During maximal performance the absolute VO2 max was the same in obese and nonobese subjects but for a given body weight, lean body mass, and leg muscle (plus) bone volume, VO2max was reduced by 23.8, 16.3, and 24.5% respectively, in the former group. It was concluded that obesity though having minimal affect on responses to submaximal exercise is nevertheless associated with a marked reduction in physiological performance at or near maximal effort.
This research was carried out at The Brompton Hospital in London in the paediatric department of Professor Simon Godfrey. It showed that the the aerobic performance measured as maximum oxygen uptake was surprisingly the same for obese and non-obese girls when expressed as an absolute value (litres/min). Thus they appeared to be just as fit as their non-obese age-matched peers.
However when the aerobic performance was expressed as the maximum oxygen uptake per kilogram of body weight that had to be moved when running or walking then the obese subjects show a reduced performance of nearly 25% because of the extra weight of fat that they had to move.
Journal of Applied Physiology. 1975 Mar;38(3):373-6