“The body-brain loop works both ways. Just as physical conditioning shores up the brain’s performance, the reverse can also be true: a mental drain can impact muscular endurance. One study of Italian soccer players showed that doing fatiguing brain teasers before going to the practice field made them commit more errors in controlling and passing the ball. Another study of twenty-one young boxers showed that too much time on phones playing video games affected their speed reactions in the ring.”