The first time Sakura heard of exercise, she was utterly confounded. Who would want to cause themselves pain just to be the best, fastest, strongest? Sure, she was vain, as was everyone else, but to push yourself that hard for just the pleasure of winning-- only to lose again later? She didn't understand. But it was a way of life, and she had always been told to do so, so Sakura tried her hardest to please her parents until she could get done with the nonsense.
By the time Ino came along, Sakura had just about had it with exercise. She was teased in school, she had a big forehead, her parents wouldn't understand… and was working out helping any of this? Nope. In fact, it was taking away from the time she could study. So she, in her own way, could get better. And stay better. Because learning didn't cause any pain—sure, headaches sometimes, but those went away quickly. But when Ino came along… Sakura learned about bloodlines, and the fact she didn't have one. This meant to keep up with Ino she had to exert herself physically. And so Sakura kept on trying, this time for Ino.
Sasuke came along next. Now Sakura had learned that training kept you thin, so it wasn't like she had a choice or anything. She had loved Sasuke forever… and the crush wasn't going away. So she could be like Hinata, and admire from the background, or be brave and try to tackle Sasuke for herself. Ino was helping too, in her own way, so Sakura kept working at the hateful exercise. To be strong for a little bit Ino, but most of all Sasuke.
Naruto was like no one she had ever met. He didn't have any reason whatsoever for trying—he had no friends, no family, no crush except her, and guys didn't do that sort of thing. Plus he never did really want her—she knew that right away. That was the core reason why she kept pushing him down—he needed to work on his own dreams. Become Hokage. Beat Sasuke. She was an in-between, but helped as much as she could. Nevertheless, Naruto's work ethic had scared her at first. He had no reason for trying whatsoever, not like Sasuke. Not that she had any reason to stay fit. Until a little time passed, and then she knew —for her team, she had to be strong.
Lee was scariest of all. She could do not anything but try to understand, but she failed. Someday, she thought. If I keep on working, I might understand someday. And so Sakura worked next for Lee.
Tsunade burst into her desperate life like a roll of thunder. Like nothing she had ever experienced, Tsunade pushed, and pushed, and pushed. Pushed so hard that the only thing Sakura could do was to burst into admiration, because hatred was an emotion she never hoped to experience. Exercise was the killer then. She loathed it. Hated hated hated. But Sakura tried to never hate anything, and Tsunade, her model, basked in exertion. And if her model was going to bask in it, what was to say she couldn't?
When Sakura was fifteen, exercising was her life. She worked out with the rest of them, tried to surpass all others, tried to earn the title of champion that she could never keep. Did all the pointless things she never had understood—so that maybe, just a little bit, she could do it without trying. And she did it. Exercising was still hard for her—but it wasn't worth struggling over anymore. She grew into it, did it to stay healthy, keep up with everyone. So she wouldn't die on a mission. But she did it for herself.
Many, many years later, Sakura looked back on her life. She looked back on all her successes, her struggles, and tried to understand. She looked at her memories of her parents, Ino, Sasuke, Naruto, Lee, Tsunade and all the others she had ever known. She looked back at her fears, her confusions, her annoyances, and couldn't solve anything. All her book learning, useless. Except for exercise.
For Sakura understood now. The act of running through the trees, bounding up and slamming a fist into someone's face—it wasn't to be the best that people did these things. It wasn't for themselves. Nobody chose to be a ninja for themselves. Someone always put them up to it, made them try harder, made them push themselves. And it was that someone that was important. The fierce joy she had for flying—jumping off tree trunks of her own power and for use of whatever she could think of —that wasn't for her. She loved it. She adored it. But it was for others. For all the someones in her life that kept pushing her, loved her enough to show her beyond her boundaries.
Because beyond the boundaries, those ridiculous, suicidal boundaries, lay peace.