Glossary
Fitness words, plainly explained.
The terms you meet in VO2max articles, watch apps and training plans.
Absolute VO2max
Oxygen uptake in litres per minute, not divided by body weight. Matters on flat cycling and rowing.
Learn more →Cardiac output
Litres of blood the heart pumps per minute: heart rate × stroke volume. The main limit on VO2max.
Learn more →Cardiorespiratory fitness (CRF)
How well heart, lungs, blood and muscles supply and use oxygen. VO2max is its standard measure.
Learn more →CPET
Cardiopulmonary exercise test: a lab test with a mask analysing breath gases while exercise intensity rises to exhaustion.
Learn more →Fitness age
The age at which your VO2max would be typical. Lower than your real age is a good sign.
Learn more →Fractional utilisation
The share of your VO2max you can sustain in a race. Decides performance among people with similar VO2max.
Learn more →Haemoglobin
The oxygen-carrying protein in red blood cells. More haemoglobin means more oxygen delivered per litre of blood.
Learn more →Heat acclimation
Adaptations to repeated exercise in the heat, such as more plasma volume and earlier sweating.
Learn more →HIIT
High-intensity interval training: repeated hard efforts with recovery, such as 4 × 4 minutes.
Learn more →HRmax
Maximum heart rate. Falls by about one beat per year and barely changes with training.
Learn more →HRV
Heart-rate variability: variation in time between beats. Higher generally reflects better recovery; track the 7-day trend.
Learn more →Lactate threshold
The intensity above which lactate builds up in the blood faster than it is cleared — roughly the pace you could hold for about an hour.
Learn more →Live high, train low
Living at altitude to boost red cell mass while training near sea level to keep intensity.
Learn more →MET
Metabolic equivalent: 1 MET = 3.5 ml/kg/min, roughly resting oxygen use. Studies often express fitness in METs.
Learn more →Norwegian 4×4
Four 4-minute intervals at 90–95% of max heart rate with 3-minute active recoveries.
Learn more →Polarised training (80/20)
Doing most sessions easy and a few very hard, with little in between.
Learn more →Resting heart rate
Heart rate at complete rest, best measured during sleep. Drops as aerobic fitness rises.
Learn more →Running economy
Oxygen needed to run at a given speed. Better economy means a faster pace for the same effort.
Learn more →Trainability
How much an individual's VO2max responds to training — partly genetic, partly dose.
Learn more →VO2max
The maximum rate at which your body can take in, deliver and use oxygen during all-out exercise, in ml per kg of body weight per minute.
Learn more →VO2peak
The highest oxygen uptake reached in a given test. Used when a true plateau (VO2max) isn't confirmed, e.g. in patients or on a bike.
Learn more →Zone 2
Easy aerobic intensity below the first lactate or ventilatory threshold — you can hold a conversation.
Learn more →