If you think the fitness revolution began with Jane Fonda, you don’t know Jack . . . LaLanne.

The legendary health crusader died Sunday at 96, three days after his last blog posting — and 60 years after his TV show first aired, on which he urged everyone to get off their couches, count their calories and take better care of their bodies.

His own bod was his best advertisement. A former weakling and sugarholic — a nutritionist’s lecture he heard at 15 changed his life — he pumped and jumped his way to perfection.

He never let up, not for years — marking his 70th birthday by towing 70 rowboats a mile and a half as he swam in heavy seas. In handcuffs! Even in his 90s, he was still working out in his home gym in California — when he wasn’t on the road, hawking juicers.

“My chest is 46 inches, my waist is 30 inches — and my wife is perfect!” he declared five years ago, when he and the mellifluously named Elaine LaLanne, 12 years his junior, visited The Post.

Gravity had whittled down his 5-foot-6 frame — in his blue jumpsuit, he looked like a Smurf — but he was mobbed in the lobby. Fans from as far afield as Texas and Trinidad rushed to greet the man who was as fast with a quip as he was with a barbell:

“Ten seconds on the lips, a lifetime on the hips,” he’d say, and “Put your muscle where your mouth is.”

Arnold Schwarzenegger, he boasted, called him “an ah-nimal.” Years before, they’d gone tricep-to-tricep at Santa Monica’s Muscle Beach, and LaLanne beat him at push-ups. To mark the occasion, the then-Governator gave him an embroidered jacket.

LaLanne was anti-Atkins, anti-steroids — and living proof you didn’t need Viagra to be frisky.

“Jack,” I said, after he barked out his commandments for good living — “Eat fruits and vegetables! Exercise every day!”–“Jack, you’re fantastic!”

“And we haven’t even slept together yet!” he replied. “Do ya snore?”

“Oh, Jack!” sighed Elaine.

Rest in peace, Jack. You deserve to.