The Exercise Habit Most Women Swear By Might Not Be Doing What They Think
If you've been faithfully logging your 30 minutes of moderate exercise most days of the week, you're getting the recommended weekly about of cardio. But a new study1 suggests that for women in midlife, that standard benchmark may not be moving the needle on cardiovascular fitness as much as we've assumed. Here's what you need to know.
About the study
Cardiorespiratory fitness (CRF) is one of the strongest predictors of long-term health, yet most exercise guidelines are built around absolute intensity thresholds, fixed values that apply the same way to everyone (regardless of fitness level). So for this study, researchers were investigating which exercise intensity levels are most strongly linked with better CRF in middle-age women.
Researchers recruited 73 women between the ages of 50 and 65, including 38 recreational runners and 35 inactive controls, representing a wide range of fitness levels (CRF ranging from 20 to 60 ml/min/kg).
Physical activity was tracked via hip-worn accelerometers for seven days, and CRF was measured through maximal cycle ergometer testing.
From there, researchers analyzed exercise intensity in two ways:
- Absolute intensity: Traditional exercise categories based on METs (metabolic equivalents), where moderate activity is defined as 3–6 METs and vigorous activity is 6+ METs.
- Relative intensity: Exercise intensity personalized to each participant’s fitness level, measured as a percentage of their individual VO2 max.
That distinction matters because the same activity can feel very different depending on your baseline fitness. A brisk walk may barely elevate one person’s heart rate while feeling genuinely challenging for someone else.
Vigorous intensity (not moderate) was the only threshold that tracked with fitness
The active group had significantly higher cardiorespiratory fitness (CRF) than the inactive group. When researchers analyzed activity using absolute intensity thresholds (the standard MET-based system), associations with higher CRF began to emerge at around 4.5 METs—near the upper end of the moderate-intensity range—and became progressively stronger at higher intensities, peaking in the vigorous range (≥6 METs).
Notably, activity in the lower portion of the traditional moderate range (3–4.5 METs) was not significantly associated with CRF in this group.
Researchers also analyzed exercise using a relative intensity model, which measured effort as a percentage of each woman’s individual VO₂max rather than assigning the same intensity threshold to everyone. This approach explained 70% of the variation in CRF, compared with 53% for the absolute intensity model.
So, accounting for individual fitness level provided a stronger explanation of differences in cardiorespiratory fitness than fixed intensity cutoffs alone.
Why the MET system falls short for midlife women
This study highlights a limitation of using fixed intensity categories to evaluate exercise. Traditional MET thresholds assume the same activity represents the same physiological challenge for everyone. But that may not reflect reality—especially in midlife, when cardiorespiratory fitness can vary widely between individuals.
According to this study's findings, accounting for each woman’s individual fitness level explained more of the differences in cardiorespiratory fitness than standardized intensity cutoffs alone.
Why cardiorespiratory fitness matters so much in midlife
CRF reflects how efficiently your heart, lungs, and muscles work together during sustained effort, and it's most commonly measured as VO2 max.
For women in midlife, CRF takes on particular significance. Hormonal shifts during perimenopause and menopause are associated with increased cardiovascular risk, and maintaining or improving CRF is one of the most evidence-based ways to counteract that trend.
Higher VO2 max is also associated with better cognitive function, more energy, and greater resilience as you age.
RELATED READ: The 5 Best Creatine Supplements For Women
How to gauge effort & safely push your intensity higher
Two simple tools work well to gauge effort and intensity:
- The talk test: At moderate intensity, you can speak in full sentences but not sing. At vigorous intensity, you can only get out a few words at a time before needing to catch your breath. If you can carry on a full conversation without any effort, you're likely working below the threshold that drives meaningful CRF improvements.
- Rate of perceived exertion (RPE): On a scale of 1–10, moderate effort feels like a 5–6 (noticeable but sustainable). Vigorous effort is a 7–8 (challenging, breathing hard, but not all-out). Aiming for that 7–8 range, even briefly, is where cardiovascular adaptations tend to accelerate.
- Heart rate zones: If you use a heart rate monitor, vigorous intensity generally corresponds to 70–85% of your maximum heart rate, roughly ≥64% of your VO2max in relatively speaking. A rough estimate of max heart rate is 220 minus your age, though individual variation is significant.
A few practical ways to introduce more challenge without overhauling your routine:
- Add intervals to your walks: Alternate 1–2 minutes of fast walking or uphill effort with 2–3 minutes of recovery pace. This is one of the most accessible ways to introduce vigorous-intensity bursts.
- Try incline walking: Walking on a treadmill at an incline (or finding hilly terrain) significantly increases cardiovascular demand without requiring you to run.
- Incorporate resistance circuits: Moving through strength exercises with minimal rest keeps heart rate elevated and adds a cardiovascular component to your training.
- Use exercise snacks: In a 2026 meta-analysis2 of 11 clinical trials, researchers found that short structured bouts of exercise (5 minutes or less, performed at least twice daily) significantly improved CRF in physically inactive adults.
- Progress gradually: If vigorous activity is new to you, start with one or two short intervals per session and build from there.
The takeaway
This study doesn’t mean walking is useless or that everyone should jump into high-intensity workouts. Moderate movement still supports overall health, longevity, mood, and metabolic function.
But if your goal is specifically to improve cardiorespiratory fitness, this research suggests that periodically reaching a more challenging effort level (whether that’s hills, intervals, jogging, cycling, hiking, or another form of exercise that feels vigorous for you) may play a bigger role than simply accumulating more low-to-moderate movement.