“Sleep is key to regulating brain function,” says Nick Hounslow, celebrity trainer and instructor at Cycle House in West Hollywood, California. “It repairs your body and enables everything from strength to stamina.” Hounslow, who frequently wakes up at 4:30 a.m. to teach a spin class, suggests going to bed a little hungry; hitting the sack on a full stomach can slow down your metabolism and negatively interfere with sleep cycles. Not sure if you’re getting the most out of z-time? Try Sleep Cycle ($0.99), an app that tracks sleep patterns throughout the night and gently wakes you while you’re in the light stage of sleep. By outsmarting your cycle you can avoid that groggy feeling.