Absolute and relative physical activity intensity thresholds across diverse fitness levels: a cross-sectional study in middle-aged women.
Level 4 - case-series / case-control
Cross-sectional observational study
PubMed 42519471 · doi:10.3389/fspor.2026.1829167
What was done
A cross-sectional study evaluated 73 middle-aged women aged 50–65 years (38 recreational runners, 35 inactive controls) with cardiorespiratory fitness (CRF) ranging from 20 to 60 mL/min/kg. CRF was assessed using maximal cycle ergometer testing. Habitual physical activity was recorded for seven days using hip-worn accelerometry via the 4 Hz frequency extended method. The authors compared associations of CRF with absolute intensity (3–6 METs moderate, ≥6 METs vigorous) versus relative intensity (46–64% VO₂max moderate, ≥64% VO₂max vigorous) using partial least squares regression and cumulative intensity thresholds.
What was found
The active group exhibited higher CRF (41.4 vs. 27.7 mL/min/kg, p < 0.001) and accumulated substantially more vigorous activity (20.6 vs. 0.8 min/day, p < 0.001). Positive associations with CRF emerged at approximately 4.5 METs for absolute intensity, peaking above 6 METs. For relative intensity, negative associations diminished progressively, reaching equilibrium near 64% VO₂max. The relative intensity model explained 70% of CRF variance compared to 53% for the absolute intensity model.
Why it matters
Standard absolute MET cutoffs may mischaracterize exercise stimulus across varying fitness levels in middle-aged women. Tailoring activity intensity targets relative to individual VO₂max accounts for more variance in cardiorespiratory fitness.
Limits
The cross-sectional design precludes causal inference. The sample size is modest (n = 73), limited to middle-aged women, and comprised of two polarized cohorts (recreational runners versus inactive controls), which may not generalize to broader or mixed populations.
Cited by
- supports Vigorous-intensity physical activity is defined as greater than 6 METs or 7 to 8 on a 10-point perceived exertion scale.