Estimate your fitness age from VO2 max.
VO2 max — the peak rate at which you can take up and use oxygen — falls at a fairly predictable rate through adult life, roughly a third of a point per year in men and a little less in women. Inverting that trend line answers the question the other way round: at what age would your measured VO2 max be typical? That age is your fitness age, and the gap against your real age is the number worth tracking over training blocks.
Expected VO2 max
Expected VO2 max = intercept - decline x age, with intercept 56 and decline 0.33 for men, 48 and 0.28 for women
Fitness age
Fitness age = (intercept - measured VO2 max) / decline
Educational estimate only. Not medical advice — discuss results with a qualified clinician before changing treatment, medication or exercise.
A graded treadmill or cycle test in a lab is the reference standard. Field estimates from a Cooper twelve-minute run, a Rockport walk test or a running watch are close enough for tracking trends.
Untrained adults commonly add three to six VO2 max points over eight to twelve weeks of consistent aerobic training, which moves fitness age by roughly ten to eighteen years on this trend line. Gains slow sharply after that.