Rainbow Dash burst into the basement of the library, ready for anything.
“Twilight!” she shouted. “Are you alright!?”
“Help!” Twilight wailed. “I’m being crushed!”
“Don’t worry, I’ll be right… oh come on.” Rainbow Dash just shook her head as she saw Twilight’s predicament. She lay on her back, seemingly trapped under a barbell. “Twilight-”
“It’s crushing me! I can’t breathe!” Twilight flailed all four limbs wildly as she shouted.
Rainbow Dash shook her head again, putting both her hooves to her face. “Twilight, that-”
“HELP!”
“Twilight, that barbell isn’t heavy enough to crush you! It only weighs ten pounds.”
“Huh?” Twilight stopped waving her legs.
“If that thing is keeping you from breathing, we need to get you to the doctor and get you a new ribcage.” She reached down, slid her hoof under the bar, and effortlessly lifted it off of Twilight.
“Oh.” Twilight smiled sheepishly.
“Not to mention the fact that you, you know, could just use your magic to move it. It would’ve been less effort than using your distress signal spell.”
Twilight sighed, and sat up. Her face was flushed, rather from embarrassment or effort, Rainbow Dash couldn’t tell.
“Sorry,” she said. “When I looked up information about weightlifting, I kept running into warnings about how you can injure yourself if you don’t lift properly, and I… I guess I overdid it a little.”
“Yeah, just a bit,” Rainbow Dash said. “Seriously, when you used that spell I thought you were being attacked by an Ursa Major or something. You know, just because getting in shape is a physical activity doesn’t mean you can just turn your brain off.” She gently rapped Twilight on the forehead. “Seriously. Weightlifting wasn’t a good place to start. You should start with something simpler.”
“S-simpler?” Twilight mumbled. “How can you get more simple than lifting a weight? If I can’t even get that right…”
“Hush.” Rainbow Dash silenced her with a hoof on her mouth. “Working out isn’t that tough to figure out. I mean, even I can do it.” She looked around the basement. She didn’t come down here often, but she was reasonably sure that it hadn’t been filled with exercise equipment. “What is all this stuff? Did you rent out the basement to a gym or something?
“No, nothing like that.” Twilight shook her head. “It’s just… I noticed that I’ve been putting on some weight lately, and I have to be in shape by the time the next gala rolls around.”
“Oh come on, you haven’t put on that much weight.” Dash gave her a poke in the stomach. She squished a little more than Dash expected. “And some ponies are just naturally a bit more pudgy than others. Nothing wrong with that.”
“But my family is not naturally pudgy! In fact, my mom is petite, my dad was a beanpole growing up, and Shining Armor had to work out for like four hours a day to build up respectable muscle mass!”
“Really?” Rainbow Dash cocked her head. “Because going by his haunches, you’d never know that-”
“Rainbow Dash!”
“Sorry.”
“And in case you’ve forgotten, I’m a princess. I’m supposed to try and be a role model for everypony to look up to, and that means that I have to do my best to keep myself in top physical shape!” She snorted and crossed her forelegs. “I can’t just let myself go. Especially not after they posted those pictures of me at Hayburger.”
“I don’t know about that,” Rainbow Dash said. “I mean, it’s pretty common knowledge that Celestia eats quite a bit of cake, and it’s not like it affects her reputation at all.”
“Yes, but she has a millennium of experience backing her up. I’m new at this!”
“And it’s not like you can’t tell either,” Rainbow Dash continued. “All that sugar seems to go straight to her rump”
“Dash, don’t talk about Celestia like that!”
“And let’s face it, if anything that’s boosted her popularity, if you know what I mean-”
“Dash!” She yanked on Rainbow’s tail with her magic.
“Oh, right. You realize that if you cut down on the hayburgers, nachos, and pancakes, you wouldn’t have this problem, right?”
Rainbow Dash cringed as Twilight gave her the stinkeye.
“Have you ever had Spike’s nachos? No way am I giving those up. I’ve been cutting back, but I’ll go insane if I can’t have some comfort food. Especially since Spike is always eating. It would be torture having to go on a diet with him being able to eat!”
“Why don’t you just have him go on a diet too?” Rainbow Dash asked. “You don’t want him to gain too much weight either.”
