原文： First of all, it's important to understand that exercise is key to maintaining overall health. Regular physical activity not only improves physical fitness, but also helps reduce the risk of chronic diseases, such as heart disease and diabetes.

重新描述： Understanding the importance of exercise for maintaining good health cannot be overstated. Engaging in regular physical activity offers benefits beyond just improving physical fitness, as it can also reduce the likelihood of developing chronic illnesses like heart disease and diabetes.