Work the Upper Back
“I’m not too sure about this Rainbow Dash.” Fluttershy worried, voicing her concern to her friend. “A-are you sure this will be alright?”
“Of course I am Fluttershy.” Rainbow nodded, confident in her plan. “Trust me, this is the best workout I've even had and I know you’ll love it.”
“A-all right.” Fluttershy replied, walking out of the mare’s changing room. “I-I’ll follow you.”
Rainbow Dash was well known to be a mare in shape, despite sporting a massive K cup bust. Joining the Wonderbolts only seemed to strengthen her body; but she still needed to maintain this physique. Upon recommendation from her teammates, she joined the Cloudsdale Gym. But there was something peculiar about this gym. Every time Rainbow seemed to go, she would be completely exhausted the following day, but not the typical type of exhaustion she normally had when working out. Curious, her closest friend, Fluttershy asked her about it, and the next thing she knew, Rainbow dragged her to her next workout session. Needless to say, the mare was incredibly shy about this; especially since she’d be forced to show off her colossal O cup bust.
Walking out of the changing room, Fluttershy, wearing an embarrassing tight white tank top, with an even tighter pair of light green shorts looked to Rainbow Dash; who was in an equally revealing matching set of black sports bra and flank hugging shorts. This attire was enough to make the mare want to hide away somewhere, but she knew her friend wouldn’t allow it. She agreed to this, and she would see it through to the end. Beckoning with her finger, Rainbow started walking in a direction; to which Fluttershy followed. Walking along the way, both mares watched a number of other pegasi work out. Some lifted heavy weights with arms, backs, legs, and even wings. While other seemed to focus on cardio, such as running, jogging, and even flying in place.
“Here we are.” Rainbow calmly announced, pointing towards a door. Looking at the door, Fluttershy saw it held both a storm cloud with lightning bolt, as well as a barbell weight. “These two are the best personal trainers they have here. It’s perfect!”
“A-are they nice?” Fluttershy asked, cowering a little behind her friend. “I-I don’t want them to yell at me.”
“You’ll be fine Fluttershy.” Rainbow sighed a little, turning to pat her friend on the head. “Just do as I do, and you’ll be fine.”
Opening the door, Fluttershy’s eyes widened at what she saw. In the room, both working single handed barbells were two stallions; both of who she knew from Ponyville, Buck Biceps and Thunderlane. But what was the most shocking, was what was dangling between their loose gym shorts. Both stallions had massive cocks. Bigger than anything Fluttershy thought a stallion could have. Suffice to say, she had the strongest blush at the sight of such bestial dicks. Rainbow didn’t seem as nervous, quite the opposite, she was expecting it. Both stallions quickly realized that they weren’t alone and turned to look at the pair.
“Oh Rainbow, back again?” Bulk asked, then his eyes met with Fluttershy’s. “Oh and Fluttershy is here too?!”
“Yep, she’s here for the same thing I got last time.” Rainbow announced, starting to lift her top, letting her large breasts bounce free.
“Wha-waah?!” Fluttershy almost shouted in surprise and confusion. “R-rainbow, what are you-”
“It part of the exercise.” Rainbow explained, grabbing at Fluttershy’s top. “Having a massive rack is killer on the back, so these guys came up with an exercise to help strengthen our back.”
“B-but...this is...” Fluttershy replied, nervous as she was being forcibly stripped in front of the two stallions.
“I understand you’re nervous.” Thunderlane commented, though the moment he got up, he dropped his shorts, showing how much girth his cock had. “But you don’t have to worry, we are professionals. Right Bulk?”
“What was that?” Bulk replied, still sitting but with Rainbow’s chest already sandwiching his cock in a titfuck motion. Fluttershy was gasping and panting in confusion while Thunderlane only face palmed. "What? We both know the routine works."
"R-routine?" Fluttershy stuttered, looking back and forth between the stallions.
"He's not wrong." Thunderlane replied, trying to compose himself. "You see, despite how perverted this must seem, it does help your back muscles. As you can see, Rainbow's using her back muscles in order to utilize her breasts. Bulk's penis is simply something she can press against and use to keep in a steady motion." After explaining, he could tell Fluttershy was believing him, or at least was not as nervous about it. "Rainbow told us you often have back aches, well this could help strengthen your back so you won't have aches. Interested?"
Fluttershy thought about it, she thought about it for a good long while, all while Rainbow continued to slide her large breasts up and down. Bulk tensed up, making sure to hold back any orgasm he was going to have, and with Rainbow as his partner, it would be quite the challenge. The mare, despite telling herself this was just a mutual workout, her competitive nature would often drive her to press her breasts all around the large cock, trying to sandwich it hard between her soft chest mounds. Thunderlane couldn't help but watch, it wasn't like Rainbow minded. If anything, she liked it when he watched. If Fluttershy wasn't there with them, she'd adjust herself and let both of them titfuck her at once. So long as it worked her back, that's all that mattered. But Rainbow wasn't some easy whore. Her pleasurable titfuck was the farthest she'd let them go. She never even put her face near their cocks. Though they caught her taking in their strong, musky scents before.
"Okay, I've thought it over." Fluttershy finally said, drawing Thunderlane's attention back to her. With a little hesitation, she lifted her top upwards, letting her colossal bust bounce free. "I'd like to give it a try."