On an autumnal Wednesday in Inverness, Cynthia Harland and Ginny Felch were chatting after their thrice weekly pickleball game at the First Valley tennis court, as Ms. Harland’s puppy scampered in the sun. 

The two were discussing how lighthearted and low-stress pickleball can be. “If I don’t laugh 10 times before I get in my car, I . . .