He's the storm everyone avoids. She's the sunshine no one can ignore. When a power outage shoves yoga instructor Delilah Hart into Wilder Gym, she collides with Lennox Wilder—the grump who rules the weight floor like it's a war zone. Her studio is on the line; his hard-won order is non-negotiable. From stolen corners and dueling playlists to a very public "noise complaint," their turf war turns into a truce neither of them trusts. Forced to co-train, Delilah's calm meets Lennox's control, and sparks snap in every rep, stretch, and almost-touch. Clients start rooting for them. The gym starts feeling like home. And the man who never smiles keeps finding excuses to stay in her orbit. But winning the space isn't the same as winning each other. Delilah won't risk her future on a man who lives behind iron walls. Lennox won't let anyone see the soft place he swore off years ago. When a career-making opportunity arrives—with strings that tangle business and desire—both have to decide what they're willing to bend for…and what's worth breaking the rules. Grumpy/sunshine banter, gym-crush heat, and slow-burn tension—TRAINING THE GRUMP delivers a forced-proximity romance where discipline meets desire and the only thing heavier than the weights are the feelings.