Nice theory.
A friend I knew in graduate school told me that four hours of serious concentration equaled ten hours of hard physical labor. I don't know if it's true, but since I've worked sixteen and eighteen hour days at challenging physical jobs like being a dresser in the theater--imagine running up and down flights of stairs, helping actors rip off costumes and hustle into the next outfit, all with time frames limited to seconds before you dash across to do the same thing with someone else. My definition of a difficult job is high stress and poor pay interspersed with phases of boredom.
Anyway. That was a lengthy interjection. Suffice to say that I've worked jobs that ended with me trembling at day's end with physical and emotional exhaustion.
My muscles may not ache at the end of a day of writing, but I do feel just as wrung out. Also exhilarated . . . or depressed . . . or uncertain. In the last 48 hours, I've drafted, revised and submitted an article to a bimonthly magazine that regularly publishes my stories, fine-tooth-combed a quarter of my memoir so I can submit the final draft in as perfect a condition as possible, and jotted original draft for some new scenes in one of my novels, and had a preliminary meeting with an editing client. Not to mention the life stuff of caring for horses in below freezing weather, helping my youngest sister with her fifteen month and month old daughters, gone to shamanism class and so on.
I am not complaining--I love my life and am grateful for the writing opportunities continuously opening for me. I'm just saying that, though my waist isn't as trim as when I raced up and down all those steps and back and forth through the backstage area, I'm not lolling around on the sofa with a box of candy, either.