Poor sleep has ongoing effects on fitness levels, primarily by impairing recovery and influencing hormone regulation. Inadequate sleep can lead to increased levels of cortisol, a stress hormone that can promote weight gain and reduce muscle recovery. Sleep deprivation also disrupts the balance of ghrelin and leptin, hormones regulating hunger and satiety, which can lead to poor dietary choices. Furthermore, lack of sleep affects cognitive function, reducing focus and motivation for exercise. Overall, quality sleep is essential for optimal performance, muscle growth, and maintaining a healthy lifestyle.