The 23-year-old was blighted by injuries at the start of his career at the Emirates Stadium.
However, the England international now feels that he is over the worst of his fitness woes.
"I'm 23 now and I am still growing. I am not afraid of getting hurt," he told the club's official website.
"A few years ago I had shoulder injuries, ankle problems and back problems and that was just me learning the other side of the game.
"Now I am just going into games and enjoying myself, not being scared of anything. The manager always tells me not to be afraid going into tackles. I am a totally different Theo Walcott now."
Walcott bagged his 11th goal of the season in Wednesday night's 3-0 win at Wolverhampton Wanderers.