Brain retraining

On the exercise front, I’m increasing my “load,” that is, the total weekly kilometers, slowly and surely, seeking for once to avoid a knee or calf or tendon or foot injury. But on the writing front, today I just jumped back in and put in seven hours of labor. Should I have eased back into it? I can’t afford any delays, so no, the answer is no. I did find myself yawning, a trifle headachy, midway through the day, but I stuck with it. I guess I’m retraining the brain through bludgeoning it.