"I had months of being on some pretty heavy painkillers, so it has been great to get my back fixed," he told the Courier-Mail.
McCullum is looking to bring a similar attitude and style of cricket to the Heat as what was played under his reign as New Zealand skipper.
"I want to grab hold of fans with the attractive and entertaining brand of cricket we are going to play this season," McCullum said.
"If anyone is in any doubt, I want people to know what they are going to get from the Heat.
"The beauty about being captain is I can give the guys the freedom to go out there and chance their arms.
"Sometimes cricket can be strangled by fear (of failure) and that is the last thing I want.
"I want to promote the Heat players to go out there and play a free and fearless game and have some fun.
"We want to win but the main thing is we want to provide an entertaining product."