Sources in Las Vegas tell us Lamar's been working out like crazy for the last month at a private fitness center called The R Club -- it's the gym in the gated community where he's now living. We're told he's putting in about 3 hours a day with a personal trainer.
He's starting early too -- 7 AM for an outdoor run ... plus yoga, basketball, and weightlifting.
The ex-NBA baller had thickened up over the past 18 months or so -- since the split from Khloe.
Based on the pic ... his workout regimen is working. We don't wanna call post breakup hotness, but seems perfectly timed with him and Khloe finally going through with the divorce.