ALPHA HAS NOTHING TO DO WITH MUSCLES.
BEING THE STRONGEST OR SMARTEST MAN IN THE WORLD HAS NOTHING TO DO WITH BEING ALPHA.
Spending your time in a gym does not make you alpha. There are numerous alphas who have never lifted a weight in their life. There are also many alphas who have never read a book. Alpha is more about attitude and natural disposition.
Thus, muscles and intellect may help a person become and remain an alpha; alpha is not some level that you reach and remain on forever without work.
It's like being in a pool. The alpha is the deep end, and to remain on this level, one must continue to tread water. If he stops working at improving his life and thus falls into the life of a beta or worse, he must either drown or return to the shallow end where he must be one of the children.
One final note regarding your example. After Marius turns 80 and all his muscles begin to transform into flab and diminish, does he too cease to be an alpha?
We must not define alpha by such things as muscles, wealth, or intellect.