasefire.
Minutes 17–23: optional functional-conditioning block. Alternate 40 seconds of moderate rowing, cycling or brisk step-ups with 20 seconds of easy movement for six minutes. Aim for a hard-but-repeatable pace, not an all-out first interval followed by five increasingly tragic ones. The machine option makes pace easier to track; step-ups work when equipment is limited.
Minutes 23–25: recover and record. Walk slowly, note your completed rounds and rate the overall effort from zero to ten. If you are new to intervals, begin with two or three rounds and skip the final block. If your main program already includes hard lower-body lifting, keep the conditioning day separated from the most demanding strength session when possible.
Progress by changing one variable at a time: slightly more total reps at the same quality, a small increase in load, a shorter but still adequate rest, or more controlled rounds. Do not increase all of them together. A kettlebell complex becomes effective when it is repeatable enough to improve, not when the coach invents a new punishment every Tuesday.
What the Study Cannot Tell Us About Fat Loss, Muscle or Sex
A single laboratory comparison of 35 people is useful evidence about what happened during those exercise sessions. It is not a verdict on which sex is fitter, which workout makes the best body or which training style should replace strength work. The sample was small and relatively young, and the reported results concern immediate physiological responses. Long-term outcomes such as muscle size, maximal strength, race performance, injury risk and body composition were not established by this experiment.
There is a second reason to be careful: intensity is not the same as effectiveness. Higher oxygen uptake during a circuit may be desirable when aerobic demand is the target. It can also be irrelevant or counterproductive when the session is supposed to develop a heavy squat, precise overhead technique or high-quality hypertrophy volume. More breathing is not automatically more adaptation. Likewise, a kettlebell complex that produces a lower average oxygen demand may be exactly what a lifter needs for supplemental conditioning without excessive fatigue.
Longer-term comparative research offers a useful reality check. A 2026 randomized trial comparing high-intensity multimodal sessions with a schedule separating aerobic and resistance training found improvements in strength and aerobic fitness in both groups over seven weeks. The study did not establish one magical training arrangement for every goal. It supports the less glamorous idea that consistent, appropriately dosed work matters more than the branding on the class timetable.
For men and women alike, start with an individual baseline. Choose a movement you can perform safely, set a repeatable pace, and keep enough rest to preserve form. Track the actual work and your perceived effort. Use heart rate as supporting information, particularly if you have established your own normal training ranges. If a watch says the session was spectacular but the load, repetitions and technique are getting worse every week, believe the training log.
The best reading of the October 2026 study is not that women must train differently or that kettlebells lose to functional fitness. It is that two popular workout styles can impose meaningfully different cardiovascular demands, and that the same session can register differently across people. That is a reason for better individual programming—not another excuse to turn a group workout into a competition over whose heart beats fastest.
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