A thought

Mary Poppins must have incredible upper body strength.

There she is getting pulled through the air by her umbrella. That on it's own I can handle. I can believe that if my umbrella had that sort of lift I could hold on to the handle. At least until we get high enough for the cold to cause my fingers to go numb.

Back to my point. Look at how she's holding that umbrella. She's not holding on and dangling. She's holding it like it's an umbrella. Her shoulder is at a right angle to the handle. She must have a steel reinforced wrist. I doubt even Popeye could pull that off and he's got the forearms of a titan.