The struggling Saints conceded three times in the first half as Bournemouth ran riot in front of their home fans, and not even a Taylor Harwood-Bellis goal early in the second was enough to light a fire under them.
"They make 20 fouls to our 10 or whatever it is - I think that sums up the whole game," Martin told Sky Sports.
"We were soft. The problem - forget style of play - is if you don't want to run and fight properly, make contact, take things personally, like a duel we didn't come out of the ball at all in the first half, then it's going to be a problem."
The Saints remain 19th in the table with one point from their opening six games, and on Monday they only managed brief spells in which they looked like a cohesive Premier League team.
"I thought I made enough of a deal about Bournemouth and the way they approached the game and how good they are at certain things, but obviously it wasn't enough, because we looked like we were unprepared for that, which, considering the work we've done is crazy," Martin explained.
"I will never, ever come out of here and blame the group of players, we are together. I didn't like a lot of what I saw, and I was hurt by the lack of spirit and fight.
"I told them that, that's nothing I haven't said in the dressing room but it's always on the leader and that's my problem to sort out," he added.
