The defender told BBC Radio Nottingham: "You've either got the aggression streak or you haven't and if you haven't there's no point forcing it.
"When I give them (the strikers) a kick in training it perks them up a little bit and they give me a bit back, and that makes a difference on a Saturday."
Foster believes the physical side to football is more prominent in the Blue Square Premier.
He said: "Sometimes you've got to be tough and aggressive because there are some big strong strikers in this league.
"You've got to make sure you dominate them and make sure you stamp your authority on the game.
"It's a big part of the game in this league."
Source: BBC Sport
Source: BBC Sport