Exercise activates signaling between hypothalamus region of your brain and your pituitary and adrenal glands. But what happens when the only time you have available to work out is late at night? A study published in The Journal of Sports Medicine and Physical Fitness analyzed the effects using 20 male medical students.

According to sleep diaries kept by subjects, and saliva samples taken the morning after a 90 minute late night football match, there was no impact on sleep quality or cortisol response, but the 9:30 PM timing of exercise did alter hypothalamic-pituitary-adrenal signaling the following day.