As per your question i would like to answer in parts. So First part is about diet, Diet plays a major role in transformation, some say diet is 70% and exercise is 30%, some people say 90-10, big guys eat big to get big, more carbs and proteins, but athletes dont use weights that much and have a restricted diet, secondly workout so athletes like Usain, run marathons, and in that process they lose muscles that's why they are skinny, bodybuilders prefer HIIT workouts, and short time exercises like 20 min running, cycling etc, but athletes can do this all day long
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