These are the following TV Characters I picked that I thought to be very fit (healthy).
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Gina (Nurses)
Liz Williams (Night Court)
Billie Young (Night Court)
Rachael Crawford (Family Matters)
Eddie Winslow (Family Matters)
Mary Richards (Mary Tyler Moore)
Tiffany Maloy (Unhappily Ever After)
A.C. Slater (Saved By The Bell)
June Cleaver (Leave It To Beaver)
Peter Burns (Melrose Place)
Michael Kuzack (L.A. Law)
Zelda Spellman (Sabrina, The Teenage Witch)
Chrissy Snow (Three's Company)
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It seems that these characters never gained an ounce of weight. I know Rachael Crawford was a healthy eater and good exerciser because that one episode where she was helping Carl lose weight and she was eating a carrot and on her way to the gym to exercise. Gina, Liz and Billie were TOO thin IMO. You could see a lot of episodes where Eddie Winslow was lifting weights or working out. Then there was that one episode where Jack Tripper's brother visits him and they are eating at that restaurant. The waiter brings by cake and Chrissy says: "oh, none for me thanks, my waist line." A.C. Slater was always lifting weights or wrestling on Saved By The Bell.

Ranger Walker of "Walker, Texas Ranger" because.... he's Chuck Norris.

How about The Big Ragu from Laverne and Shirley? He always looked like he was auditioning for an exercise show. :)

Mary Richards (TMTMS) used to exercise regularly, as did Tony Banta (Taxi).

Van Montgomery on Reba. He must have been fit since he was a football player!

Chachi Arcola on Happy Days.
The Fonz on Happy Days, he was shown lifting weights.
Sonny Lumet on Bosom Buddies-They showed her working out.

Robbie Douglas on My Three Sons
Elly May Clampett and Jethro Bodine on The Beverly Hillbillies
Carol Post on Mister Ed

Stanley Wojciehowicz from Barney Miller.

All of the lifeguards on Baywatch.

Hutch (David Soul) from Starsky and Hutch was considered a "health nut" who exercised a lot, watched what he ate, drank protein shakes, went on fasts. By the last season of the show the actor had put on about 15 pounds due to a back injury he suffered and had to wear a back brace, and the character's "healthy" habits weren't really mentioned anymore - iirc.

Starsky (Paul Michael Glaser) was the "junk food junkie" on the show but the actor was into health food and had a buff body, most especially in the 3rd season of the series.

Barney Stinson-How I Met Your Mother.

He was seen shirtless in a few episodes and is very fit. NPH works out.

Tony Randall-Felix Unger
Clint Eastwood-Rowdy Yates
Marlo Thomas-That Girl
Alan Alda-Hawkeye
Leah Remini-Carrie from King of Queens
Patricia Heaton-the MIddle, ELR

Wally Cleaver - Leave it to Beaver
Dick Van Dyke - The Dick Van Dyke Show
Wayne Rogers - M*A*S*H
Freddie "Boom Boom" Washington - Welcome Back Kotter
Charles - Charles In Charge
Gilligan - Gilligan's Island
John Boy Walton - The Waltons
Maxwell Smart - Get Smart