%VO2max and VO2 Reserve (VO2R)
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Intensity expressed as a fraction of oxygen uptake — either of maximal uptake (%VO2max) or of the reserve between resting and maximal uptake (%VO2R), which closely matches %HRR.
Detail
Oxygen uptake (VO2) can anchor intensity in two ways:
- %VO2max — intensity as a percentage of maximal oxygen uptake (the ceiling of the aerobic system; see aerobic-system and vo2max-trainability).
- %VO2 reserve (VO2R) — intensity scaled to the span between resting VO2 (≈1 MET,
3.5 mL/kg/min) and VO2max:
Target VO2R = (VO2max − VO2rest) × %intensity + VO2rest
ACSM favors VO2R because it aligns almost one-to-one with heart-rate reserve (%HRR), since both subtract a resting baseline before scaling (see karvonen-hrr). In the ACSM classification, moderate intensity = 40–59% VO2R and vigorous = ≥60% VO2R — identical numbers to the %HRR bands (see intensity-classification). Note that %VO2max and %VO2R are not the same number for a given effort: because %VO2max does not subtract the resting baseline, a given %VO2max corresponds to a somewhat lower %VO2R.
VO2-based prescription is the most physiologically direct because it measures the actual metabolic rate, but it requires lab measurement (or estimation via METs, since 1 MET ≈ 3.5 mL/kg/min; see mets), which is why heart-rate proxies are used in the field.
Key facts
- %VO2max = fraction of maximal oxygen uptake; %VO2R = fraction of (VO2max − VO2rest), added to VO2rest.
- VO2R aligns ~1:1 with HRR (both subtract a resting baseline).
- ACSM: moderate 40–59% VO2R, vigorous ≥60% VO2R (same numbers as %HRR).
- %VO2max ≠ %VO2R for the same effort (no baseline subtraction in %VO2max).
- VO2rest ≈ 1 MET ≈ 3.5 mL O2/kg/min; lab-measured or MET-estimated.
Connections
- karvonen-hrr — %HRR, the heart-rate analog of %VO2R.
- intensity-classification — the moderate/vigorous VO2R bands.
- mets — METs as a practical proxy for VO2.
- vo2max-trainability — how the VO2max ceiling itself changes.
- aerobic-system — VO2max as the aerobic ceiling.
Educational content only — not medical advice. Always consult a qualified professional for individualized guidance, especially around injury, pregnancy, or medical conditions.