I just want to say that exercise is an investment in life. People who don't exercise are sure to cause various diseases. People who exercise will be many times stronger physically and mentally than those who don't exercise. Proper exercise will only make you healthier, at least not live longer. It's hard to say. The fitness instructor you mentioned may have some sports injuries because of years of exercise. These are minor problems and will not affect your health. Don't worry too much. . .