well thats how rhyming slang tends to work, e.g. you would hear someone say "there was a barney" meaning there was a fight (that's Barney Rubble = trouble); or to "have a butcher's" meaning to have a look at something (Butcher's hook = look). Using the first part of the word or phrase is part of what makes it an in-group marker; those who know will understand, hence calling someone a seppo is just combining the cockney rhyming slang the ANZACs came across during the war with an Australian stylism. i would normally take that as friendly banter rather than derogatory.

it literally says “Fuck the Democratic Party“ did you even read it

Just chiming in to reinforce Carmelians point that the sarcopoenia in particular is a highly likely aetiological predisposing factor for OP's described experience (as noted, for a male >50yoa it's pretty much a given), and strength/resistance training is the only realistic compensating strategy. You're correct that they don't achieve the same, and that both are required, and that something is better than nothing. But its also true that the strength component seems to be more overlooked in the popular approaches to the vicissitudes of aging, so bears particular emphasis