The hardest part is starting. You talk yourself into changing into your workout clothes. You talk yourself into sitting down at the dining room chair. Once those first steps are accomplished, you remind yourself of your goals: make it a mile then maybe two. Rewrite Chapter 3, then depending on how long that takes, rewrite Chapter 4, which was once Chapter 10. You'll run for 45 minutes. You'll write for an hour. The goals might be different, but the process, how it all works together, is all the same.
But it's still hard. You stretch out your leg muscles. You crack your knuckles and then start typing, just trying to get your mind ready for what's ahead.
Then, you go. Your feet pound the pavement, and your fingers hit against the keyboard. You hit your stride. You feel like you can keep going and going and going, and no one will ever stop you. You can run for miles. You can finish one chapter, then two, then three.
Then there's those other times, when the going gets difficult. Your breathing gets labored, your leg muscles tighten. The words don't flow out and your fingers stop chattering against the keyboard.
But you push yourself, tell yourself that you just need to keep going, that you can do this. That you might not look your best while you're running past all the homes in your neighborhood, that you might not be putting your best words down... but you're making progress and you just need to turn off your internal critic/editor off for just a few more minutes. You're working toward your ultimate goal: losing weight and getting healthy, as well as finishing this novel. It takes patience and it takes practice, but you will get there.
Then, you finish for the day. Your run turns to a jog, which turns into a walk. A few more thoughts trickle out onto the page. You think about tomorrow, about how you'll improve, about what route you'll take next, and you feel wonderful for everything you've just accomplished.