Michael Phelps, Katie Ledecky, Missy Franklin and Ryan Lochte are all in action at the Arena Pro Series at Mesa on Friday and Saturday, live on NBC Sports Live Extra.
The Big Four of U.S. swimming are competing together in a Pro Series meet for likely the last time before the U.S. Olympic Trials in Omaha, Neb., from June 26-July 3.
Phelps returns to Mesa for the third straight year. It was a comeback meet in 2014, following a 20-month competitive retirement, and 2015, following a six-month suspension.