Note: I've tried researching if paraplegics can do sit ups or not, but can't find a definitive answer. So unless I do, I'm going to have it that he can. After all, we are dealing with godlike beings here.
Sweat broke out on Loki's brow as he struggled to lift the weights Baldur had given him just one more time. Baldur sat in front of him on the floor, a proud smile lighting his handsome face. "That's it, Loki! You can do it. Just this one last time. For now." Baldur winked mischievously at Loki, who almost lost his concentration. His arm dipped for just a moment before he grunted and pushed onward, lifting the heavy weights above his head and lowering them slowly, always in control. That was one thing Baldur had instilled in him-your movements must always have control, even in times of fun, to avoid risk of injury.
And Baldur didn't just speak the words; he lived them. When Baldur touched your arm, you knew he had thought about it beforehand, so if he was gentle or if he was not, he had made the decision to be gentle or not and was aware of the consequences either way. While Frigga was teaching him magic, Baldur was helping him build the physical strength where he could, even without his legs, and both of them ensured that he kept up on his reading. Knowledge was power. A man who could think and adapt could outfight one who always did the same things over and over again.
And so each day was divided busily amongst study, exercise, and magic. Loki found that he enjoyed all of it, a lot more than he would have thought prior to the accident, when only training with weapons had mattered. Now he knew not just the basics of weapon use, but also the background of weapon making, having spent time at the forge with Baldur while the blacksmith created swords and knives. He had even been allowed to try his hand at the forge, with the guidance of the blacksmith, and the small knife he had created had become his when he was finished.
Baldur reached up and took the weights from Loki's hands, placing them on the table beside them as if they weighed no more than feathers. He stood and reached down for Loki, plucking him out of the chair just as easily. He walked to a nearby mat and placed Loki down on it, then sat at his feet with his hands on Loki's ankles. Loki groaned. Sit ups were utter torture, but the healers said that the spasms he experienced afterwards were a good sign, particularly the pain associated with those spasms. Loki let out a sigh and put his interlaced fingers behind his neck to support it in case he couldn't pull up using his abdominal muscles, then struggled into the first sit up. He lay back down, but not all the way; Baldur would not allow him to rest his upper body on the mat between sit-ups, only between sets. He counted off-one up down, two up down, three up down-finally making it to ten before allowing his shoulders to rest on the mat.
Baldur counted slowly with him to ten and then Loki started another set of ten. Each set became more of a struggle. By the time they reached ten sets and Baldur called a halt, Loki was utterly exhausted and drenched in sweat. Baldur lifted him back to his wheelchair.
"Come on. Let's take a walk to cool you down, then you can get cleaned up and we'll get lunch."
"Baldur?" Loki reached up and put a hand on Baldur's muscular forearm.
"Yes, Little Brother?"
Loki swallowed. He wanted to tell Baldur how much he loved him, but that would sound weak. "I...thank you. For all of your help."
Baldur ruffled Loki's hair. "You're welcome, Scamp. I can't have my favorite little brother languishing while the other is preparing to become a warrior, can I?"
Loki beamed. "Am I truly your favorite?"
Baldur leaned down close to Loki's face. "Don't tell Thor." He winked and then straightened, walking around behind the wheelchair to guide it through the halls as the first snows began to fall.