The Latics face Norwich today.
"The hardest thing for any team in this league is to score goals," said Martinez. "They have prolific scorers.
"Norwich have been really impressive. They have grown into the league and shown great belief. They have a freedom and bravery and willingness to create chances.
"It doesn't surprise me how well they have done.
"The old feelings of inferiority from teams who got promoted, that need to keep clean sheets and trying to win games by being defensive, has gone."