“Do you know how fast a dragon’s metabolism is? He could out-eat Pinkie Pie and he wouldn’t gain any weight.” Twilight sat on the floor like she was sulking. “I crunched the numbers. If I don’t do something I won’t even be able to fit into the gala dress that Rarity made for me.” She kicked at the barbell. “But I don’t know the first thing about trying to whip myself into shape!”
“Are you serious?” Rainbow Dash snorted. “You got fifth place in the Running of the Leaves even though you’d never done it before. You can totally figure it out!”
“That’s not the same! That was just jogging and making sure I paced myself. It’s not like I was exerting myself all that much.” She turned away. “Besides… I was probably in better shape back then anyway. I doubt I’d be able to even jog from here to Sugarcube Corner without having to stop and catch my breath.”
Rainbow Dash stared at her for a moment, then bonked her on the head.
“Ow! What was that for?”
“That was to get that brain of yours moving again, because apparently it isn’t working very well today. Seriously, your reason for not wanting to get exercise is that you’re too out of shape to do it? That’s the whole reason you need to get to it in the first place!”
“I know that,” Twilight said indignantly. “It’s just… it’s embarrassing. It’s something so basic, but even as a princess I can’t do it correctly? It’s pathetic.”
“All the more reason for you to work on it! Trust me, I know all about this sort of thing. You remember the Best Young Flier’s competition last year?”
Twilight nodded. “How could I forget?”
“Well, you remember how freaked out I was about trying to perform in front of the Wonderbolts and how I kept screwing up the Sonic Rainboom every time I tried to do it. You know why I had so much trouble? Because I was worrying too much about whether or not I could do it! When it comes to trying to get better at something, you need to just forget all that and quit worrying about how well you’ll do and just do it.”
“Easier said than done,” Twilight muttered.
“Well, I never said it was easy. It isn’t. It’s actually pretty hard. But that doesn’t matter. Maybe you won’t be able to run a mile or whatever right off the bat, but what’s worse, trying to run a mile and not being able to, or not even trying?”
“Trying and failing.”
Rainbow Dash put a hoof to her face. “No! That’s not what you were supposed to say. Okay, let me put this a different way. You want to get in shape because you want to be a good role model for everypony, right?”
Twilight nodded. “Well, that’s part of being a princess, yes. It’s one of my responsibilities as a ruler of Equestria.”
“Well, what do you think is going to inspire more ponies: being a perfect, unattainable ideal, or showing that even though you aren’t perfect you’re still trying to improve yourself?”
Twilight opened her mouth to answer, but bit her lip instead.
“Yeah, I thought so. Nopony’s perfect, not even me!” She winked.
“I guess it would be good for everypony to see that there’s nothing wrong with having to work to improve yourself. I mean, I put in plenty of time trying to improve my magic, even though I’m already good at it.”
“That’s the spirit!” Rainbow Dash patted her on the back. “Now, are you ready to go do some jogging?” Then she poked Twilight in the flank. “I mean, it’s up to you, obviously. I still say that you’d look fine even with a bit of pudge-”
“Rainbow!” Twilight shoved her away. “It’s hard enough even without you tempting me not to do it. Let’s just get going before I change my mind, okay?”
“What, you want me to come along?” Rainbow Dash gave Twilight a sideways glance. “But it’s my day off.”
“Rainbow, if I’m going to actually do all this, I need somepony to keep me motivated, and to make sure I don’t overdo it and hurt myself for real.”
“And make sure you don’t get trapped under your weights.”
Twilight chuckled. “Yes, and that. So are you going to help me or not?”
Rainbow Dash winked. “Of course I can. Now let’s get out of this basement. We’ll start with a brisk walk around Ponyville and we’ll work up from there. I’ll have an exercise program set up for you in no time.” She jumped up and flew to the top of the stairs. “So, you coming?”
Twilight took a deep breath and started up the stairs. “If you’re going to help me out, I wouldn’t miss it.”
Author's Note
A super-brief little snippet I threw together for a friend's birthday present.
Very rushed and unpolished, and still a day late. Go figure. 
Hopefully it's somewhat enjoyable nonetheless.
