Don't go beyond failure for maintenance muscle groups. And do not do any technique that are exceedingly hard on the nervous system either.
To me 'hard enough' is lifting for strength always trying to beat a record.
Pick 1 main compound movement for non-spec muscles and train it for 4-6 sets of low rep (I like the 5/4/3/2/1 or 3/2/1/3/2/1 or 5/4/3/5/4/3 for this purpose).
You CAN a secondary exercise for muscles such as back and chest, but make it an isolation movement.