Women Work Harder Cardiovascularly Than Men During HIFT and Kettlebell Training
New research finds women experience significantly higher heart rate and ventilatory load than men during the same high-intensity functional workouts.
Summary
A study from California State University San Marcos compared how men and women respond to two popular high-intensity workout formats: high-intensity functional training (HIFT) and kettlebell complexes. Despite working at a similar percentage of their VO2max, women showed meaningfully higher heart rates, peak heart rates, ventilation, and respiratory exchange ratios than men. Blood lactate, perceived exertion, and mood ratings were similar between sexes. HIFT also produced higher metabolic demands than kettlebell complexes overall. The findings suggest that when men and women perform the same workout, women experience a greater cardiovascular stress relative to their capacity. This has practical implications for how trainers and clinicians should design and monitor high-intensity exercise programs, and for understanding cardiorespiratory fitness — a strong predictor of longevity — across sexes.
Detailed Summary
Cardiorespiratory fitness, measured by VO2max, is one of the strongest known predictors of all-cause mortality, making the science of how different populations respond to intense training directly relevant to longevity. This study adds important nuance by examining whether men and women experience the same physiological demands when they perform identical high-intensity exercise protocols.
Researchers at California State University San Marcos recruited 17 men and 18 women to complete two popular workout formats: high-intensity functional training (HIFT), which involves compound movements like squats, pulls, and pushes performed at speed, and kettlebell complexes (KC), which chain multiple kettlebell exercises in sequence. The team measured oxygen consumption, heart rate, ventilation, respiratory exchange ratio, blood lactate, perceived exertion (RPE), and a feeling-scale score throughout exercise.
The central finding was striking: women demonstrated significantly higher mean and peak heart rates, higher percentage of maximum heart rate, higher ventilation relative to maximum, and a higher respiratory exchange ratio than men — all pointing to greater cardiovascular and metabolic strain. Yet relative oxygen consumption (%VO2max) was statistically similar between sexes. Men had higher absolute VO2 in liters per minute, as expected given greater body mass. Blood lactate, RPE, and mood scores did not differ between groups, suggesting both sexes perceived the effort as similarly hard despite the objective cardiovascular gap.
Comparing the two exercise types, HIFT consistently elicited higher aerobic demand and ventilation than kettlebell complexes, reinforcing it as the more metabolically intense modality.
The practical implication is significant: women performing the same workout as men face a proportionally greater cardiovascular stimulus. For trainers, clinicians, and anyone programming high-intensity exercise for longevity or health, sex-specific intensity targets — not just matched workload — may be warranted. Monitoring heart rate rather than only perceived exertion could prevent under- or over-training in women.
Key Findings
- Women had mean heart rates 22 beats per minute higher than men despite similar relative VO2 during the same workouts.
- Women's peak heart rate averaged 183 vs. 167 bpm in men, indicating a greater cardiovascular ceiling response.
- Respiratory exchange ratio was significantly higher in women, suggesting greater carbohydrate utilization relative to fat.
- Blood lactate, perceived exertion, and mood scores were statistically equal between sexes despite objective cardiac differences.
- HIFT produced higher aerobic demand and ventilation than kettlebell complexes regardless of sex.
Methodology
This was a controlled exercise-physiology study with 35 participants (17 men, 18 women) who completed both HIFT and kettlebell complex protocols. Multiple cardiometabolic and perceptual variables were measured continuously or at intervals during exercise. The cross-over design allowed within-subject comparison of both training formats.
Study Limitations
The summary is based on the abstract only, as the full text is not open access; methodological details such as exercise order, rest intervals, and fitness level of participants are unavailable. The sample was relatively young (mean ages 22–27), so generalizability to middle-aged or older adults pursuing longevity-focused training is limited. The study did not control for menstrual cycle phase, which can influence cardiovascular and perceptual responses to exercise in women.
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