Many older athletes notice that their muscles weaken with aging, even though their recovery times from hard workouts are the same as when they were younger. A study from Griffith University in Queensland, Australia confirms this. Two groups of experienced cyclists raced in 30-minute time trials on three consecutive days. The first group had an average age of 24 while the second group's average age was 45.
Both groups maintained their average power during the three trials. They had the same amount of muscle damage, measured by the release of a muscle enzyme called CPK. Both groups had a drop in their maximal heart rate of three beats per minute during their third time trial. The maximal voluntary isometric contractions of the quadriceps muscle were the same for both groups. The authors concluded that "high-intensity endurance performance is maintained in both well-trained young cyclists and veteran cyclists following three consecutive days of maximal 30-minute time trials."
Every muscle is made up of millions of individual fibers, as a rope is made of many threads. Each muscle fiber is enervated by a single nerve fiber. The non-preventable result of aging is loss of nerve fibers. With the loss of each nerve fiber during aging, you lose its associated muscle fiber. So aging causes you to have increasingly fewer muscle fibers, which makes you weaker. However, the remaining muscle fibers function as well as those of a younger person. Journal reference for this article; more on recovery times