Total muscle mass is thought of as one of the intrinsic limiting factors of aerobic power. But it is not yet clarified how the total muscle mass limits the magnitude of aerobic power. The purpose of this study was to clarify the relationship between total muscle mass and aerobic power and to make a further discussion conscerning its limiting factors. 17 sedentary students with a mean age of 19.3 (18-23) years, and 17 varsity footballers 19.9 (19-21) years old, were measured for lean body mass, which was an approximate indicator of the total muscle mass, by underwater-weighing method and VO₂ max by bicycle ergometer. The correlationship between lean body mass and VO₂max for sedentary students was found to be higher (r=0.821) than for footballers (r=0.595) . It was also shown that footballers had a significantly larger VO₂max per 1kg of lean body mass than sedentary students. Previous studies showed that the increment of VO₂max through endurance training was caused by the increment of such factors as mitochondria, maximum cardiac output and maximum stroke volume, and was not by lean body mass. So, it was concluded that lean body mass was a reasonable limiting factor for sedentary students, but was not a stable factor of VO₂max because of lower linearlity for footballers and the significant difference on VO₂max per 1kg of lean body mass between two groups.