Staying up late has a great influence on fitness. First of all, staying up late will lead to physical fatigue, affect the recovery and growth of the body, and then affect the fitness effect. Secondly, staying up late will affect the body's metabolic rate, making it easier for the body to store fat and gain weight. In addition, staying up late will also affect the human immune system and increase the risk of infection. Therefore, in order to maintain a good fitness effect, it is best to avoid staying up late.