By Patty Wilber
I might have a few parts that are a bit on the worn side.
The soccerized knees. The shoulders that have been yanked by horses on the lunge line or that have broken a fall or two. The stiffening back.
Geez! The creak of age!
As one gets older, muscles tend to change from the larger, bulker white fast-twitch muscle type II to red slow twitch fibers type I that are more suited to endurance.
In one study of pectoral muscle in women, after age 40, the the fast (type II) muscles decreased in size, but not number. After 60, there were significantly fewer type II fibers. Those fibers are associated with bursts of strength.
Total volume of type I muscle fibers did not change with age. However, those red fibers were fewer in number, but larger.
As one gets older, sometimes people stop moving various parts and those parts get stiffer and stiffer.