04/23/2014 07:13 EDT | Updated 06/23/2014 05:59 EDT

Smiling, relaxed Michael Phelps happy to end retirement and race again

MESA, Ariz. - Michael Phelps is making a comeback after nearly two years out of competitive swimming for the simplest of reasons: he missed it.

The 22-time Olympic medallist says he's been having fun and smiling a lot during training in his hometown of Baltimore. Having shed the weight he piled on since retiring after the 2012 London Olympics, Phelps will resume his career starting Thursday at a meet in Arizona. He'll swim the 100-meter butterfly, having dropped his plans to compete in the 100 freestyle the same day.

Phelps was noncommittal about whether his comeback would lead to swimming in the 2016 Rio Olympics. However, he admits that if he wants to compete at the highest level, he has to be ready by this summer.