Jessica Simpson is feeling the burn!
The singer, 29, complained that she overdid it after a Wednesday workout with personal trainer Mike Alexander.
"Why am I still hurting from our workout earlier?" she Twittered to him. "I'm getting old! See you tomorrow with a pouty face and sore buns."
He Twittered back that she's "a badass" whose "efforts know no limitations. And I can deal with looking at that pouty mug..."
Simpson Twittered back, "I will never understand why people attack for a laugh."