I’ve been looking a little deeper into a landmark study that compared exercise volume, aging, and body composition. The study showed that in older subjects who maintained a high exercise volume and consumed enough food, their resting metabolic rate did not decline. This is quite extraordinary, but I was also struck by other parts of the study.
The study looked at sedentary and active men in two age groups, young and older. What was noticeable to me is that young, sedentary men had a significantly higher metabolic rate than older, active men. The difference added up to about 182 more calories per day being burned by the younger group at rest.
To me, this says that the older active individuals start each day "in the hole", so to speak, by 182 calories. And even given their high level of activity, they still only averaged 17% body fat in the study, the same amount as the young, sedentary group.
The key difference in the two groups was the amount of fat-free mass, as the younger men had almost 9 pounds more. Fat-free mass is the primary determinant of resting metabolic rate, so this made the difference for these two groups.
All this points to the importance of retaining fat-free mass during the aging process. Otherwise, a person has to keep doing more and more activity just to keep body fat from increasing. Resistance training is the only method that can truly stop the age-related decline in fat-free mass, and the associated age-related decline in resting metabolism.