VO2max — Direct (Laboratory) Measurement

Maximal oxygen uptake (VO2max) is the highest rate at which the body can take up, transport, and use oxygen during maximal exercise. It is the criterion measure of cardiorespiratory fitness, expressed as mL·kg⁻¹·min⁻¹ (relative to body mass) or L·min⁻¹ (absolute).

Protocol: an incremental graded exercise test (GXT) on a treadmill (e.g., Bruce protocol) or cycle ergometer, increasing intensity each stage until volitional exhaustion, while a metabolic cart measures expired O₂ and CO₂ (open-circuit spirometry).

Criteria that a true VO2max (vs. VO2peak) was reached (classically need ≥2):

• A plateau in VO2 despite increasing workload (rise <~150 mL·min⁻¹ or <2.1 mL·kg⁻¹·min⁻¹).
• Respiratory exchange ratio (RER) ≥ 1.10–1.15.
• HR within ~10 bpm of age-predicted max.
• Blood lactate ≥ ~8 mmol·L⁻¹ post-test.
• RPE near maximal.

If exhaustion occurs without a plateau, the value is termed VO2peak. Direct testing requires equipment, trained staff, and screening for contraindications; for most general-fitness settings, submaximal or field estimates are used instead.

• Units: mL·kg⁻¹·min⁻¹ (relative) or L·min⁻¹ (absolute).
• Measured via graded maximal test + metabolic cart (open-circuit spirometry).
• VO2max criteria (≥2): VO2 plateau, RER ≥1.10–1.15, HR ≈ age-max, lactate ≥~8 mmol/L, max RPE.
• Without a plateau → reported as VO2peak.
• Gold standard but resource-intensive; submaximal/field tests estimate it indirectly.