The 31-year-old has been in impressive form this season, scoring the winner against Dundee on Saturday after helping his side to a 3-3 Champions League draw with Manchester City days earlier.
"I think it all starts going into training. The training has been great, as have the physios and coaches," Brown is quoted as saying by Sky Sports News.
"It wasn't always like that last year. It didn't always put a smile on your face when going into training. It was difficult, it was slow, the training itself wasn't hard enough.
"This season, all the lads are enjoying it, they want to work hard. It doesn't matter if it's Monday, Tuesday, Wednesday, Thursday or Friday; training has been exceptional."
Celtic top the Scottish Premiership table with 19 points, four above second-placed Aberdeen.