Volume of oxygen consumed per unit time, measured by open-flow respirometry, as a primary index of aerobic metabolic rate at rest or during exercise.
Use VO₂ when the question is aerobic metabolic rate — basal, resting, or under graded exercise. Measure it by open-flow (push or pull) respirometry from the difference between incoming and outgoing oxygen fraction times gas flow. Do not read VO₂ alone as energy expenditure: the caloric value of oxygen depends on the fuel mix, so pair it with VCO₂. VO₂ is strongest when flow rate, calibration, body mass, and activity state are fixed and reported.
| Primary value | Oxygen consumed per unit time, from inflow–outflow O₂ difference × flow |
|---|---|
| Common units | ml O₂/min (whole animal); ml O₂/kg/min or per lean mass (normalized) |
| Compatible assays | Home-cage metabolic chamber, resting metabolic rate, graded treadmill exercise, VO₂max test |
| Required boundary | Gas flow rate set to animal size and O₂ sensor calibrated to standard gas and fresh air |
| Do not infer alone | Energy expenditure, substrate use, fitness, or fat-free mass without VCO₂ and body composition |
Set pull/push flow so the chamber turns over fast enough to resolve change without diluting the signal (commonly higher for rats than mice). Calibrate the O₂ analyzer against a standard gas and fresh air before each run, and record per-second values so resting plateaus and exercise transients are both resolved.
Higher VO₂ can reflect greater aerobic demand, but it also rises with activity, thermoregulation below thermoneutrality, feeding, stress, and body size. Normalize to body or lean mass and report the activity state before comparing groups.
Store animal ID, body mass, lean/fat mass if available, ambient temperature, gas flow rate, inflow and outflow O₂ fraction, sampling interval, activity state (rest vs run stage), VO₂ per minute, normalized VO₂, calibration record, and instrument or software version.
Endpoint pages should cite the method literature behind the scored value and keep high-specificity protocol claims qualified unless the source supports them.
Endpoint articles link to adjacent products, software workflows, and sibling endpoints where the connection is useful and already routable.
