You know those days at the gym when you’re bench-pressing six plates or you’re one-arming your body weight in preacher curls, and one rep you’re pumped and stoked, split-setting cable rows with wide-grip pull-downs, you’re knocking out reps and sets fast as you can rack the plates—but then, the next set, you’re toast. Wasted. Every curl or press is just more effort. Instead of powering through, you’re counting, sweating. Panting.