Liv Gold, MS

It should be easy: A person works a full day, drops into a vigorous boot camp after work, and then falls into bed exhausted, but satisfied. She’s asleep in minutes, right? That would be nice, but for many people, high-intensity evening classes actually delay the onset of sleep. Researchers think this is because workouts ramp up heart rate so much that the body has trouble recovering before bedtime (Oda & Shirakawa 2014).