Originally Posted by
roccobike
As to which of the above is the biggest factor, sadly it's the human motor. In that regard, age is, sadly, a big factor.
Age may not have to be that big of a factor, after all.
A
review of masters athletes studies found that most of their VO2max declines were due to reduced training volume, not aging, and that the athletes who maintained training volume lost very little.
Burtscher, J., Strasser, B., Burtscher, M., & Millet, G. P. (2022). The Impact of Training on the Loss of Cardiorespiratory Fitness in Aging Masters Endurance Athletes. International journal of environmental research and public health, 19(17), 11050. https://doi.org/10.3390/ijerph191711050