Round 6: Jasmine
Round 7: Cinderella
Round 8: Tiana
Round 9: Snow
Round 10: Anna
Round 11: Belle
Round 12: Elsa
Round 13: Aurora

Definitely. Everyone else does much more physically demanding activities and more constantly.

By far. The others does more than her.

Just saying, Rapunzel pulls Mother Gothel all the way up into the tower every day using her hair as a pulley.

It's not that she isn't a physically fit girl, but I just find Merida to be "a copy" of all of the princesses who preceded her in prowess, strength, and agility. She's my least favorite, kind of, because she is so much of a duplicate next to everyone else.

It's mostly her hair that does the work and I highly doubt Punz has any muscle definition

It's a close call between Rapunzel and Ariel. (I changed my vote three times already)

In the end, I just feel Rapunzel does more : she does housework, she does ballet, she climbs, she stretches, she pulls Gothel up the tower everyday without fail, she struggles against Gothel's chains, etc.

Ariel moves a rock out of the way to her grotto, swims with Eric to the shore... what else? I can't remember anything.

^Ariel kicks waterlogged debris in front of a shark ( it looked like a whole desk to me), and physically attacks Ursula at the beginning of the climatic battle. Ariel actually has the physical strength to force Ursula's neck back 180 degrees by simply pulling on Ursula's hair. This basically causes Ursula to misfire on Flotsam and Jetsam.

Out of these, I think Ariel is the least physically fit one, since:

Punzie does acrobatic things with help of her hair,
Pocahontas runs like a deer,
Mulan went to war instead of her father,
And Merida was climbing up mountains and riding a horse.

Merida is definitely at least second when it comes to fitness. Rock climbing without a harness, shooting a bow while riding on a horse, and she even shows skill with a sword. Ariel does nothing that compares to that.

Compared to the others remaining, she is the least physically fit.