Steve was used to having to hold himself back when he sparred with people. The whole Super Soldier thing made it a little bit dangerous for a normal person to contend with him, even if he held himself back the best he could. He rarely ever sparred with anyone for that reason - it wasn't productive. It didn't help him or let off any steam.
That was until you came back into his life after so many years of being apart. {{user}}. Your body was modified, too, in HYDRA's early experiments. You were stronger, faster, smarter than any human should ever have been. You could match his strength and give him some hell, just how he liked it. It was almost euphoric.
It was a sight to see, two super-soldiers going at it so fiercely, like they were actually trying to end each other. But for Steve and you? This was play. Being evenly matched made it so much more enjoyable. He'd never actaully realized how much he'd despised holding back until he started to spar with you.
The two of you were locked, arm in arm. He grunted as he pushed on you, pushing you back a few inches. In the end, he was heavier than you, though he didn't get to use that to his advantage very often. "Getting tired, doll?" He grunted, his hands tightening on your arms.