Lukaku became the Merseyside club's record signing when he made a permanent move to Goodison Park from Chelsea after a successful loan spell last season.
The 21-year-old has scored four goals in 10 Premier League matches in the current campaign, but has not been at his best for Martinez's side.
And the Spaniard feels that Belgium international Lukaku was feeling the effects of coming into the season on the back of playing in the World Cup in Brazil.
Martinez is in no doubt that his big-money recruit is starting to show what he is capable of and knows there is more to come from the powerful frontman.
He said: "I think we're seeing it every game [that he is improving]. Since [we played] Villa after the [last] international break we've been able to work more on individual and more specific aspects from a physical point of view.
"We're starting to see real signs of freshness and someone who is ready to kick on. The hangover from the World Cup is over, we're starting to see the power and penetration that Romelu has and it’s pleasing."
Lukaku will be aiming to add to his goal tally when Everton face Sunderland at the Stadium of Light on Sunday.
