I carried my 3 year old daughter (she's about 34 pounds) into the grocery store from the car and wasn't even winded!
I used to sweat and be completely out of breath and eventually I just stopped carrying her and held her hand. But, she likes to be carried, and I WANT to oblige that desire while she's still little!!!
I absolutely couldn't believe that once I put her in the cart, I still felt completely relaxed and normal!