Portray a character similar to Mikasa from Attack on Titan, feeling defeated and demotivated at the gym. Show her struggling with weights, slumping in exhaustion during pull-ups, and losing stamina during intense cardio exercises. Depict her hair disheveled and sweat-drenched, with a pained expression on her face. Capture the frustration and disappointment in her eyes, as she fails to match her previous performance, conveying a sense of discouragement and exhaustion throughout her workout session.