Hey that looks like it's going back up! To be critical on this - also curious what source that comes from, testosterone level checks are not common on healthy routine blood tests and I wonder if they were at one point and aren't now. Also pair that alongside obesity rates.
Fat tissue consumes testosterone, excess adipose makes _free_ testosterone appear lower on tests, full stop. It doesn't mean anything necessarily. It also is completely independent of muscle mass. Also what suppresses testosterone hormone production the most, is stress (and related conditions).
That graph could be an opposite coloration predicate equally valid.
strong men create productivity
productivity create abundance
abundance create weak men
weak men create money supply
money supply create low testosterone
low testosterone create hard times
hard times create strong men
weak men create hard m2